Monday, October 18, 2004

Visit to Green Valley

Saturday morning I set off down the Green Valley Trail near Alta. The canyon was full of smoke from the recent fires, and the sun seemed sickly and cold. Some friends, including Steve Hunter and Jerry Rein, were camping at the Old Hotel site. I imagined a leisurely cup of coffee with them, before they began their fly fishing, and I would cross the river to take a look around the Hayden Hill Mine.

Green Valley is an exceptionally wide part of the North Fork canyon, just upstream from exceptionally narrow Giant Gap. I have often written of this contrast, which reflects the weakness of the serpentine of the Melones Fault Zone (Green Valley), and the massive durability of metavolcanic rocks of the Calaveras Complex (Giant Gap). Green Valley is like a broad amphitheater, Giant Gap, a narrow gorge.

In Green Valley are many deposits of "glacial outwash," bouldery sediments from the North Fork glacier, upstream. The outwash bears gold and was mined every which way a century and more past.

Rivers and streams carry sediment. From an abstract standpoint, imagine a long wooden trough, V-shaped, sloping gently from one end to the other. Let the trough carry a fixed amount of water, from the upper end to the lower end, where it spills freely away. Now steadily pour a small amount of sand into the upper end, such that the water in the trough carries it away. Very well. Increase the amount of sand. At some point, as the amount of sand added is increased, while the amount of water and the gentle slope of the trough remain fixed, some of the sand will start to "stick" in the trough. As more and more sand is added, a kind of narrow flood-plain will form in the bottom of the trough. The sediment load has exceeded the ability of the fixed amount of water to transport it.

However, if the supply of sand is cut off, while the water continues to flow as before, it will strip away the sand flood-plain, cutting the sand back down to the bottom of the trough.

This is essentially what happened, on the grand scale, in the Sierra. The glaciers in the upper reaches of our canyons drastically increased the sediment load delivered to the rivers downstream. Narrow, canyon-trapped floodplains developed. Then the glaciers melted away, sediment load returned to "normal," and the rivers cut through these outwash deposits, back down to bedrock.

When such an outwash plain forms in a narrow gorge, often little if anything is left for us to see, after the river has cut back down to bedrock. Such is the case in Giant Gap. But when the canyon is wider, vestiges of the outwash plain survive. The 49ers called such vestiges "bars," as, for instance, Pickering Bar, Euchre Bar, Humbug Bar, Fords Bar. Often some part of the original, roughly flat top of the outwash plain survives intact. Geologists call these "outwash terraces."

Only the most extreme flood events touch these vestiges, these bars, these outwash terraces, nowadays. It is interesting that the January 1997 flood event managed to nick most all of them, leaving fresh cross-sections exposed, where the layers of boulders and fine sediments can be observed directly.

And when the canyon is exceptionally wide, many vestiges of the outwash plain will survive. Such is the case in Green Valley.

There have been multiple episodes of glaciation within the past million years or so. The most recent ended only about 12,000 years ago. The geologists call this the "Tioga" glaciation, in the Sierra. Before the Tioga there were the "Tahoe" episodes, at roughly 65,000 and 130,000 years. Quite notable, too, was the Sherwin glaciation, about 750,000 years ago. Then there was the McGee Creek, at 1.3 million years; and near Mammoth, on the Sierra crest, there is a body of glacial "till" beneath a lava flow dated to 2.9 million years.

Now, one glaciation can do a good job of erasing the signs of another, older glaciation. Hence the record is fragmentary and challenging to interpret. It so happens that the Tioga glaciation was slightly less extensive than the earlier Tahoe glaciations, hence the Tioga could not erase all Tahoe deposits. The east side of the Sierra, where a much drier climate obtains, has many well-preserved glacial moraines of both Tioga and Tahoe ages.

The west side has relatively few well-preserved moraines, and much much more vegetation covering the landscape. The steep-walled canyons are not well-suited to preserving outwash terraces. Green Valley is an exception. It seems a certainty that outwash of Tioga, Tahoe, and even Sherwin glaciations is preserved. I would like to see a major study undertaken, of these glacial deposits in Green Valley.

The highest, and presumably oldest, outwash terrace in Green Valley is at the Hayden Hill Mine, on the south side of the river. The terrace top is fully 600 feet above the North Fork. A relict channel beside the Hayden terrace has a bedrock floor about 400 feet above the North Fork. I aimed to visit the Hayden terrace on Saturday.

