[written February 25, 2007]
I have posted a three-minute "Tour of Giant Gap" movie on YouTube, see
http://www.youtube.com/profile?user=rufus16180339887
where it is currently the latest offering. By way of a sound track, I read an 1876 newspaper article about a visit to Lovers Leap.
Sunday, February 25, 2007
Friday, February 16, 2007
Intractable Obstacles
[written February 16, 2007]
What a day, what a wonderful day!
For weeks now, I have been saying, to myself, and to whomever, "I should take my chainsaw down the Green Valley Trail, and cut up some of the trees which fell this winter, and blocked it."
The weather has been nothing but perfect, well, most all of January was sunny, then followed some storms, some rain, and now, sun upon sun, a northeast wind, birds singing and chattering as though Spring is really here, and finally, and at long last, the weeks spent hunched in front of my computer, doing geometry, dividing the determinant of one square matrix by the determinant of another, oh glory of all glories, seemed far far too much. It was time to bust a move. Time to escape.
So I carefully cleaned the air filter on my chainsaw's carburetor, washing it in warm and soapy water, set it to dry, built a peanut butter sandwich upon some kind of blueberry-cinnamon bread, grabbed my ancient frame pack from the back outside wall of the little hexagonal cabin, threw in gloves, fully fueled chainsaw, ear protectors, hat, water, and sandwich, and, picking up some loppers at the last moment, I set off down the old old trail.
I had an ulterior motive. I wished to reach the High Ditch, which runs from the very east end of Green Valley to the very west end, with some fuel left in my saw, and work west along the ditch. This will make a fine trail, someday. About 80% has already been cleared. Some really hard work remains. So that was The Plan: conserve fuel, ignore this and that leaning manzanita, focus upon the various trees, and, having taken care of that most pressing business, proceed, in keeping with my own peculiar and cherished agenda: the High Ditch Trail.
The best-laid plans of mice oft gang a'gley, or whatever, and so also with my plans. For as I descended the ancient path, once the busy avenue for a thousand iron-shod mules (see how the bedrock bosses, rising from the bed of the trail, are rounded? human feet never wore them down, in that way), as I descended, I found manzanita which could not be idly passed, I found other trees, which I had forgotten, in my aged and forgetful way, and so, off came the pack, out came the saw, on went the gloves and ear protectors, and work was essayed.
Finally I reached the Big One, a two-foot-diameter Digger Pine fallen directly along the trail, only a few switchbacks below the Echo Tree.
The Echo Tree is an Incense Cedar, which, by its size, one would surmise could be but fifty years old. Except, it grows in plant-stunting serpentine, and is likely more than one hundred and fifty years old. It is scarcely fifty feet high, and a little over two feet in diameter, but I know from conversations with Bernie and Harriet Denton, that the Echo Tree was thriving in the 1930s, when they used to spend their summers in Green Valley. Those skinny little kids would swim the North Fork all summer long.
They called it the Echo Tree because a good shout to the west will echo back nicely, from the far wall of Ginseng Ravine. They considered it to mark exactly half the way to the North Fork. It provides welcome shade.
Bernie and Harriet would never walk the Green Valley Trail without each carrying a long thin stick, poking ahead to awake the rattlesnakes.
At any rate, passing the Echo Tree, I soon reached the Worst Offender, the aforementioned Digger Pine.
It did not look good. My saw has a sixteen-inch bar, the tree was on the beefy side of two feet through, and lay along fifty or so lineal feet of trail. Thus many cuts were called for, severing it into rounds, each round to be rolled away into the manzanita, below.
I tried one cut, at an advantageous spot, and was rewarded by being able to open ten feet of trail, rolling a massive log but a short distance.
That took care of the small end of the tree. Looking at the rest, I realized I would run my saw right out of fuel, and still not be done, making the other ten cuts needed.
I thought to myself, "This is just the job for Ron Gould's big chainsaw," and with that pleasant and rational thought, I packed up my gear and headed down and down and down.
Unfortunately, in only a little ways I came to one of the many charming Corridors of Manzanita which frame the old trail. This Corridor evoked the idea of an historic Gold Rush trail; one could almost see the bearded, red-shirted miners trudging along, hemmed in by the gnarled red branches.
And this Corridor had shrunk to dimensions even a deer might disdain. I could not even traverse the thing, with my chainsaw projecting from the top of my pack. There was really no choice. I had to work, and work hard.
So I cut and cut and cut, and pitched brush and pitched and pitched, and rested, and then cut and cut and cut and pitched and pitched and pitched.
I realized I was only a few yards above the Secret Side Trail to the Secret Old Miner's Cave in the Serpentine Fanglomerate of Ginseng Ravine.
Thus, I was only a few yards above yet another tree, this one a Douglas Fir, which fell ten years back, and is a real nuisance. There was no longer any chance of working the High Ditch. Too much fuel had been expended in the Corridor. So I waltzed down to the Secret Side Trail and attacked the Douglas Fir.
It was only sixteen inches or so in diameter, only a smidgin too large too cut through in one pass, and I made one cut, and then most of second, which pinched shut on me before I could finish, so I made a third cut between the two, which would have left me with two four-foot lengths to roll out of the way. Well within my capabilities.
An inch or so before the third cut was completed, my saw ran out of fuel.
What followed would have provided some good entertainment, had anyone been there to see.
I went in search of levers, confident I could just break the remaining wood in the second cut, and snapped one hefty, yet too-rotten, branch after another. Did I quit? Oh no! I just kept on scouting around for bigger and better levers. I found some. Using pieces of broken levers, I could lift the one free end an inch at a time, and shove the broken lever pieces underneath. I gradually, gradually, moved the free end full sixteen inches, to the accompaniment of various cracking sounds from the second-cut-which-had-pinched-shut-on-me. But it never broke.
Many a time I lay full flat on the ground, grabbing whatever was handy, and used all the power in my legs to try to move the eight-foot log that one last inch which would break the pinched cut.
To no avail.
I found natural wedges and used boulders to pound them into the pinched cut, which had opened considerably, the pinched cut which needed so very little to break that last vestige of solid wood.
To no avail.
Again and again I lay on the ground and strained with my legs. Again and again I pounded the ad hoc wedges deeper. Again and again I levered the free end up, or to the side, shimming it and chocking it in various ways, and using small boulders, with near-incredible cleverness, as fulcrums. Or fulcri.
To no avail.
I knew that, once in a blue moon, when the saw ran out of gas, I could start it up again for a few seconds. So I tried that.
To no avail.
At last, sweaty, dirty, and even leafy, with ants climbing all over me and through my hair, I had to give up. I left my wedges and levers just as they were. God. An hour, at least, I spent. I came within an inch of cutting through the damn log with my saw, and it ran out of gas. Did I give up? Yes.
But not without a fight.
Still, I lost. I lost that one. Darn it!
So, I trudged back up to my pack, finished pitching manzanita off the Corridor, loaded everything, and made a nice slow step-after-step ascent of the trail.
It was a day of bright sun and blue sky, of bright snow in the distance, of the fewest and scantiest of clouds, of a brisk northeast wind aloft, but the more typical upslope winds at the surface. I had a chance, of course, to ponder geology, for I really cannot stop pondering geology (it may well be a vice), and I concluded that the east wall of Moonshine Ravine, over towards Casa Loma, was really too high and too steep to be a result of mere stream incision, that it represented, in fact, a distinct record of the glacier which broke out of Canyon Creek into the North Fork canyon, either 65,000 years ago, or 130,000 years ago, or both; so that the gap, or pass, in the dividing ridge, should better be called Glacier Gap, than Hogback, which latter is its historic name, not that anyone remembers that that is so.
No, around here, the guiding concept of local history is, "I moved here in 1955, and you moved here in 1975; end of story."
Such was a wonderful if strenuous day in the great canyon of the North Fork of the American River.
What a day, what a wonderful day!
For weeks now, I have been saying, to myself, and to whomever, "I should take my chainsaw down the Green Valley Trail, and cut up some of the trees which fell this winter, and blocked it."
The weather has been nothing but perfect, well, most all of January was sunny, then followed some storms, some rain, and now, sun upon sun, a northeast wind, birds singing and chattering as though Spring is really here, and finally, and at long last, the weeks spent hunched in front of my computer, doing geometry, dividing the determinant of one square matrix by the determinant of another, oh glory of all glories, seemed far far too much. It was time to bust a move. Time to escape.
So I carefully cleaned the air filter on my chainsaw's carburetor, washing it in warm and soapy water, set it to dry, built a peanut butter sandwich upon some kind of blueberry-cinnamon bread, grabbed my ancient frame pack from the back outside wall of the little hexagonal cabin, threw in gloves, fully fueled chainsaw, ear protectors, hat, water, and sandwich, and, picking up some loppers at the last moment, I set off down the old old trail.
I had an ulterior motive. I wished to reach the High Ditch, which runs from the very east end of Green Valley to the very west end, with some fuel left in my saw, and work west along the ditch. This will make a fine trail, someday. About 80% has already been cleared. Some really hard work remains. So that was The Plan: conserve fuel, ignore this and that leaning manzanita, focus upon the various trees, and, having taken care of that most pressing business, proceed, in keeping with my own peculiar and cherished agenda: the High Ditch Trail.
The best-laid plans of mice oft gang a'gley, or whatever, and so also with my plans. For as I descended the ancient path, once the busy avenue for a thousand iron-shod mules (see how the bedrock bosses, rising from the bed of the trail, are rounded? human feet never wore them down, in that way), as I descended, I found manzanita which could not be idly passed, I found other trees, which I had forgotten, in my aged and forgetful way, and so, off came the pack, out came the saw, on went the gloves and ear protectors, and work was essayed.
Finally I reached the Big One, a two-foot-diameter Digger Pine fallen directly along the trail, only a few switchbacks below the Echo Tree.
The Echo Tree is an Incense Cedar, which, by its size, one would surmise could be but fifty years old. Except, it grows in plant-stunting serpentine, and is likely more than one hundred and fifty years old. It is scarcely fifty feet high, and a little over two feet in diameter, but I know from conversations with Bernie and Harriet Denton, that the Echo Tree was thriving in the 1930s, when they used to spend their summers in Green Valley. Those skinny little kids would swim the North Fork all summer long.
They called it the Echo Tree because a good shout to the west will echo back nicely, from the far wall of Ginseng Ravine. They considered it to mark exactly half the way to the North Fork. It provides welcome shade.
Bernie and Harriet would never walk the Green Valley Trail without each carrying a long thin stick, poking ahead to awake the rattlesnakes.
At any rate, passing the Echo Tree, I soon reached the Worst Offender, the aforementioned Digger Pine.
It did not look good. My saw has a sixteen-inch bar, the tree was on the beefy side of two feet through, and lay along fifty or so lineal feet of trail. Thus many cuts were called for, severing it into rounds, each round to be rolled away into the manzanita, below.
I tried one cut, at an advantageous spot, and was rewarded by being able to open ten feet of trail, rolling a massive log but a short distance.
That took care of the small end of the tree. Looking at the rest, I realized I would run my saw right out of fuel, and still not be done, making the other ten cuts needed.
I thought to myself, "This is just the job for Ron Gould's big chainsaw," and with that pleasant and rational thought, I packed up my gear and headed down and down and down.
Unfortunately, in only a little ways I came to one of the many charming Corridors of Manzanita which frame the old trail. This Corridor evoked the idea of an historic Gold Rush trail; one could almost see the bearded, red-shirted miners trudging along, hemmed in by the gnarled red branches.
And this Corridor had shrunk to dimensions even a deer might disdain. I could not even traverse the thing, with my chainsaw projecting from the top of my pack. There was really no choice. I had to work, and work hard.
