Monday, December 12, 2005

Cloud-bow Over the North Fork

Sunday morning I met Catherine O'Riley and old skiing buddy Kelly Olrich for a visit to Giant Gap, via the spectacular and steep Canyon Creek Trail, and the spectacular yet level HOUT (High Old Upriver Trail; pronounced to rhyme with "shout"). The day had dawned cloudy, and at 8:30 a.m. we shivered a bit in the parking lot of the (I-80) Dutch Flat exit's Tesoro gas station, where volunteers were gathering to search for the body of Christie Wilson. We waited for other possible members of our own party to arrive, and when none did, set off trespassing across the Gold Run Diggings to the trailhead in Potato Ravine.

It is said that a good crop of potatoes was grown in the meadowy headwaters of Potato Ravine, in the year 1849 itself. Hence the name.

Just west of the Diggings rises Cold Springs Hill, which retains a patch of the "Tertiary volcanics" on its crest, roughly horizontal layers of rhyolite ash surmounted by more layers of andesitic mudflow.

Since it is all less than thirty million years old, geologists incline to call it juvenile. It is "young." Beneath these "young volcanics" lies the ancient bedrock. What strata this bedrock has, has been rotated to a near-vertical orientation, with the upturned layers striking north. So the layers of the old rock, below, are at right angles to the layers of the young volcanics, above.

This is called a "profound unconformity." The two sets of strata are entirely disjunct. Sometime in the Jurassic, probably, this ancient bedrock crashed into the west coast of North American, carried on a subducting oceanic plate, and this part of it was scraped off and welded onto the continental margin.

Deep underground. Miles deep. And the strata of the stuff on this oceanic plate were tipped up vertical in the process.

Let a hundred million years of uplift and erosion follow. The somewhat mashed rocks are at last exhumed. A mountain range rises, is eroded into low hills with broad meandering rivers flowing in flat-bottomed valleys.

Then the young volcanics come along and bury it all.

Then the whole Sierra, breaking free from terrain to the east on near-vertical faults, rises, like a trap-door with its hinges buried beneath the abysmally deep sediments of California's Central Valley--and is tilted up into a steeper slope down to the southwest, and here, around these parts, a brand new set of canyons is cut into a kind of hummocky plateau of young volcanics.

The new canyons are about four or five million years old. Basalt on the crest of Sawtooth Ridge has been dated to 3.82 million years. The North Fork canyon has downcut about 2500 feet in that time.

They are not that thick, the young volcanics. And they are not that strong. So it does not take all that long for the brand new rivers to cut down into the ancient bedrock underneath. At first, large remnants of the hummocky plateau of andesitic mudflow remain on the ridges between nascent canyons; on the "interfluves." But as the canyons deepen, they also widen, and these remnants shrink. Smaller. Smaller. Smaller.

Rivers try to cut down to their base level. The North Fork's base level is around 50 feet in elevation, near Sacramento. Hence, with an elevation of 1600' in Giant Gap, the North Fork is in a position to cut much deeper yet. Eventually, in the process sketched above, the canyons would deepen and widen until the patches of mudflow on the interfluves disappeared altogether, and it will then be the ancient bedrock, from river to ridgecrest.

But that is two or three million years from now, and this, this is now. And now, the uplands between canyons still wear vestiges of the andesitic plateau, of the "young volcanics."

We kept our warm clothes on as we strode down the tiny trail, so charming in its passage through that odd mix of Dogwood and Knobcone Pine and California Hazelnut of Potato Ravine, into the Canyon Live Oak and scattered Bay Laurel of Canyon Creek.

As is usual in this part of the Sierra, a widespread understory of shade-tolerant Douglas Fir is growing beneath this elfin oak forest, studded with gnarled giants which have struggled for centuries against blizzards in winter, and an inferno of dry heat in summer--and if no wildfires intervene, the Douglas Fir will win out in the end, with other shade-tolerant, but wildfire-intolerant species, coming to dominate.

A critical point is reached when the young Douglas Fir breach the canopy of the oaks. With full access to sunshine their foliage rapidly thickens and shades a larger and larger area, weakening and slowly killing the oak.

So here as elsewhere in the Sierra we see the principles of forest succession in action, and the old-time Ponderosa Pine-Kellogg's Black Oak forest association of the uplands, and its compeer Canyon Live Oak forest of the canyon walls--both the products of thousands of years of regular wildfires--are being engulfed in shade-tolerant conifers like Douglas Fir, White Fir, and Incense Cedar.

As we dropped lower and Canyon Creek broke into a series of waterfalls, an inner gorge developed and the trail is cut into nearly sheer cliffs. In many places blasting was required. I would not expect that this trail was made early, in the Gold Rush itself, but rather somewhat later, perhaps in the 1860s, when Canyon Creek carried most all the tailings of the Gold Run mines, and was itself fitted with sluice boxes, between the many waterfalls. Then a good trail would have been needed. Many men would have tended these giant sluice boxes, twenty-four hours a day.