So I dropped down the trail, losing 2100' of elevation, took the East Trail, passed Joe Steiner's grave, and met the Hunter party at the Hotel site. They were just on the point of leaving for a visit to Giant Gap, a mile west, so there was no coffee, but we stood around and chatted for a while. Steve has been exploring our canyons since he was a boy in the early 1950s. He knows them like few if any others. I told them I aimed to find a trail coming off the Hayden terrace, which I had walked in 1978, finishing that hike at a dead run, chased by yellowjackets, and figuring myself safe at the river, had been stung violently on an extremely tender part of my anatomy. A hornet trapped inside one's shorts is not a nice thing.

So they went west and I went south, crossing the river. The dimness of the day had kept the boulders wet at the one almost easy crossing point, so I took off my shoes and waded the cold river. I was surprised by thigh-deep water; water never looks as deep as it really is.

Across from the Hotel site is a line of low cliffs, with a gravel bar at their base. Atop these cliffs some large rounded boulders are perched, in the six-foot-diameter range. These are far too large to be transported by water alone, but, within a slurry of glacial outwash, they weigh much less. I scouted along, looking for my 1978 trail, and found it at the east end of the bar. It doesn't look like a trail at all, except by comparison with the cliffs near it. Ascending, I reached a terrace area about 60 to 100 feet above the river. Game trails and old human trails crisscrossed the area, and scouting east, I found a human trail crossing a deep "sluice cut" in the serpentine bedrock. I was almost directly across the river from the drain tunnel in the low cliffs a couple hundred yards east of the Hotel, which served the Green Valley Blue Gravel Mine. They were mining relict channels of the North Fork, set well back from the river.

I found an old, possibly Depression-era claim marker, a hand-hewn six-by-six set into a mound of boulders, beside the sluice cut. The cut undoubtedly dates from at least as far back as the 1870s. It was about ten feet across and twenty feet deep, blasted out of solid rock. Above it was one obviously mined-out basin, scarcely a hundred feet across.

At the base of the outwash terrace sediments is the serpentine bedrock. Mining always involved an effort, in such situations, to wash down to, and "clean," the bedrock. One would sluice off the terrace gravels, perhaps using a four-inch canvas hose and iron nozzle, and then carefully dig every last shred of loose material from the bedrock beneath, prying the rocks apart to get into crevices, where nuggets would be trapped. The coarse gold was always concentrated on the bedrock beneath the terrace sediments.

Crossing the sluice cut on a faint trail, I followed it east until it merged with a broad trail dropping back to river level, to a point a little upstream from White Boulders, where a few huge white boulders of some siliceous rock are scattered in the river, beside a large outcrop of the same material. This is some kind of exotic rock trapped right in the middle of the Melones Fault Zone serpentine. Boulders from this one outcrop are scattered down the river almost all the way to Giant Gap. I lopped along a little ways, but my aim was high not low, so I retreated and looked for the continuation of the broad trail, west and higher. I found it easily enough, but it split into multiple lines, and I chose the steepest.

Soon I saw trash, then, an almost brand new, tan-colored five-gallon propane bottle. I have learned that such propane bottles are a fixture of Mexican marijuana growers' camps. Knowing nothing good lay ahead, I continued up into a maelstrom of garbage, plastic tortilla bags and empty cans of hot sauce, another propane bottle and a Coleman stove, and no fewer than six sleeping bags. A pair of pants was draped across a tree, with some socks. A jumble of plastic sheeting, clothes, food wrappers, etc. etc. Pine needles covered parts of the many sleeping bags, suggesting an occupation date of summer 2002 or summer 2003.

The growers had hacked little trails into the hillside, some of which seemed to coincide with old-time miners trails. Occasionally a path would break out east to the edge of a large ragged serpentine cliff rising 400 feet or so from the river. I had great views east to the East Knoll of Green Valley, where a flume line was blasted into cliffs, and to Sawtooth Ridge, etc. Around 400 feet above the river, an old miners trail led out across the steep ground above the cliffs, and I followed it, lopping. The very east edge of the north-south running serpentine belt crossing Green Valley is the main trace of the Melones Fault itself; rock to the east is at first a melange of metasediments with some limy sediments and even marble, but quickly goes to another north-south faulted contact with the (metasedimentary) Shoo Fly Complex, running many miles up the canyon to the east.