So I cut and cut and cut, and pitched brush and pitched and pitched, and rested, and then cut and cut and cut and pitched and pitched and pitched.
I realized I was only a few yards above the Secret Side Trail to the Secret Old Miner's Cave in the Serpentine Fanglomerate of Ginseng Ravine.
Thus, I was only a few yards above yet another tree, this one a Douglas Fir, which fell ten years back, and is a real nuisance. There was no longer any chance of working the High Ditch. Too much fuel had been expended in the Corridor. So I waltzed down to the Secret Side Trail and attacked the Douglas Fir.
It was only sixteen inches or so in diameter, only a smidgin too large too cut through in one pass, and I made one cut, and then most of second, which pinched shut on me before I could finish, so I made a third cut between the two, which would have left me with two four-foot lengths to roll out of the way. Well within my capabilities.
An inch or so before the third cut was completed, my saw ran out of fuel.
What followed would have provided some good entertainment, had anyone been there to see.
I went in search of levers, confident I could just break the remaining wood in the second cut, and snapped one hefty, yet too-rotten, branch after another. Did I quit? Oh no! I just kept on scouting around for bigger and better levers. I found some. Using pieces of broken levers, I could lift the one free end an inch at a time, and shove the broken lever pieces underneath. I gradually, gradually, moved the free end full sixteen inches, to the accompaniment of various cracking sounds from the second-cut-which-had-pinched-shut-on-me. But it never broke.
Many a time I lay full flat on the ground, grabbing whatever was handy, and used all the power in my legs to try to move the eight-foot log that one last inch which would break the pinched cut.
To no avail.
I found natural wedges and used boulders to pound them into the pinched cut, which had opened considerably, the pinched cut which needed so very little to break that last vestige of solid wood.
To no avail.
Again and again I lay on the ground and strained with my legs. Again and again I pounded the ad hoc wedges deeper. Again and again I levered the free end up, or to the side, shimming it and chocking it in various ways, and using small boulders, with near-incredible cleverness, as fulcrums. Or fulcri.
To no avail.
I knew that, once in a blue moon, when the saw ran out of gas, I could start it up again for a few seconds. So I tried that.
To no avail.
At last, sweaty, dirty, and even leafy, with ants climbing all over me and through my hair, I had to give up. I left my wedges and levers just as they were. God. An hour, at least, I spent. I came within an inch of cutting through the damn log with my saw, and it ran out of gas. Did I give up? Yes.
But not without a fight.
Still, I lost. I lost that one. Darn it!
So, I trudged back up to my pack, finished pitching manzanita off the Corridor, loaded everything, and made a nice slow step-after-step ascent of the trail.
It was a day of bright sun and blue sky, of bright snow in the distance, of the fewest and scantiest of clouds, of a brisk northeast wind aloft, but the more typical upslope winds at the surface. I had a chance, of course, to ponder geology, for I really cannot stop pondering geology (it may well be a vice), and I concluded that the east wall of Moonshine Ravine, over towards Casa Loma, was really too high and too steep to be a result of mere stream incision, that it represented, in fact, a distinct record of the glacier which broke out of Canyon Creek into the North Fork canyon, either 65,000 years ago, or 130,000 years ago, or both; so that the gap, or pass, in the dividing ridge, should better be called Glacier Gap, than Hogback, which latter is its historic name, not that anyone remembers that that is so.
No, around here, the guiding concept of local history is, "I moved here in 1955, and you moved here in 1975; end of story."
Such was a wonderful if strenuous day in the great canyon of the North Fork of the American River.
Monday, January 15, 2007
Green Valley News
[written January 15, 2007]
This morning I received a call from Steve Hunter of Colfax, an active man with a penetrating and curious mind, who has explored these Placer County canyons as have few if any others, since his childhood in the early 1950s.
I mean, as dimly as I am aware of his exploits, I know they exceed my own. Roping down the middle of thundering waterfalls: for goodness' sake, you wouldn't catch me doing that.
But Steve Hunter has. And not just once, either. He's seen gorges you only can see if you actually *do* rope down waterfalls.
Steve loves Green Valley. Yesterday he and Dan Mathers and several friends dropped down into the great canyon on the good old Green Valley Trail, hewed to the western side of things, and eventually found themselves just across from the Gold Ring Mine, on the sand bar at the head of the pretty pool on the river which reflects Lovers Leap, looming half a mile high to the west.
Here they busied themselves collecting the garbage left there last summer by some miners, and without wasting much in the way of time, they hauled several loads up to the old Incense Cedar tree in the meadow, near the wooden trough.
What, were they calling it quits?
Oh no.
From there they worked east to the Old Hotel Site, below Joe Steiner's Grave, where another mess of garbage lay in frozen masses. This too they gathered unto themselves, but this they carried up and up and up and up and up, and finally, completely out of the canyon.
Steve reports that they had to leave a frozen sleeping bag, weighted with ice, behind, but they certainly made some great strides in keeping the fine old Valley clean.
We made sounds about plans to plan to go back down and haul up the rest of the trash, with as many people as we can muster, and hit a lick on the trail too, and who knows but these fantasies may become real.
This morning I received a call from Steve Hunter of Colfax, an active man with a penetrating and curious mind, who has explored these Placer County canyons as have few if any others, since his childhood in the early 1950s.
I mean, as dimly as I am aware of his exploits, I know they exceed my own. Roping down the middle of thundering waterfalls: for goodness' sake, you wouldn't catch me doing that.
But Steve Hunter has. And not just once, either. He's seen gorges you only can see if you actually *do* rope down waterfalls.
Steve loves Green Valley. Yesterday he and Dan Mathers and several friends dropped down into the great canyon on the good old Green Valley Trail, hewed to the western side of things, and eventually found themselves just across from the Gold Ring Mine, on the sand bar at the head of the pretty pool on the river which reflects Lovers Leap, looming half a mile high to the west.
Here they busied themselves collecting the garbage left there last summer by some miners, and without wasting much in the way of time, they hauled several loads up to the old Incense Cedar tree in the meadow, near the wooden trough.
What, were they calling it quits?
Oh no.
From there they worked east to the Old Hotel Site, below Joe Steiner's Grave, where another mess of garbage lay in frozen masses. This too they gathered unto themselves, but this they carried up and up and up and up and up, and finally, completely out of the canyon.
Steve reports that they had to leave a frozen sleeping bag, weighted with ice, behind, but they certainly made some great strides in keeping the fine old Valley clean.
We made sounds about plans to plan to go back down and haul up the rest of the trash, with as many people as we can muster, and hit a lick on the trail too, and who knows but these fantasies may become real.
Friday, January 5, 2007
The Mysterious Ming Sun Tai
[written January 5, 2007]
***Curiosities Bearing Upon the History of Gold Run***
"At twilight, in the placer-scarred bed of Canyon Creek, South of Dutch Flat, Ming Sun Tai lighted a stick of incense from the glowing end of his fifty-cent cigar."
Over many years of enquiry into the history of Dutch Flat, Gold Run, etc., a number of curiosities have crossed my path. For instance, James Stewart of Gold Run, who once owned the "800 acres now for sale," comprising most of the Diggings, and the lower two miles of Canyon Creek, was not only born here, around 1885, but was a student of the local history, and amassed a large collection of materials, much of which was lost after his death, when his house was looted. Rumor had declared his fine old house full of gold nuggets.
This was around 1965 or so. Another Gold Run resident, hearing of this, walked out to the old Stewart place, in the Diggings, to see the looting for herself, and picked up a number of papers scattered in the mud.
Thirty years later, she let me see these papers. Among them was a letter written by Stewart, and dated to 1931, which described the discovery of gold at the head of Indiana Ravine, in 1851, and mentioned that the rich ground there was drift-mined, until, eventually, a Chinese company headed by one Tia Sing leased the old workings and hydrauliced away what remained.
Hence the Secret World, that isolated pit on the verge of the North Fork canyon, with its little stone cabin.
Now, one should not blindly trust historical sources, not even James Stewart, who grew up in this area. He was born too late to see hydraulic mining in full swing, although he did see it; in fact, there are photographs extant showing the young James Stewart, neatly dressed, watching a monitor at work, around 1895.
And the annual Report of the State Mineralogist, for 1896, records a Chinese company working at Indiana Hill. This can only be the very same company Stewart mentions, in his letter of 1931.
However, in 1896, this Chinese company could not have legally hydrauliced the old drift ground of the Secret World. Either we must imagine they operated illegally, or we must conclude that Stewart was mistaken. To me it seems much the more likely Stewart was mistaken, and that the Secret World was hydrauliced before the end of 1881, when the injunction against further discharge of mine tailings at Gold Run took effect.
That is, whatever the Chinese Company was up to in 1896, it was not hydraulic mining.
I wish I had known James Stewart. He seems quite an interesting man. He was the personal friend of Franklin Delano Roosevelt and of author Jack London, for instance. Could he have been acquainted, also, with author Hugh Wiley? The man who created the character of James Lee Wong, Chinese detective extraordinaire, Yale-educated James Lee Wong, a chemist?
Oh yes, James Stewart might have known Hugh Wiley; Hugh Wiley may well have stayed with the Stewarts at Gold Run, just as Jack London did.
At any rate, somehow, some way, Hugh Wiley came to know this area.
In 1921 Hugh Wiley wrote a short story titled "Joss." I will give a little excerpt, which the miracle of the Internet brought my way only this morning:
*******
At twilight, in the placer-scarred bed of Canyon Creek, South of Dutch Flat, Ming Sun Tai lighted a stick of incense from the glowing end of his fifty-cent cigar. The incense burned dull red at the origin of the twisted thread of smoke which spun in the early moonlight that lay on the Western slope of Moody Ridge. He set the stick of incense on a grey boulder and fixed it upright with three little pebbles.
"Pai seung tai," the Chinaman whispered. "In the love of a man's ancestors, he accomplishes the worship of the gods." He continued his course up the bed of Canyon Creek. A thousand feet farther on he lighted another stick of incense. To his left lay a half mile of open flat, slashed and bruised and welted from the conflict which had waged in the days when yellow gold lay from the grass roots to bedrock beneath.
*******
For more, see
http://books.google.com/books?q=%22Hugh+Wiley%22+%2B+Joss&btnG=Search+Books&as_brr=0
That Wiley used the phrase "gold from the grass roots to bedrock" shows that he really knew something about this area; for, there was no cap of "young volcanics" hiding the Eocene-age auriferous gravels, as was so common to the south around Foresthill. It was gold-bearing at the surface, and all the way down to the bedrock, hundreds of feet below.
So. For all these years I never even suspected that an author named Hugh Wiley existed.
Follow the link, and read Wiley's "Joss." It's not the highest of all faluting, but it's worth a read. The difference between a diamond and a sapphire can mean everything.
***Curiosities Bearing Upon the History of Gold Run***
"At twilight, in the placer-scarred bed of Canyon Creek, South of Dutch Flat, Ming Sun Tai lighted a stick of incense from the glowing end of his fifty-cent cigar."
Over many years of enquiry into the history of Dutch Flat, Gold Run, etc., a number of curiosities have crossed my path. For instance, James Stewart of Gold Run, who once owned the "800 acres now for sale," comprising most of the Diggings, and the lower two miles of Canyon Creek, was not only born here, around 1885, but was a student of the local history, and amassed a large collection of materials, much of which was lost after his death, when his house was looted. Rumor had declared his fine old house full of gold nuggets.
This was around 1965 or so. Another Gold Run resident, hearing of this, walked out to the old Stewart place, in the Diggings, to see the looting for herself, and picked up a number of papers scattered in the mud.