We visited those California Milkmaids in bloom at The Terraces, one of the places the miners used to camp.

Around the 1900' contour we broke away east and after a short scramble reached the thread-like HOUT. The river--the North Fork--roared calmly a few hundred feet below.

The HOUT is but the echo of a dream to steal the North Fork and sell its water to San Francisco. A Giant Gap Canal would be the centerpiece of this ambitious project of the late 1890s, with four tunnels. The line was surveyed and an approximation of the grade was nicked into the canyon wall. If necessary, a ledge was blasted from a cliff, along this (roughly) 1900-foot contour. This very grade served as a trail so that the work of surveying and blasting could continue; apparently several men were at work, starting in Green Valley and working west into Giant Gap, and starting at Canyon Creek and working east.

What remains of their efforts is the HOUT. A tiny little thread, with many a dip and a bump, but almost level on average--the Giant Gap Canal would have had a slope of ten feet in one mile--the HOUT must then be like a contour line and follow every twist and turn of ravine and spur ridge.

And there are very very many ravines and spur ridges, large and small, as one walks the HOUT. So it is quite an intricate path.

There are many vistas of Giant Gap to the east, or to the west, a fine series of interlacing spur ridges goes blue into a distance of several miles, near Iowa Hill, as one look down the great canyon.

All was still cloudy and the cliff-burgeoning gorge had narrowed enough so, under winter sun conditions, the sun tracking low across the southern sky, a great shadow not only enveloped the south canyon wall, rising two thousand feet and more from river to canyon rim, but crossed the river and reached up nearly to the HOUT itself, on the north canyon wall.

So a pool of cold air, which has intensified during the night, can be slow to leave the depths of the canyon, with shadows embracing so much area.

On the HOUT, one skims along near the top of the invisible pool of cold air dwelling in the canyon depths. The ins and outs of the canyon rim, across the river to the south, mean that the HOUT is in sun or in shadow.

We saw more flowers in bloom; something of quite aromatic stems, with a small yellow flower; and many buckwheats which have long since finished their ordinary bloom, back in June, say, and have for some reason decided that, with shriveled leaves and brittle stems, they will now, in December, flower yet again--it is quite odd.

Or not. This December buckwheat bloom is much reduced from the summertime masses of tiny flowers. One small flower here, another, there, and over here, three of them at the tip of one thin stalk. The plants look quite dead until one sees the itsy-bitsy flowers. Catherine spotted them.

We reached Big West Spur and turned around onto the west-facing slopes near the Bear Bed, with fine views down to the river below. Two of the drastic 90-degree bends of the North Fork in Giant Gap were in view, and much of the river for a mile down towards Canyon Creek.

But still no sun and the warm clothes were on as we had lunch.

Later, on the way back out, the afternoon sun dropped below the cloud deck and a fine pure light flooded cliffs and pinnacles and for the first time those sharp deep wintry shadows formed, which so well pick out the details of this oddly-sculpted gorge.

A large moon rose over ruddy Eagle Puke Point, the highest of The Pinnacles across from Lovers Leap. Here golden eagles used to roost and regurgitate large pellets of fur and bone, much like owls do.

We took our time. I lagged behind, taking photographs. The scene was magnificent. The sun was near to setting as we neared the Canyon Creek Trail again, and the clouds had thinned to bright patches of cirrus and cirrocumulus, dappling against a deep blue sky. The sun just kissed the canyon rim to the west. Suddenly I realized that a cloud bow had formed, on a patch of cirrus directly above the sun, in the twelve o'clock position were one looking at a clock-face.

It was a smear of color across otherwise white and light grey clouds. Similar to the sun-dogs one sometimes sees at three and nine o'clock on the "ring around the sun," so common in high thin cirrus. In fact, the angular separation of the cloud bow from the sun--which is so crucial to establish, for if one does not know this angle, one cannot tell which of five or ten types of cloud-bow, this one might be--the angular separation seemed "not dissimilar" to the angular separation of the ring-around-the-sun.

At any rate it was quite pretty. People don't often see cloud bows. There was a time, when I was young, when I indulged myself in a kind of nature mysticism; I was always seeing cloud bows, then, and they always had to do with romance.

In my world.

I would be walking to Dutch Flat, my latest piece-of-junk car dead, all obsessed with this or that romance, this or that woman, upset, or in love, or heartbroken perhaps, muttering to myself, "Well, at least I haven't seen a cloud bow, with *her*! She's not like the others, then. No cloud bow, no stupidly thinking, 'She's the One'"--

And then, of course, I would see a cloud bow. Yet another cloud bow. I think of them as rare, but if one is attuned to cloud bows and looks for them, one will see them.

We slogged slowly up the steep trail and reached the truck well after sunset, around 5:15. There was plenty of light, tho, and the waxing moon, nearing the full now, was in close conjunction with what I took to be a planet, maybe Mars or Saturn. Some other planet blazed white to the west, likely Venus.

The moon was like to occult the planet (or star), but I guessed it would not, or much ado would have been made, on television.

It was another great day in the great canyon.

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