Thirty years later, she let me see these papers. Among them was a letter written by Stewart, and dated to 1931, which described the discovery of gold at the head of Indiana Ravine, in 1851, and mentioned that the rich ground there was drift-mined, until, eventually, a Chinese company headed by one Tia Sing leased the old workings and hydrauliced away what remained.
Hence the Secret World, that isolated pit on the verge of the North Fork canyon, with its little stone cabin.
Now, one should not blindly trust historical sources, not even James Stewart, who grew up in this area. He was born too late to see hydraulic mining in full swing, although he did see it; in fact, there are photographs extant showing the young James Stewart, neatly dressed, watching a monitor at work, around 1895.
And the annual Report of the State Mineralogist, for 1896, records a Chinese company working at Indiana Hill. This can only be the very same company Stewart mentions, in his letter of 1931.
However, in 1896, this Chinese company could not have legally hydrauliced the old drift ground of the Secret World. Either we must imagine they operated illegally, or we must conclude that Stewart was mistaken. To me it seems much the more likely Stewart was mistaken, and that the Secret World was hydrauliced before the end of 1881, when the injunction against further discharge of mine tailings at Gold Run took effect.
That is, whatever the Chinese Company was up to in 1896, it was not hydraulic mining.
I wish I had known James Stewart. He seems quite an interesting man. He was the personal friend of Franklin Delano Roosevelt and of author Jack London, for instance. Could he have been acquainted, also, with author Hugh Wiley? The man who created the character of James Lee Wong, Chinese detective extraordinaire, Yale-educated James Lee Wong, a chemist?
Oh yes, James Stewart might have known Hugh Wiley; Hugh Wiley may well have stayed with the Stewarts at Gold Run, just as Jack London did.
At any rate, somehow, some way, Hugh Wiley came to know this area.
In 1921 Hugh Wiley wrote a short story titled "Joss." I will give a little excerpt, which the miracle of the Internet brought my way only this morning:
*******
At twilight, in the placer-scarred bed of Canyon Creek, South of Dutch Flat, Ming Sun Tai lighted a stick of incense from the glowing end of his fifty-cent cigar. The incense burned dull red at the origin of the twisted thread of smoke which spun in the early moonlight that lay on the Western slope of Moody Ridge. He set the stick of incense on a grey boulder and fixed it upright with three little pebbles.
"Pai seung tai," the Chinaman whispered. "In the love of a man's ancestors, he accomplishes the worship of the gods." He continued his course up the bed of Canyon Creek. A thousand feet farther on he lighted another stick of incense. To his left lay a half mile of open flat, slashed and bruised and welted from the conflict which had waged in the days when yellow gold lay from the grass roots to bedrock beneath.
*******
For more, see
http://books.google.com/books?q=%22Hugh+Wiley%22+%2B+Joss&btnG=Search+Books&as_brr=0
That Wiley used the phrase "gold from the grass roots to bedrock" shows that he really knew something about this area; for, there was no cap of "young volcanics" hiding the Eocene-age auriferous gravels, as was so common to the south around Foresthill. It was gold-bearing at the surface, and all the way down to the bedrock, hundreds of feet below.
So. For all these years I never even suspected that an author named Hugh Wiley existed.
Follow the link, and read Wiley's "Joss." It's not the highest of all faluting, but it's worth a read. The difference between a diamond and a sapphire can mean everything.
Tuesday, January 2, 2007
Miscellany
[written January 2, 2007]
Happy new year, 2007 should be a good one!
The other day I approached my teenage son with an excellent idea: "I will first put the chainsaw in my old backpack; next, I'll put that old backpack on your broad shoulders; then, away we will go, down and down and down, into the depths of Green Valley, there to clear brush from the High Ditch."
To which he replied in a series of rather emphatic and mostly monosyllabic negatives, scarcely comprehensible, exclaimed in his curious teenage slang.
I decided not to press the issue, just then. Perhaps a negative would ripen into a maybe. A day later I recalled that the Green Valley Trail itself is getting so badly overhung by manzanita, that this business of carrying chainsaws in backpacks is maybe not an idea worthy of the brightest star in the heavens. So I rephrased my Plan: now he would carry the chainsaw a short distance, very short, really, and I would cut the gnarled deep red branches, and he would toss them off the trail.
Another series of foreign-sounding exclamations, all negative. Sigh.
So this morning I put the damn saw in the damn pack, and carried it down to the uppermost bad section all by myself. I worked over a reach of about two hundred yards and achieved something, less than I had imagined, better than nothing. The day was grey and cool and good for trail work.
Ron Gould suggests that we should round up a real work party and hit the whole trail. A good idea. The manzanita is getting worse and worse in a number of different trail reaches. Supposing we were to carry some of the dratted garbage up and out, from the end of the West Trail, down by the river, well, a frame backpack is the best tool for garbage, and the manzanita would drag and catch and claw at our packs and turn an already tiresome task into a bitter fight. So a bit of manzanita trimming is definitely in order. There are, also, one or two new trees down on the trail, which need cutting into pieces before they can be moved.
Life is more than trails and saws.
Music, music, music. Antonio Carlos Jobim! I rec'd a CD for Christmas, titled "Elis & Tom," the amazing Elis Regina singing the songs of the amazing Tom Jobim. One song especially excited my interest, Águas de Março, or Waters of March; here Jobim joins Elis in a duet. I Googled around in search of more information, for it seemed such an exceptional performance, and found a video of the actual recording session, in Los Angeles, in 1974!
What? How could that be?
It was on YouTube, of which I had heard but not seen. I naturally avoid such sites because I have such a poor internet connection, it takes forever to download content. For the Waters of March, however, forever was fine. I waited, I waited, I waited, and at last I watched.
Really really great!
So. I saw that anyone in the world can upload videos to YouTube. I quickly assembled a few short pieces of geometrical animations I had made years ago. See
http://www.youtube.com/profile?user=rufus16180339887
The above page also contains a link to the Águas de Março video, which I highly recommend, especially if you like Brazilian music.
Happy new year, 2007 should be a good one!
The other day I approached my teenage son with an excellent idea: "I will first put the chainsaw in my old backpack; next, I'll put that old backpack on your broad shoulders; then, away we will go, down and down and down, into the depths of Green Valley, there to clear brush from the High Ditch."
To which he replied in a series of rather emphatic and mostly monosyllabic negatives, scarcely comprehensible, exclaimed in his curious teenage slang.
I decided not to press the issue, just then. Perhaps a negative would ripen into a maybe. A day later I recalled that the Green Valley Trail itself is getting so badly overhung by manzanita, that this business of carrying chainsaws in backpacks is maybe not an idea worthy of the brightest star in the heavens. So I rephrased my Plan: now he would carry the chainsaw a short distance, very short, really, and I would cut the gnarled deep red branches, and he would toss them off the trail.
Another series of foreign-sounding exclamations, all negative. Sigh.
So this morning I put the damn saw in the damn pack, and carried it down to the uppermost bad section all by myself. I worked over a reach of about two hundred yards and achieved something, less than I had imagined, better than nothing. The day was grey and cool and good for trail work.
Ron Gould suggests that we should round up a real work party and hit the whole trail. A good idea. The manzanita is getting worse and worse in a number of different trail reaches. Supposing we were to carry some of the dratted garbage up and out, from the end of the West Trail, down by the river, well, a frame backpack is the best tool for garbage, and the manzanita would drag and catch and claw at our packs and turn an already tiresome task into a bitter fight. So a bit of manzanita trimming is definitely in order. There are, also, one or two new trees down on the trail, which need cutting into pieces before they can be moved.
Life is more than trails and saws.
Music, music, music. Antonio Carlos Jobim! I rec'd a CD for Christmas, titled "Elis & Tom," the amazing Elis Regina singing the songs of the amazing Tom Jobim. One song especially excited my interest, Águas de Março, or Waters of March; here Jobim joins Elis in a duet. I Googled around in search of more information, for it seemed such an exceptional performance, and found a video of the actual recording session, in Los Angeles, in 1974!
What? How could that be?
It was on YouTube, of which I had heard but not seen. I naturally avoid such sites because I have such a poor internet connection, it takes forever to download content. For the Waters of March, however, forever was fine. I waited, I waited, I waited, and at last I watched.
Really really great!
So. I saw that anyone in the world can upload videos to YouTube. I quickly assembled a few short pieces of geometrical animations I had made years ago. See
http://www.youtube.com/profile?user=rufus16180339887
The above page also contains a link to the Águas de Março video, which I highly recommend, especially if you like Brazilian music.
Wednesday, December 6, 2006
The Rarest Erratics
[written December 6, 2006]
The rarest glacial erratics are to the west, away from the high country, away from any obvious evidence of glaciation. They are old; but how old?
From about 5,500 feet in elevation and up, one sees abundant signs of the most recent, "Tioga" glaciation, which ended a scant 12,000 years ago. But the Tioga is only one of many. It is thought that, over the past 800,000 years, glacial climates have dominated, with warm "interglacial" climatic episodes (like today's climate) comprising as little as 10% of the total. And it has long been understood that the most recent glaciation of magnitude, the Tioga, was preceded by earlier, more intense glaciations.
By 1975 I was much on the alert for signs of these older glaciations. Such signs are not too easy to find, here on the west slope of the Sierra, where very abundant rainfall and snowfall tend to blur moraines into formless glacial till, and eventually, strip away that till altogether.
When glaciation takes place, there is a "firn line," usually imagined to be a contour line of fixed elevation. Above this elevation, snow accumulates into glacial ice; below this elevation, it may snow and snow aplenty, but it melts away faster than it accumulates, over the course of years.
So there is a zone of ice accumulation above the firn line, and a zone of ice ablation, below the firn line.
Of course, valley glaciers flow down below the firn line; so, for instance, we might reasonably place the Tioga firn line at 5,500 feet, but also reasonably expect to find that the valley glaciers, which formed "distributaries" for the ice constantly building above the firn line, to extend to significantly lower elevations. For instance, Tioga ice may have reached down the South Yuba to near the town of Washington, and down the North Fork American to near Humbug canyon. These locations are down near 2,500' in elevation.
One subtlety about the firn line is that it will run higher on slopes with southern exposures, and lower on slopes with northern exposures. Hence if it is 5,500' on southern exposures, it may be at only 5,000 feet on northern exposures. Now, our coniferous trees can be very sensitive indicators of climate, and microclimate.
Take the White Fir, Abies concolor. Its principal range or locus of occurrence is between 5'000 and 6'000 feet, where it often grows in nearly pure stands. Hence, it occurred to me away back when, the main population of White Fir could be used as a proxy for the lower, western extent of Tioga ice.
And this works out rather well. These White Firs often grow directly on Tioga-age glacial till.
But the White Fir is very sensitive to climate. On warm slopes with southern exposures one may not find any White Fir until one reaches 6,000', but on cold slopes, or especially, down in shady canyons or ravines, one can find the White Fir down to 4,000', and occasionally, still lower.
Blurring one's focus, then, one could take this approach: we lack direct evidence, let us say, of glaciation, at such-and-such a place; there is no till, no moraine, no exposed bedrock, and no glacial striae. We know, let us say, that the *main populations* of White Fir roughly coincide with the Tioga firn line, and we know that prior glaciations were more extensive. But those prior glaciations would have been subject to the usual microclimatic variations in their firn lines, higher on warmer slopes, lower on colder slopes and in shady canyons.
Hence one could take the tack of letting the White Fir once again stand as a proxy for these older firn lines, not in its principal locus of population, but in its western outliers. These more western, straggling populations of White Fir could help mark the extent of the earlier glaciations.
In "Mudflows, Incorporated" I described the sequence of andesitic lahars capping Moody Ridge. The top of the ridge, the top of these mudflows, is just above the 4,160-foot contour. A goodly number of White Firs grow up there, where the gentle slopes of the uplands trap cold air at night. On the adjacent south-facing slopes, however, dropping away into the North Fork, cold air flows away freely, and the White Fir disappears; whereas on the also-adjacent north-facing slopes, the White Fir remains an important component of the forest.
I made these observations in August of 1975, at which time I also found one glacial erratic, only a little below the summit of Moody Ridge, on the northern slopes, facing the freeway, I-80, and Canyon Creek. The erratic was a lone boulder of granite, six feet long, the one and only boulder of granite among ten thousand boulders of andesite.
The bedrock in this area is all serpentine and metamorphic rock of various stripes; whereas the nearest body of granite is ten miles away to the northeast. Hence to see granite is to see something quite out-of-place. There is very little to no granite involved in the ancient Eocene river channels in this area, either (for, the subtropical climate which prevailed then seems to have acted to rot whatever granite boulders there may have been in the sediments, into sand and clay).
Now, I am a cautious man. I could not discount the possibility that one of the andesitic mudflows, which predated the glaciations of the Pleistocene, had itself swept up this granite boulder, and carried it down here to Moody Ridge.
Were I to accept the boulder at face value, as a glacial erratic, I would have to accept that a valley glacier came down Canyon Creek itself, and that this valley glacier was 500 feet thick or more.
I hoped to find other erratics, and bodies of till, but I did not.
It happens that the upland surface of Moody Ridge resumes to the northeast, on nearby Casa Loma Ridge, less than a mile away. Between the two is a gap or pass, which is directly above the Eocene-age "Nary Red" channel. There is, then, a thicker-than-usual section of the "Young Volcanics" of the Superjacent Series here, filling the old Nary Red valley.
It would make sense that a valley glacier, flowing down Canyon Creek, might have helped create this gap, or pass, in the ridge dividing Canyon Creek from the North Fork canyon.
But I am a cautious man. I had noted, in 1975, that in the Gold Run area, these same Young Volcanics had been stripped away, exposing the Eocene river channel of the Tertiary Yuba, below. What erosive mechanism could account for the disappearance of two or three hundred feet of rhyolite ash beds and andesitic lahars? Could my putative pre-Tioga Canyon Creek glacier have been at work in Gold Run?
I never liked *that* idea, but, being a cautious man, I have still not ruled it out. My own instinct was then, and remains now, that the weakness of the volcanic layers, combined with the beyond-normal quantity of groundwater within the broad confines of the Tertiary river valley, had somehow acted to remove the volcanics.
I imagined the Tertiary channel to contain beyond-normal groundwater partly because the underlying bedrock of the Subjacent Series would have itself tended to feed groundwater towards the center of the ancient valley.
But if I apply this rather diffuse model to the Nary Red channel, between Moody Ridge and Casa Loma Ridge, then why invoke glaciers at all? The mysterious pass could be the "same old story" of already-weak volcanic strata further weakened by an excess of groundwater.
And one lone granite boulder could not be enough to demonstrate a robust Canyon Creek valley glacier extending west to, say, between the Alta and Dutch Flat exits on I-80. No, one strange boulder from a strange land is not nearly enough.
There were various other clues, though, which suggested that such a glacier had existed: on the northeast end of Moody Ridge, cliffs of the "cement stratum" of andesitic mudflow are exposed. This a rarity, for, despite the seeming toughness of the Cement Stratum, it is very rarely directly exposed, below and west of the Tioga ice. Higher and to the east this same stratum, or its close analogues, are wildly well-exposed. But here, near the 4,000-foot contour, soil-forming processes outpace erosion, and keep the cement stratum well-hidden. Only the very steepest slopes, subject to mass wasting in the form of minor landslides and slumps, exhibit real outcrops, and these outcrops are typically scattered and small, and do not convince one that one is even seeing the Cement Stratum (the outcrops can easily look like mere boulders, not the massive and undissected lahar itself).
This tendency of the Young Volcanics, even in their most resistant strata, to hide themselves beneath a mantle of soil, is frustrating. Roadcuts are often the only way one can assure oneself just what is what, down here, below and west of the Tioga ice. In particular, the old strata of rhyolite ash, beneath the andesitic lahars, are almost never directly exposed. The rhyolite ash is not only covered by deep soils, but boulders of andesite have rolled down from the lahars above, so all one sees are these andesitic boulders, not the rhyolite itself.
Hence it seemed potentially significant that actual cliffs of the Cement Stratum are exposed on the northeast prow of Moody Ridge, facing directly into the gap or pass above the Eocene channel. I also noted, in 1975, that minor outcrops of the underlying rhyolite ash exist, also facing northeast across this same Eocene channel.
In 1976, while exploring Green Valley, I found huge boulders of this same stratum of rhyolite ash (it is the closest of all the local strata of rhyolite ash, to being a bona fide welded tuff), well above the river, concentrated just where a ravine leaves the steep slopes of serpentine, above, for the moderate slopes of glacial outwash, below. This ravine heads up in this same Eocene-age Nary Red Channel.
But what mechanism could have brought these huge boulders over a mile from their source, into Green Valley?
To me it seemed extremely likely that the rare cliffs of the Cement Stratum, the rare outcrop of the Welded Tuff, and the very very peculiar "region of giant tuff boulders" in Green Valley, all pointed to glacial ice flowing down Canyon Creek, and breaking out of the creek's own proper valley to flow south into the North Fork canyon. It is not impossible that the ice made it all the way down to the river, but if the Canyon Creek glacier were of *that* magnitude, why, the North Fork glacier itself could have reached down to Green Valley.
But I am a cautious man. If there was a Canyon Creek glacier big enough to rip through the Nary Red pass, in effect, creating the pass, and big enough to bulldoze huge blocks of rhyolite ash, fifteen feet through, down into Green Valley, then where are the moraines, and if no moraines are left, from the long blurring of erosion, where is the till? I could find none.
That I could find no till, and I still can't find any to this day, does not mean it is not here. It could be quite well-disguised. For instance: almost all of Canyon Creek to the east and upstream, up-ice, down which my putative glacier would have flowed, is incised into the Young Volcanics. Now, it is reasonable to expect that this ice was flowing from points still farther east, where there is granite exposed. So, if there is till from this glacier, there could be, and maybe should be, granite boulders in that till.
On the other hand, suppose very very few granite boulders were along for the ride, in the Canyon Creek glacier; the glacier would in any case have been quarrying the andesitic lahars, and whatever tills are left, will be made of andesitic material, and, most problematically, these andesitic tills will be resting, quite often, directly upon andesitic lahars, which in turn are subject to deep soil formation, so that one sees a smattering of andesitic boulders embedded in soil, and from experience one deduces that under that soil is the lahar itself.
But one could deduce wrongly; that same smattering of andesitic boulders embedded in soil could quite easily be a glacial till, perhaps only a few feet thick, mantling the andesitic lahar underneath.
Yesterday I went in search of that granite boulder I saw back in 1975. I also wished to use GPS to identify the elevation of the top of the Cement Stratum.
I did not find the boulder, but the steep slope to which it clung was logged in 1977 and 1978, and bulldozed skid trails criss-cross the steep slopes. Countless tons of topsoil have been displaced due to these 1977-78 skid trails. Apparently we Americans are so rich in soil, we can just throw it away.
I walked to the top of the northeast-facing cliffs of the Cement Stratum, and GPS showed the elevation to be about 4010'. Above the Cement Stratum is my Stratum of Big Boulders, and I followed up the spine of the ridge into this higher layer. This Stratum of Big Boulders seems to be, really, just the basal part of the Stratum of Rotten Mudflow, which forms the uppermost lahar in the andesitic sequence, in this immediate area.
I had walked this bouldery spine many times since 1975, but yesterday I was very pleased to find something new: a small granite boulder, perhaps two to three feet in diameter, visibly weathered and old-looking, compared to the Tioga-age granite erratics one often sees farther east and higher in elevation, as for instance near Emigrant Gap.
So. Granite Boulder #2. Of course, there is still nothing to show that it was not brought down with a lahar, that it was a glacier what done it, but I have never yet seen a granite boulder embedded in a lahar, here at Moody Ridge. They do exist elsewhere, for instance, a little west of Blue Canyon, along the railroad, are some granite boulders embedded in a lahar; and although rare, I have seen a few here and there, in the higher elevations.
I was excited to find Boulder #2. I dropped down the north side, off the bouldery spine of the ridge, and followed skid trails down to Moody Ridge Road. I examined hundreds of boulders torn up by the logging, all andesite. And then I found Granite Boulder #3.
It looked very much as I recalled Granite Boulder #1, which I last saw in 1976 or 1977, being about six or eight feet long, and four or five feet thick. However, it was not in the same place, and was pretty clearly in its natural spot, undisturbed by skid trails. It was so well covered in moss I could not be sure it was granite, but, kicking away the moss, I was able to break off a dirty flake a foot across, and then break that flake, and I saw that, yes, it is granite.
Having observed three granite boulders in the near vicinity of the Nary Red pass, I am not so cautious, now, and I declare that:
*******
Once, if not many times, a glacier flowed down Canyon Creek, and once or several times this glacier was at least 500 feet thick, or, more pertinently, its top was at least as high as 4100' in elevation, near Moody Ridge. This glacier (or glaciers) broke through the ridge dividing Canyon Creek from the North Fork, creating the Nary Red Pass, and bulldozing huge blocks of rhyolite tuff into Green Valley. This glacier also broke out of Canyon Creek to the north, deepening the pass or gap near Lake Alta, and leaving the rare outcrops of rhyolite tuff exposed, near that lake. From the degree of weathering of the granite boulders, and the degree of weathering of the rhyolite boulders in Green Valley, and the degree of weathering of the rhyolite outcrops near Lake Alta, and the degree of weathering of the rhyolite outcrops flanking the Nary Red Pass on Moody Ridge, all of which degrees suggesting age but not "great age," I attribute the most recent Canyon Creek glacier to the Tahoe II glaciation, of approximately 65,000 years ago.
*******
If not Tahoe II, then to Tahoe I, ~130,000 years ago, do I turn. It is quite possible that several distinct glaciers broke through these passes, for instance, the Sherwin Glaciation of about 800,000 years ago, or the McGee Creek of ~1.3 million years ago; but I cannot accept that either of these older glaciations could have left these fairly sound and only slightly weathered granite boulders.
Why, one might ask, was this Canyon Creek glacier so eager to break out of the confines of Canyon Creek? I answer, because the valley of Canyon Creek narrows to a gorge between the Alta and Dutch Flat exits on I-80. This would have inhibited passage of the ice, which would have backed up upon itself, deepening until it was able to break through the two divides.
Actually, both passes, the one near Moody Ridge and the one near Lake Alta, are linked to the same Eocene-age (and also intervolcanic), Nary Red Channel. The southern pass connects Canyon Creek to the North Fork American, the northern, "Lake Alta" pass connects Canyon Creek to the Bear River.
After discovering Granite Boulder #3 I walked north to Casa Loma Ridge, and climbed it, searching for more granite erratics, but finding none. I used my GPS to locate the top of the Cement Stratum at about 4020', or about ten feet higher than at the northeast corner of Moody Ridge.
Although I have walked around Lake Alta and explored nearby ridges and swales several times over the years, I have never seen a granite boulder there. If my hypothesis about a Canyon Creek glacier breaking through both passes is correct, there ought to be at least one or two such granite boulders kicking around over that way.
I guess it's time for a fresh look.
OK, that's all for now folks, except, I will provide a limited bibliography, of works I have consulted over the years, below. For some of the best and most recent discussions of landscape evolution here in the Sierra, see the papers by Greg Stock and John Wakabayashi. My friend L.A. James has also made very significant contributions, although I disagree with his interpretation of the Tioga glaciation, among other things.
Bibliography:
Bateman, P.C. and Wahrhaftig, C., 1966. Geology of the Sierra Nevada. In: Geology of Northern California, Calif. Div. Mines and Geol., Bull. 190, pp.107-172.
Birkeland, P.W., 1964. Pleistocene glaciation of the northern Sierra Nevada, north of Lake Tahoe, California. J. Geol., 72: 810-825.
Blackwelder, E., 1931. Pleistocene glaciation in the Sierra Nevada and the Basin Ranges. Geol. Soc. Am. Bull., 42: 865-922.
Brewer, W.H., 1966. Up and down California in 1860-1864. Reprinted in: F.P. Farquhar (Editor), 3rd Ed. Univ. Calif. Press, Berkeley.
James, L.A., Harbor, J., Fabel, D., Dahms, D. and Elmore, D., 2002. Late Pleistocene Glaciations in the Northwestern Sierra Nevada, California. Quat Res., 57(3): .
Lindgren, W., 1897. Description of the gold belt: description of the Truckee Quadrange, California. U.S. Geol. Surv. Geol. Atlas, Folio 39; 1:125,000; 8 pp.
Lindgren, W., 1900. Description of the Colfax Quadrangle, California. U.S. Geol. Surv., Geologic Atlas, Folio 66; 1:125,000; 10 pp.
Lindgren, W., 1911. Tertiary Gravels of the Sierra Nevada of California. U.S. Geol. Surv. Prof. Pap. 73, 226 pp.
Matthes, F., 1930. Geologic History of Yosemite Valley. U.S. Geol. Surv. Prof. Pap. 160, Wash, D.C., 137 pp.
Muir, J., 1873a. Discovery of glaciers in Sierra Nevada. Am. Jour. Sci., 3rd series, 5: 69-71.
Muir, J., 1873b. Explorations in the great Tuolumne Cañon, Overland Monthly. Reprinted in: A. Gilliam (Editor), Voices for the Earth: A Treasury of the Sierra Club Bulletin. Sierra Club Books, San Francisco, CA.
Russell, I.C., 1889. Quaternary History of Mono Valley, California. U.S. Geol. Surv. 8th Ann. Rpt., Pt.1, Wash., D.C., pp. 261-394.
Stock GM, Anderson RS, Finkel RC. 2004. Pace of landscape evolution in the Sierra Nevada, California, revealed by cosmogenic dating of cave sediments. Geology 32: 193-196.
Wakabayashi J., Sawyer TL. 2001. Stream incision, tectonics, uplift, and evof the Sierra Nevada, California. Journal of Geology 109: 539-562.
Whitney, J.D., 1865. Geology of the Sierra Nevada. Geologic Survey of California, Geology, Vol.1, Calif. Legislature, CA, 498 pp.
Yeend, W.E., 1974. Gold-bearing Gravel of the Ancestral Yuba River, Sierra Nevada, California. U.S. Geol. Surv. Prof. Paper 772, Wash., D.C., 44 pp.
The rarest glacial erratics are to the west, away from the high country, away from any obvious evidence of glaciation. They are old; but how old?
From about 5,500 feet in elevation and up, one sees abundant signs of the most recent, "Tioga" glaciation, which ended a scant 12,000 years ago. But the Tioga is only one of many. It is thought that, over the past 800,000 years, glacial climates have dominated, with warm "interglacial" climatic episodes (like today's climate) comprising as little as 10% of the total. And it has long been understood that the most recent glaciation of magnitude, the Tioga, was preceded by earlier, more intense glaciations.
By 1975 I was much on the alert for signs of these older glaciations. Such signs are not too easy to find, here on the west slope of the Sierra, where very abundant rainfall and snowfall tend to blur moraines into formless glacial till, and eventually, strip away that till altogether.
When glaciation takes place, there is a "firn line," usually imagined to be a contour line of fixed elevation. Above this elevation, snow accumulates into glacial ice; below this elevation, it may snow and snow aplenty, but it melts away faster than it accumulates, over the course of years.
So there is a zone of ice accumulation above the firn line, and a zone of ice ablation, below the firn line.
Of course, valley glaciers flow down below the firn line; so, for instance, we might reasonably place the Tioga firn line at 5,500 feet, but also reasonably expect to find that the valley glaciers, which formed "distributaries" for the ice constantly building above the firn line, to extend to significantly lower elevations. For instance, Tioga ice may have reached down the South Yuba to near the town of Washington, and down the North Fork American to near Humbug canyon. These locations are down near 2,500' in elevation.
One subtlety about the firn line is that it will run higher on slopes with southern exposures, and lower on slopes with northern exposures. Hence if it is 5,500' on southern exposures, it may be at only 5,000 feet on northern exposures. Now, our coniferous trees can be very sensitive indicators of climate, and microclimate.
Take the White Fir, Abies concolor. Its principal range or locus of occurrence is between 5'000 and 6'000 feet, where it often grows in nearly pure stands. Hence, it occurred to me away back when, the main population of White Fir could be used as a proxy for the lower, western extent of Tioga ice.
And this works out rather well. These White Firs often grow directly on Tioga-age glacial till.
But the White Fir is very sensitive to climate. On warm slopes with southern exposures one may not find any White Fir until one reaches 6,000', but on cold slopes, or especially, down in shady canyons or ravines, one can find the White Fir down to 4,000', and occasionally, still lower.
Blurring one's focus, then, one could take this approach: we lack direct evidence, let us say, of glaciation, at such-and-such a place; there is no till, no moraine, no exposed bedrock, and no glacial striae. We know, let us say, that the *main populations* of White Fir roughly coincide with the Tioga firn line, and we know that prior glaciations were more extensive. But those prior glaciations would have been subject to the usual microclimatic variations in their firn lines, higher on warmer slopes, lower on colder slopes and in shady canyons.
Hence one could take the tack of letting the White Fir once again stand as a proxy for these older firn lines, not in its principal locus of population, but in its western outliers. These more western, straggling populations of White Fir could help mark the extent of the earlier glaciations.
In "Mudflows, Incorporated" I described the sequence of andesitic lahars capping Moody Ridge. The top of the ridge, the top of these mudflows, is just above the 4,160-foot contour. A goodly number of White Firs grow up there, where the gentle slopes of the uplands trap cold air at night. On the adjacent south-facing slopes, however, dropping away into the North Fork, cold air flows away freely, and the White Fir disappears; whereas on the also-adjacent north-facing slopes, the White Fir remains an important component of the forest.
I made these observations in August of 1975, at which time I also found one glacial erratic, only a little below the summit of Moody Ridge, on the northern slopes, facing the freeway, I-80, and Canyon Creek. The erratic was a lone boulder of granite, six feet long, the one and only boulder of granite among ten thousand boulders of andesite.
The bedrock in this area is all serpentine and metamorphic rock of various stripes; whereas the nearest body of granite is ten miles away to the northeast. Hence to see granite is to see something quite out-of-place. There is very little to no granite involved in the ancient Eocene river channels in this area, either (for, the subtropical climate which prevailed then seems to have acted to rot whatever granite boulders there may have been in the sediments, into sand and clay).
Now, I am a cautious man. I could not discount the possibility that one of the andesitic mudflows, which predated the glaciations of the Pleistocene, had itself swept up this granite boulder, and carried it down here to Moody Ridge.
Were I to accept the boulder at face value, as a glacial erratic, I would have to accept that a valley glacier came down Canyon Creek itself, and that this valley glacier was 500 feet thick or more.
I hoped to find other erratics, and bodies of till, but I did not.
It happens that the upland surface of Moody Ridge resumes to the northeast, on nearby Casa Loma Ridge, less than a mile away. Between the two is a gap or pass, which is directly above the Eocene-age "Nary Red" channel. There is, then, a thicker-than-usual section of the "Young Volcanics" of the Superjacent Series here, filling the old Nary Red valley.
It would make sense that a valley glacier, flowing down Canyon Creek, might have helped create this gap, or pass, in the ridge dividing Canyon Creek from the North Fork canyon.
But I am a cautious man. I had noted, in 1975, that in the Gold Run area, these same Young Volcanics had been stripped away, exposing the Eocene river channel of the Tertiary Yuba, below. What erosive mechanism could account for the disappearance of two or three hundred feet of rhyolite ash beds and andesitic lahars? Could my putative pre-Tioga Canyon Creek glacier have been at work in Gold Run?
I never liked *that* idea, but, being a cautious man, I have still not ruled it out. My own instinct was then, and remains now, that the weakness of the volcanic layers, combined with the beyond-normal quantity of groundwater within the broad confines of the Tertiary river valley, had somehow acted to remove the volcanics.
I imagined the Tertiary channel to contain beyond-normal groundwater partly because the underlying bedrock of the Subjacent Series would have itself tended to feed groundwater towards the center of the ancient valley.
But if I apply this rather diffuse model to the Nary Red channel, between Moody Ridge and Casa Loma Ridge, then why invoke glaciers at all? The mysterious pass could be the "same old story" of already-weak volcanic strata further weakened by an excess of groundwater.
And one lone granite boulder could not be enough to demonstrate a robust Canyon Creek valley glacier extending west to, say, between the Alta and Dutch Flat exits on I-80. No, one strange boulder from a strange land is not nearly enough.
There were various other clues, though, which suggested that such a glacier had existed: on the northeast end of Moody Ridge, cliffs of the "cement stratum" of andesitic mudflow are exposed. This a rarity, for, despite the seeming toughness of the Cement Stratum, it is very rarely directly exposed, below and west of the Tioga ice. Higher and to the east this same stratum, or its close analogues, are wildly well-exposed. But here, near the 4,000-foot contour, soil-forming processes outpace erosion, and keep the cement stratum well-hidden. Only the very steepest slopes, subject to mass wasting in the form of minor landslides and slumps, exhibit real outcrops, and these outcrops are typically scattered and small, and do not convince one that one is even seeing the Cement Stratum (the outcrops can easily look like mere boulders, not the massive and undissected lahar itself).
This tendency of the Young Volcanics, even in their most resistant strata, to hide themselves beneath a mantle of soil, is frustrating. Roadcuts are often the only way one can assure oneself just what is what, down here, below and west of the Tioga ice. In particular, the old strata of rhyolite ash, beneath the andesitic lahars, are almost never directly exposed. The rhyolite ash is not only covered by deep soils, but boulders of andesite have rolled down from the lahars above, so all one sees are these andesitic boulders, not the rhyolite itself.
Hence it seemed potentially significant that actual cliffs of the Cement Stratum are exposed on the northeast prow of Moody Ridge, facing directly into the gap or pass above the Eocene channel. I also noted, in 1975, that minor outcrops of the underlying rhyolite ash exist, also facing northeast across this same Eocene channel.
In 1976, while exploring Green Valley, I found huge boulders of this same stratum of rhyolite ash (it is the closest of all the local strata of rhyolite ash, to being a bona fide welded tuff), well above the river, concentrated just where a ravine leaves the steep slopes of serpentine, above, for the moderate slopes of glacial outwash, below. This ravine heads up in this same Eocene-age Nary Red Channel.
But what mechanism could have brought these huge boulders over a mile from their source, into Green Valley?
To me it seemed extremely likely that the rare cliffs of the Cement Stratum, the rare outcrop of the Welded Tuff, and the very very peculiar "region of giant tuff boulders" in Green Valley, all pointed to glacial ice flowing down Canyon Creek, and breaking out of the creek's own proper valley to flow south into the North Fork canyon. It is not impossible that the ice made it all the way down to the river, but if the Canyon Creek glacier were of *that* magnitude, why, the North Fork glacier itself could have reached down to Green Valley.
But I am a cautious man. If there was a Canyon Creek glacier big enough to rip through the Nary Red pass, in effect, creating the pass, and big enough to bulldoze huge blocks of rhyolite ash, fifteen feet through, down into Green Valley, then where are the moraines, and if no moraines are left, from the long blurring of erosion, where is the till? I could find none.
That I could find no till, and I still can't find any to this day, does not mean it is not here. It could be quite well-disguised. For instance: almost all of Canyon Creek to the east and upstream, up-ice, down which my putative glacier would have flowed, is incised into the Young Volcanics. Now, it is reasonable to expect that this ice was flowing from points still farther east, where there is granite exposed. So, if there is till from this glacier, there could be, and maybe should be, granite boulders in that till.
On the other hand, suppose very very few granite boulders were along for the ride, in the Canyon Creek glacier; the glacier would in any case have been quarrying the andesitic lahars, and whatever tills are left, will be made of andesitic material, and, most problematically, these andesitic tills will be resting, quite often, directly upon andesitic lahars, which in turn are subject to deep soil formation, so that one sees a smattering of andesitic boulders embedded in soil, and from experience one deduces that under that soil is the lahar itself.
But one could deduce wrongly; that same smattering of andesitic boulders embedded in soil could quite easily be a glacial till, perhaps only a few feet thick, mantling the andesitic lahar underneath.
Yesterday I went in search of that granite boulder I saw back in 1975. I also wished to use GPS to identify the elevation of the top of the Cement Stratum.
I did not find the boulder, but the steep slope to which it clung was logged in 1977 and 1978, and bulldozed skid trails criss-cross the steep slopes. Countless tons of topsoil have been displaced due to these 1977-78 skid trails. Apparently we Americans are so rich in soil, we can just throw it away.
I walked to the top of the northeast-facing cliffs of the Cement Stratum, and GPS showed the elevation to be about 4010'. Above the Cement Stratum is my Stratum of Big Boulders, and I followed up the spine of the ridge into this higher layer. This Stratum of Big Boulders seems to be, really, just the basal part of the Stratum of Rotten Mudflow, which forms the uppermost lahar in the andesitic sequence, in this immediate area.
I had walked this bouldery spine many times since 1975, but yesterday I was very pleased to find something new: a small granite boulder, perhaps two to three feet in diameter, visibly weathered and old-looking, compared to the Tioga-age granite erratics one often sees farther east and higher in elevation, as for instance near Emigrant Gap.
So. Granite Boulder #2. Of course, there is still nothing to show that it was not brought down with a lahar, that it was a glacier what done it, but I have never yet seen a granite boulder embedded in a lahar, here at Moody Ridge. They do exist elsewhere, for instance, a little west of Blue Canyon, along the railroad, are some granite boulders embedded in a lahar; and although rare, I have seen a few here and there, in the higher elevations.
I was excited to find Boulder #2. I dropped down the north side, off the bouldery spine of the ridge, and followed skid trails down to Moody Ridge Road. I examined hundreds of boulders torn up by the logging, all andesite. And then I found Granite Boulder #3.
It looked very much as I recalled Granite Boulder #1, which I last saw in 1976 or 1977, being about six or eight feet long, and four or five feet thick. However, it was not in the same place, and was pretty clearly in its natural spot, undisturbed by skid trails. It was so well covered in moss I could not be sure it was granite, but, kicking away the moss, I was able to break off a dirty flake a foot across, and then break that flake, and I saw that, yes, it is granite.
Having observed three granite boulders in the near vicinity of the Nary Red pass, I am not so cautious, now, and I declare that:
*******
Once, if not many times, a glacier flowed down Canyon Creek, and once or several times this glacier was at least 500 feet thick, or, more pertinently, its top was at least as high as 4100' in elevation, near Moody Ridge. This glacier (or glaciers) broke through the ridge dividing Canyon Creek from the North Fork, creating the Nary Red Pass, and bulldozing huge blocks of rhyolite tuff into Green Valley. This glacier also broke out of Canyon Creek to the north, deepening the pass or gap near Lake Alta, and leaving the rare outcrops of rhyolite tuff exposed, near that lake. From the degree of weathering of the granite boulders, and the degree of weathering of the rhyolite boulders in Green Valley, and the degree of weathering of the rhyolite outcrops near Lake Alta, and the degree of weathering of the rhyolite outcrops flanking the Nary Red Pass on Moody Ridge, all of which degrees suggesting age but not "great age," I attribute the most recent Canyon Creek glacier to the Tahoe II glaciation, of approximately 65,000 years ago.
*******
If not Tahoe II, then to Tahoe I, ~130,000 years ago, do I turn. It is quite possible that several distinct glaciers broke through these passes, for instance, the Sherwin Glaciation of about 800,000 years ago, or the McGee Creek of ~1.3 million years ago; but I cannot accept that either of these older glaciations could have left these fairly sound and only slightly weathered granite boulders.
Why, one might ask, was this Canyon Creek glacier so eager to break out of the confines of Canyon Creek? I answer, because the valley of Canyon Creek narrows to a gorge between the Alta and Dutch Flat exits on I-80. This would have inhibited passage of the ice, which would have backed up upon itself, deepening until it was able to break through the two divides.
Actually, both passes, the one near Moody Ridge and the one near Lake Alta, are linked to the same Eocene-age (and also intervolcanic), Nary Red Channel. The southern pass connects Canyon Creek to the North Fork American, the northern, "Lake Alta" pass connects Canyon Creek to the Bear River.
After discovering Granite Boulder #3 I walked north to Casa Loma Ridge, and climbed it, searching for more granite erratics, but finding none. I used my GPS to locate the top of the Cement Stratum at about 4020', or about ten feet higher than at the northeast corner of Moody Ridge.
Although I have walked around Lake Alta and explored nearby ridges and swales several times over the years, I have never seen a granite boulder there. If my hypothesis about a Canyon Creek glacier breaking through both passes is correct, there ought to be at least one or two such granite boulders kicking around over that way.
I guess it's time for a fresh look.
OK, that's all for now folks, except, I will provide a limited bibliography, of works I have consulted over the years, below. For some of the best and most recent discussions of landscape evolution here in the Sierra, see the papers by Greg Stock and John Wakabayashi. My friend L.A. James has also made very significant contributions, although I disagree with his interpretation of the Tioga glaciation, among other things.
Bibliography:
Bateman, P.C. and Wahrhaftig, C., 1966. Geology of the Sierra Nevada. In: Geology of Northern California, Calif. Div. Mines and Geol., Bull. 190, pp.107-172.
Birkeland, P.W., 1964. Pleistocene glaciation of the northern Sierra Nevada, north of Lake Tahoe, California. J. Geol., 72: 810-825.
Blackwelder, E., 1931. Pleistocene glaciation in the Sierra Nevada and the Basin Ranges. Geol. Soc. Am. Bull., 42: 865-922.
Brewer, W.H., 1966. Up and down California in 1860-1864. Reprinted in: F.P. Farquhar (Editor), 3rd Ed. Univ. Calif. Press, Berkeley.
James, L.A., Harbor, J., Fabel, D., Dahms, D. and Elmore, D., 2002. Late Pleistocene Glaciations in the Northwestern Sierra Nevada, California. Quat Res., 57(3): .
Lindgren, W., 1897. Description of the gold belt: description of the Truckee Quadrange, California. U.S. Geol. Surv. Geol. Atlas, Folio 39; 1:125,000; 8 pp.
Lindgren, W., 1900. Description of the Colfax Quadrangle, California. U.S. Geol. Surv., Geologic Atlas, Folio 66; 1:125,000; 10 pp.
Lindgren, W., 1911. Tertiary Gravels of the Sierra Nevada of California. U.S. Geol. Surv. Prof. Pap. 73, 226 pp.
Matthes, F., 1930. Geologic History of Yosemite Valley. U.S. Geol. Surv. Prof. Pap. 160, Wash, D.C., 137 pp.
Muir, J., 1873a. Discovery of glaciers in Sierra Nevada. Am. Jour. Sci., 3rd series, 5: 69-71.
Muir, J., 1873b. Explorations in the great Tuolumne Cañon, Overland Monthly. Reprinted in: A. Gilliam (Editor), Voices for the Earth: A Treasury of the Sierra Club Bulletin. Sierra Club Books, San Francisco, CA.
Russell, I.C., 1889. Quaternary History of Mono Valley, California. U.S. Geol. Surv. 8th Ann. Rpt., Pt.1, Wash., D.C., pp. 261-394.
Stock GM, Anderson RS, Finkel RC. 2004. Pace of landscape evolution in the Sierra Nevada, California, revealed by cosmogenic dating of cave sediments. Geology 32: 193-196.
Wakabayashi J., Sawyer TL. 2001. Stream incision, tectonics, uplift, and evof the Sierra Nevada, California. Journal of Geology 109: 539-562.
Whitney, J.D., 1865. Geology of the Sierra Nevada. Geologic Survey of California, Geology, Vol.1, Calif. Legislature, CA, 498 pp.
Yeend, W.E., 1974. Gold-bearing Gravel of the Ancestral Yuba River, Sierra Nevada, California. U.S. Geol. Surv. Prof. Paper 772, Wash., D.C., 44 pp.
Wednesday, November 15, 2006
Mudflows, Incorporated
[written November 15, 2006]
What a glorious season! Indian Summer grading into the storms of winter. The Black Oaks, Bigleaf Maples, Pacific Dogwoods, Blue Elderberries, Thimbleberries, Bracken ferns, and all manner of deciduous plants are blushing into all manner of golds and reds and purples and browns. Wow.
This has been a time of no expeditions down into the canyon, but many short hikes near my home, on Moody Ridge, near Dutch Flat. I have decided to make a precise geological map of Green Valley, a Gold-Rush-era mining camp of huge proportions, down along the North Fork, below Moody Ridge to the south. I actually began work on this map years ago, but now I will collate results, and also use GPS to exactly locate the boundaries of the various Quaternary units and bedrock structures in and around Green Valley.
I decided, too, that I would map Moody Ridge, for a big part of the story I want to tell has to do with the actual incision of the North Fork canyon; when it began, how quickly it proceeded, and so on.
Now, it happens that all the main ridges in this area, about half-way between the great plains of the Sacramento Valley, and the frozen summits of the Sierra, heh heh--in this area, I repeat, at around four thousand feet in elevation--it happens that all the main ridges are "accordant," that is, their summits are all at very much the same elevations, and these summits all slope very very gently to the southwest.
Moody Ridge is one of these accordant ridges. They are without exception relics of the Pliocene-era volcanic mudflow plateau which covered all this region, for many dozens of miles south and north. The plateau extended almost to the Tuolumne River on the south, and on up through the Feather River country to the north. It was pervasive, huge.
But then a gigantic slab of the earth's crust was tilted up like a trap door, a slab four hundred miles long and about one hundred miles wide; and we call this slab the Sierra Nevada.
It is worth noting that the crest of the Sierra itself is self-accordant, as it were, in that the many summits gradually increase in elevation, southward; we go from a paltry 8000' in the northernmost Sierra, to 9000' near Donner Pass, 10,000 feet at Highway 50, 13,000' at Tioga Pass near Yosemite, and 14,000' at the Palisades and Mt. Whitney itself, away down by the great canyon of the Kern, that strange Sierran canyon, unlike all others, which parallels the crest, instead of running away at a right angle.
At any rate, this self-accordant, smoothly-rising-to-the-south Sierra crest suggests that more uplift has occurred in the south than in the north. It is thought that there has been 10,000 feet of fairly recent uplift near Mt. Whitney, but only 4,000 feet, or thereabouts, near Donner Pass. There is some debate about Sierran uplift, its timing, and its magnitude, but I cannot go into the details now.
Here in the Dutch Flat area, the general pattern obtains, and all the major canyons trend from northeast to southwest, as do the long axes of all the ridges dividing such canyons; and Moody Ridge is among these many accordant ridges. If one had a giant ruler and laid it across the North Fork canyon, on a right angle, from Moody Ridge, to, say, the accordant Giant Gap Ridge, across the canyon to the southeast, one would find that that ruler was about dead level.
One can actually fit a plane to these accordant ridges, and thus restore implicitly the surface of the Pliocene andesitic mudflow plateau. I have done experiments with such plane-fittings using software which allows me to create virtual landscapes, based upon USGS Digital Elevation Model data, for this area--very very accurate models in which elevations are known on a square grid of 30-meter intervals. The software requires me to express the planes I use for fitting in terms of their surface normals and distance form the origin. It is a little cumbersome.
The Pliocene plateau sat atop the Sierran slab, and when the slab tilted up, the plateau tilted with it. There appears to have been about 4000' or 5000' of uplift at the Sierra crest near Donner Pass. It occurred over a few millions of years, and is still occurring. We shall have earthquakes which will thrown down many or all our old brick and stone buildings, in towns like Dutch Flat, Colfax, Grass Valley, and Nevada City.
So, the whole slab is tilted up like a trap door, sloping gently down to the southwest, and a system of "consequent" streams developed on the plateau; geomorphologists might say that the streams (the Feather, Yuba, Bear, American, etc.) are "consequent upon" the gently sloping surface. In other words, they incised their courses directly downhill, to the southwest.
Then came the Pleistocene, less than three million years ago, and glaciation seems to have spurred rapid incision of the canyons, so that they cut through the andesitic mudflow, cut through the rhyolite ash beneath it, cut through whatever river gravels etc. which may have been underneath that rhyolite ash, and then hit the bedrock, and just kept right on cutting, down and down and down.
So that, for instance, right here at the northeast end of Moody Ridge, the North Fork canyon began by cutting through 250 feet of mudflow (4200' to 3950'), then 50 feet of rhyolite ash (3950' to 3900'), then 2,100 feet of the Mesozoic serpentine of the Melones Fault Zone (3900' to 1800').
And all this happened within, let us imagine, the last four million years.
So with simple arithmetic we can express the *average* rate of incision, in, say, inches per thousand years, or small fractions of an inch, per year (nowadays geologists like to express incision in terms of millimeters/year; I like inches per thousand years, myself). We say, the canyon has incised itself 2,400 feet in 4 million years, and find the average rate to have been, then, 7.2 inches per thousand years, or .72 inches in a hundred years.
This is quite a rapid rate of incision. My own instinct is that it is slower than that, right now, and that it accelerates during glacial maxima, of which maxima there have been many, over the past few million years.
Now, the sources of the andesitic mudflows which had built up the plateau, over millions of years time, were volcanos near, or on, the present Sierra crest; so it is natural, and correct, to surmise that these mudflows are thicker near the crest, and that they thin as one gets farther and farther away from the crest.
A geologic map of this whole part of the Sierra confirms that surmise; if one focuses upon the mudflows, which are typically given some kind of orange or tan color on the map, one sees as it were the many accordant ridges, with the dendritic branches of the canyons dividing one patch of mudflow, one ridge, from the next; and the patches are larger and much concentrated in the middle and upper elevations, but become scarcer and smaller down lower in the foothills.
Nevertheless, to this day one can find andesitic mudflows which reached the Sacramento Valley itself. One is exposed along Sierra College Boulevard, near Rocklin, south of I-80.
All the above is prologue, then, to a simple question: given that the northeast end of Moody Ridge is capped by 250 feet of andesitic mudflows, how many different mudflows can be identified within this section?
At higher elevations, where recent glaciation has exposed huge expanses of mudflow, one sometimes obtains quite a good look at multiple different layers of andesitic mudflow. These would probably obtain the status of distinct named "formations," if a precise geologic map were made.
Since I aim to make a precise map here, it behooved me to go out hiking and walking and thrashing through the brush and try to establish exactly how many different mudflows exist, right here.
I was surprised to find only two, or possibly four, different mudflows within this 250-foot section.
From the summit of the ridge, at about 4200', down to about 4100', there is one mudflow, characterized by very rotten boulders of light brown and yellowish and tan andesite, embedded in a matrix of very light-colored, grey and tan andesitic (?) ash.
This stratum, of about one hundred feet in thickness, is well-exposed in a certain roadcut. The rotten boulders were cut in a perfect plane; it is quite amazing and even pretty, in its way, to see all these thousands of spheroidal andesite boulders, in cross-section. I hesitate to even call this stuff andesite, for it is so deeply weathered and rotten now, despite being the highest and youngest mudflow locally, that it simply cannot be the same rock as the very sound and solid boulders of the lower, older strata.
As one drops lower in the upper, rotten mudflow, there begins to be an admixture of real, sound, andesite boulders. And as one nears the base of the stratum, there is a discrete layer containing many large andesite boulders, perfectly sound, and in freshly-broken chunks this rock is seen to be dark grey to black, with small white flecks of feldspar, such as one should see in a proper andesite. These boulders range up to four feet in diameter. There are occasional very small fluvial deposits, or so they seem, within this Stratum of Big Boulders. The Stratum of Big Boulders is only about ten feet thick. It seems to grade directly into the Stratum of Rotten Mudflow above it, yet I am tempted to separate the two into distinct formations.
Immediately below the Stratum of Big Boulders, and extending from about 4100' down to 4000', is the Stratum of Cement. This is a classic andesitic mudflow, identical in appearance to many exposures in the higher elevations, such as on the very summit of Castle Peak, near Donner Pass. Boulders and cobbles of sound andesite, up to a couple feet in diameter but commonly less than one foot in diameter, and sometimes well-rounded, but often quite angular and only slightly rounded off, and all these boulders and cobbles are embedded in a light grey matrix of andesitic ash.
In this Stratum of Cement (for this mudflow looks much like a rough concrete) one can find the remains of branches and limbs of trees, and fragments of leaves and conifer needles. Usually the wood rotted away to nearly nothing and left a hollow, a perfect mold, in the mudflow; but sometimes one can find the punky remains of wood millions of years old, within these hollows.
I speak of the Cement Stratum here on the northeast end of Moody Ridge; elsewhere, and more typically, the same formation, or its close relatives, will not display any fossil organic material whatsoever.
On the other hand, near Donner Summit I myself found a perfectly-preserved impression of a Madrone leaf, in just such a mudflow stratum, a stratum which contained a thin layer of finer sediments; and in these fine sediments are many leaf fossils, mainly, though, fir needles, by their appearance. The Madrone leaf was quite a lucky find. Geologist David Lawler saw that the fossil found a proper home, with the paleontology people at U.C. Berkeley.
Back to the northeast corner of Moody Ridge: below the ~100-foot thick Cement Stratum is a very poorly-exposed stratum which for all the world looks like something intermediate between the out-and-out andesitic mudflow above, and the out-and-out rhyolite ash strata, below: it is a light-grey stratum of volcanic ash, perhaps andesitic ash, perhaps grading towards rhyolite in chemical composition, and embedded in this ash stratum are just a few cobbles and small boulders of sound andesite. The stratum appears to be about twenty or thirty feet thick, maybe a little more.
So, naming this the Intermediate Stratum, I have tentatively identified four distinct mudflows or "formations" in the global andesitic mudflow "cap" at the northeast end of Moody Ridge. Listing them in descending order, youngest first and oldest last, we have, then,
1. Stratum of Rotten Mudflow.
(unconformity?)
2. Stratum of Big Boulders.
(unconformity)
3. Stratum of Cement.
(unconformity)
4. Stratum of Intermediate Composition.
(unconformity)
rhyolite ash, fluvial deposits, several to many unconformities
(unconformity)
bedrock
I write "unconformity" wherever there has clearly been a break in the deposition, that is, many thousands of years, perhaps even a million years or several millions of years, could fit into any one of these unconformities. During those time periods the uppermost stratum was an erosion surface.
Between the Rotten Stratum and the Big Boulders Stratum I am not sure if an unconfomity exists. It could well be that the Stratum of Big Boulders is derived from, say, a few million years of erosion of the underlying Stratum of Cement. This erosion freed big boulders from their matrix as the fines washed away, and thus slowly concentrated these very slowly-eroding boulders at the surface. Then, as I imagine it, the Rotten Mudflow roared over the erosion surface of the Cement Stratum, and very likely swept up and entrained into its own messy mass many of these boulders. Being dense and heavy, they tended to remain at the bottom of the flow. Hence they remained concentrated, and hence the Stratum of Big Boulders.
Beneath the andesitic mudflows are various strata of rhyolite ash, in this area interbedded with volcano-fluvial deposits, since the Eocene-age Nary Red Channel is quite close by on the northeast. This ancient prevolcanic river channel, akin to those in Dutch Flat and Gold Run, was apparently never entirely blocked up by the rhyolite ash eruptions of the Oligocene and early Miocene, so the river continued to flow, but the erosion surfaces upstream were fairly well covered in volcanics, so most of the cobbles and sediments in the upper strata of the channel are of rhyolite.
However, the andesitic mudflows subsequently filled up the Nary Red Channel valley to overflowing, and that was that.
Well, I haven't been writing much lately, but I have been at least thinking about the North Fork, and its geology, and its trails, and so on. I have studied the geology of the Sierra for about forty years now. So far as my understanding of purely local geology goes, I find myself collating results as it were, re-examining my own observations and my readings and drawing new conclusions, of which I hope to wrote more in the future. For instance, I am about certain that in older glaciations, such as the Tahoe I and Tahoe II, of 130,000 and 65,000 years ago, ice came down Canyon Creek and broke through the divide just northeast of Moody Ridge, directly over the axis of the ancient Nary Red Channel (no coincidence, the dividing ridge was weaker there), and hung down the canyon wall at least a little ways towards Green Valley, all the while quarrying out the gigantic chunks of rhyolite ash which one finds, today, away down on the floor of Green Valley itself.
This patch of rhyolite mega-boulders is drastically out of place and will definitely appear on my precise map of Green Valley. It is one of the more interesting formations down there.
What a glorious season! Indian Summer grading into the storms of winter. The Black Oaks, Bigleaf Maples, Pacific Dogwoods, Blue Elderberries, Thimbleberries, Bracken ferns, and all manner of deciduous plants are blushing into all manner of golds and reds and purples and browns. Wow.
This has been a time of no expeditions down into the canyon, but many short hikes near my home, on Moody Ridge, near Dutch Flat. I have decided to make a precise geological map of Green Valley, a Gold-Rush-era mining camp of huge proportions, down along the North Fork, below Moody Ridge to the south. I actually began work on this map years ago, but now I will collate results, and also use GPS to exactly locate the boundaries of the various Quaternary units and bedrock structures in and around Green Valley.
I decided, too, that I would map Moody Ridge, for a big part of the story I want to tell has to do with the actual incision of the North Fork canyon; when it began, how quickly it proceeded, and so on.
Now, it happens that all the main ridges in this area, about half-way between the great plains of the Sacramento Valley, and the frozen summits of the Sierra, heh heh--in this area, I repeat, at around four thousand feet in elevation--it happens that all the main ridges are "accordant," that is, their summits are all at very much the same elevations, and these summits all slope very very gently to the southwest.
Moody Ridge is one of these accordant ridges. They are without exception relics of the Pliocene-era volcanic mudflow plateau which covered all this region, for many dozens of miles south and north. The plateau extended almost to the Tuolumne River on the south, and on up through the Feather River country to the north. It was pervasive, huge.
But then a gigantic slab of the earth's crust was tilted up like a trap door, a slab four hundred miles long and about one hundred miles wide; and we call this slab the Sierra Nevada.
It is worth noting that the crest of the Sierra itself is self-accordant, as it were, in that the many summits gradually increase in elevation, southward; we go from a paltry 8000' in the northernmost Sierra, to 9000' near Donner Pass, 10,000 feet at Highway 50, 13,000' at Tioga Pass near Yosemite, and 14,000' at the Palisades and Mt. Whitney itself, away down by the great canyon of the Kern, that strange Sierran canyon, unlike all others, which parallels the crest, instead of running away at a right angle.
At any rate, this self-accordant, smoothly-rising-to-the-south Sierra crest suggests that more uplift has occurred in the south than in the north. It is thought that there has been 10,000 feet of fairly recent uplift near Mt. Whitney, but only 4,000 feet, or thereabouts, near Donner Pass. There is some debate about Sierran uplift, its timing, and its magnitude, but I cannot go into the details now.
Here in the Dutch Flat area, the general pattern obtains, and all the major canyons trend from northeast to southwest, as do the long axes of all the ridges dividing such canyons; and Moody Ridge is among these many accordant ridges. If one had a giant ruler and laid it across the North Fork canyon, on a right angle, from Moody Ridge, to, say, the accordant Giant Gap Ridge, across the canyon to the southeast, one would find that that ruler was about dead level.
One can actually fit a plane to these accordant ridges, and thus restore implicitly the surface of the Pliocene andesitic mudflow plateau. I have done experiments with such plane-fittings using software which allows me to create virtual landscapes, based upon USGS Digital Elevation Model data, for this area--very very accurate models in which elevations are known on a square grid of 30-meter intervals. The software requires me to express the planes I use for fitting in terms of their surface normals and distance form the origin. It is a little cumbersome.
The Pliocene plateau sat atop the Sierran slab, and when the slab tilted up, the plateau tilted with it. There appears to have been about 4000' or 5000' of uplift at the Sierra crest near Donner Pass. It occurred over a few millions of years, and is still occurring. We shall have earthquakes which will thrown down many or all our old brick and stone buildings, in towns like Dutch Flat, Colfax, Grass Valley, and Nevada City.
So, the whole slab is tilted up like a trap door, sloping gently down to the southwest, and a system of "consequent" streams developed on the plateau; geomorphologists might say that the streams (the Feather, Yuba, Bear, American, etc.) are "consequent upon" the gently sloping surface. In other words, they incised their courses directly downhill, to the southwest.
Then came the Pleistocene, less than three million years ago, and glaciation seems to have spurred rapid incision of the canyons, so that they cut through the andesitic mudflow, cut through the rhyolite ash beneath it, cut through whatever river gravels etc. which may have been underneath that rhyolite ash, and then hit the bedrock, and just kept right on cutting, down and down and down.
So that, for instance, right here at the northeast end of Moody Ridge, the North Fork canyon began by cutting through 250 feet of mudflow (4200' to 3950'), then 50 feet of rhyolite ash (3950' to 3900'), then 2,100 feet of the Mesozoic serpentine of the Melones Fault Zone (3900' to 1800').
And all this happened within, let us imagine, the last four million years.
So with simple arithmetic we can express the *average* rate of incision, in, say, inches per thousand years, or small fractions of an inch, per year (nowadays geologists like to express incision in terms of millimeters/year; I like inches per thousand years, myself). We say, the canyon has incised itself 2,400 feet in 4 million years, and find the average rate to have been, then, 7.2 inches per thousand years, or .72 inches in a hundred years.
This is quite a rapid rate of incision. My own instinct is that it is slower than that, right now, and that it accelerates during glacial maxima, of which maxima there have been many, over the past few million years.
Now, the sources of the andesitic mudflows which had built up the plateau, over millions of years time, were volcanos near, or on, the present Sierra crest; so it is natural, and correct, to surmise that these mudflows are thicker near the crest, and that they thin as one gets farther and farther away from the crest.
A geologic map of this whole part of the Sierra confirms that surmise; if one focuses upon the mudflows, which are typically given some kind of orange or tan color on the map, one sees as it were the many accordant ridges, with the dendritic branches of the canyons dividing one patch of mudflow, one ridge, from the next; and the patches are larger and much concentrated in the middle and upper elevations, but become scarcer and smaller down lower in the foothills.
Nevertheless, to this day one can find andesitic mudflows which reached the Sacramento Valley itself. One is exposed along Sierra College Boulevard, near Rocklin, south of I-80.
All the above is prologue, then, to a simple question: given that the northeast end of Moody Ridge is capped by 250 feet of andesitic mudflows, how many different mudflows can be identified within this section?
At higher elevations, where recent glaciation has exposed huge expanses of mudflow, one sometimes obtains quite a good look at multiple different layers of andesitic mudflow. These would probably obtain the status of distinct named "formations," if a precise geologic map were made.
Since I aim to make a precise map here, it behooved me to go out hiking and walking and thrashing through the brush and try to establish exactly how many different mudflows exist, right here.
I was surprised to find only two, or possibly four, different mudflows within this 250-foot section.
From the summit of the ridge, at about 4200', down to about 4100', there is one mudflow, characterized by very rotten boulders of light brown and yellowish and tan andesite, embedded in a matrix of very light-colored, grey and tan andesitic (?) ash.
This stratum, of about one hundred feet in thickness, is well-exposed in a certain roadcut. The rotten boulders were cut in a perfect plane; it is quite amazing and even pretty, in its way, to see all these thousands of spheroidal andesite boulders, in cross-section. I hesitate to even call this stuff andesite, for it is so deeply weathered and rotten now, despite being the highest and youngest mudflow locally, that it simply cannot be the same rock as the very sound and solid boulders of the lower, older strata.
As one drops lower in the upper, rotten mudflow, there begins to be an admixture of real, sound, andesite boulders. And as one nears the base of the stratum, there is a discrete layer containing many large andesite boulders, perfectly sound, and in freshly-broken chunks this rock is seen to be dark grey to black, with small white flecks of feldspar, such as one should see in a proper andesite. These boulders range up to four feet in diameter. There are occasional very small fluvial deposits, or so they seem, within this Stratum of Big Boulders. The Stratum of Big Boulders is only about ten feet thick. It seems to grade directly into the Stratum of Rotten Mudflow above it, yet I am tempted to separate the two into distinct formations.
Immediately below the Stratum of Big Boulders, and extending from about 4100' down to 4000', is the Stratum of Cement. This is a classic andesitic mudflow, identical in appearance to many exposures in the higher elevations, such as on the very summit of Castle Peak, near Donner Pass. Boulders and cobbles of sound andesite, up to a couple feet in diameter but commonly less than one foot in diameter, and sometimes well-rounded, but often quite angular and only slightly rounded off, and all these boulders and cobbles are embedded in a light grey matrix of andesitic ash.
In this Stratum of Cement (for this mudflow looks much like a rough concrete) one can find the remains of branches and limbs of trees, and fragments of leaves and conifer needles. Usually the wood rotted away to nearly nothing and left a hollow, a perfect mold, in the mudflow; but sometimes one can find the punky remains of wood millions of years old, within these hollows.
I speak of the Cement Stratum here on the northeast end of Moody Ridge; elsewhere, and more typically, the same formation, or its close relatives, will not display any fossil organic material whatsoever.
On the other hand, near Donner Summit I myself found a perfectly-preserved impression of a Madrone leaf, in just such a mudflow stratum, a stratum which contained a thin layer of finer sediments; and in these fine sediments are many leaf fossils, mainly, though, fir needles, by their appearance. The Madrone leaf was quite a lucky find. Geologist David Lawler saw that the fossil found a proper home, with the paleontology people at U.C. Berkeley.
Back to the northeast corner of Moody Ridge: below the ~100-foot thick Cement Stratum is a very poorly-exposed stratum which for all the world looks like something intermediate between the out-and-out andesitic mudflow above, and the out-and-out rhyolite ash strata, below: it is a light-grey stratum of volcanic ash, perhaps andesitic ash, perhaps grading towards rhyolite in chemical composition, and embedded in this ash stratum are just a few cobbles and small boulders of sound andesite. The stratum appears to be about twenty or thirty feet thick, maybe a little more.
So, naming this the Intermediate Stratum, I have tentatively identified four distinct mudflows or "formations" in the global andesitic mudflow "cap" at the northeast end of Moody Ridge. Listing them in descending order, youngest first and oldest last, we have, then,
1. Stratum of Rotten Mudflow.
(unconformity?)
2. Stratum of Big Boulders.
(unconformity)
3. Stratum of Cement.
(unconformity)
4. Stratum of Intermediate Composition.
(unconformity)
rhyolite ash, fluvial deposits, several to many unconformities
(unconformity)
bedrock
I write "unconformity" wherever there has clearly been a break in the deposition, that is, many thousands of years, perhaps even a million years or several millions of years, could fit into any one of these unconformities. During those time periods the uppermost stratum was an erosion surface.
Between the Rotten Stratum and the Big Boulders Stratum I am not sure if an unconfomity exists. It could well be that the Stratum of Big Boulders is derived from, say, a few million years of erosion of the underlying Stratum of Cement. This erosion freed big boulders from their matrix as the fines washed away, and thus slowly concentrated these very slowly-eroding boulders at the surface. Then, as I imagine it, the Rotten Mudflow roared over the erosion surface of the Cement Stratum, and very likely swept up and entrained into its own messy mass many of these boulders. Being dense and heavy, they tended to remain at the bottom of the flow. Hence they remained concentrated, and hence the Stratum of Big Boulders.
Beneath the andesitic mudflows are various strata of rhyolite ash, in this area interbedded with volcano-fluvial deposits, since the Eocene-age Nary Red Channel is quite close by on the northeast. This ancient prevolcanic river channel, akin to those in Dutch Flat and Gold Run, was apparently never entirely blocked up by the rhyolite ash eruptions of the Oligocene and early Miocene, so the river continued to flow, but the erosion surfaces upstream were fairly well covered in volcanics, so most of the cobbles and sediments in the upper strata of the channel are of rhyolite.
However, the andesitic mudflows subsequently filled up the Nary Red Channel valley to overflowing, and that was that.
Well, I haven't been writing much lately, but I have been at least thinking about the North Fork, and its geology, and its trails, and so on. I have studied the geology of the Sierra for about forty years now. So far as my understanding of purely local geology goes, I find myself collating results as it were, re-examining my own observations and my readings and drawing new conclusions, of which I hope to wrote more in the future. For instance, I am about certain that in older glaciations, such as the Tahoe I and Tahoe II, of 130,000 and 65,000 years ago, ice came down Canyon Creek and broke through the divide just northeast of Moody Ridge, directly over the axis of the ancient Nary Red Channel (no coincidence, the dividing ridge was weaker there), and hung down the canyon wall at least a little ways towards Green Valley, all the while quarrying out the gigantic chunks of rhyolite ash which one finds, today, away down on the floor of Green Valley itself.
This patch of rhyolite mega-boulders is drastically out of place and will definitely appear on my precise map of Green Valley. It is one of the more interesting formations down there.
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