I was looking across a narrow ravine cut into the ragged cliffs to the fault zone itself, where the vegetation abruptly changes. Many plants do not tolerate serpentine soils well, notably Ponderosa Pine and Kellogg's Black Oak. A sharp boundary is presented at the fault, with a Black Oak grove above to the east, and a naked cliff of serpentine dotted with Digger Pine and Canyon Live Oak to the west.

As the trail entered the ravine, it dropped and became indistinct. A deer or two had used it recently, I merely followed them. The human trail reappeared as the ravine was finally met, just below the main drain tunnel of the Hayden Hill Mine.

The tunnel, about six feet square, was mostly blocked by a cave-in at the entrance. Some White Alders and Pacific Dogwoods and Douglas Fir grew in the vicinity of the trail crossing, suggesting nearly year-around water at the surface.

East of the ravine the trail climbed steep slopes where it often disappeared altogether. I was having my doubts that this was any kind of old human trail, when I reached a sharp crest of serpentine within feet of the fault zone. An out-an-out cliff was descended by the trail, down an easy gully, after which the trail then continued nearly level and well-defined, into the more luxuriant forest east of the fault.

This high old trail is not shown on the modern USGS 7.5 minute Dutch Flat quadrangle. Another trail, which does not exist, is shown running roughly parallel, but down at river level, not 350-400 feet above.

When my high trail started dropping, I retreated to the ravine and the drain tunnel, which I had visited a few times over the past thirty years. Above lay the hidden valley of the Hayden Hill Mine, where hydraulic mining methods were used on the deep terrace deposits within and flanking a relict channel of the North Fork. This mine was active in the 1870s at least, perhaps earlier and later. There is a persistent rumor, which I have never been able to verify, that some kind of large slide buried "twenty" Chinese miners, and their sluice box, "way back when."

I decided to climb right to the top of the knoll to the west, a nice outwash terrace with acres of Black Oak forest enjoying the non-serpentine soils on its flat top. I passed two sluice cuts, each dumping into the ravine, each heading into small mined-out basins on the edge of the oak forest. Some grand old manzanita bushes grew near these sluice cuts. A miners trail was then struck leading up to the top of the knoll, 600 feet above the river. This is marked "Snakehead Point" on the Dutch Flat quadrangle.

There I stopped to take photographs. There is a nice view looking west through Giant Gap to Big West Spur and Bogus Spur, west of Lovers Leap. The Pinnacles were mostly all hidden behind the main spur of Giant Gap Ridge. To the east, some of the high red mining scars visible from Lovers Leap and Casa Loma were in plain view, showing stratified layers of glacial outwash not less than 700 feet above river level.

It may well be that these high outwash deposits are quite old, even Sherwin in age, 750,000 years.

The cellar of a long-vanished house is nestled among the oaks atop the knoll, with a fine view west into Giant Gap. There are some huge oaks atop that knoll. Hundreds of small Ponderosa Pine and Douglas Fir grow beneath the tall oaks. A cool wildfire would set things right, killing these small conifers.

Steep hydraulic banks face south and east into the hidden valley.

I dropped off the ridge on the southwest corner, down an old road of sorts, with some interesting mining equipment scattered along the way, including a massive trolley, perhaps for moving boulders. In a short distance the more northerly of two huge high tailings piles is met, a stack of boulders 200 feet high. It was interesting how many granite boulders were in the mix. These are common in the more recent outwash in Green Valley, and come from much higher in the canyon, perhaps the Loch Leven Lakes area, or Palisade Creek. They look quite sound and unweathered.

Could they be younger than Sherwin, so sound and unweathered?

I boulder-hopped down the steep pile quite cautiously; many boulders weighing in the hundreds of pounds rock back and forth on this dangerous mass. At the base I was not far from a stream, gurgling along, which heads up in the Black Oak forest above the fault zone to the southeast. A broad ditch left the stream to the north, and, following it, I remembered walking it in years past. It was once a well-used human trail, now heavily used by game. I lopped along, noting that I was some 200 feet above the river, in a fine grove of Ponderosa Pine growing in outwash-derived soils. Nearing the river, and the ridge-line of the marijuana growers' camp, the ditch ended, roughly directly above the deep sluice cut across from White Boulders. I followed game trails down to the lowest terrace, and then picked my way down the cliff trail to the river itself.

The smoke had slowly thinned and a brighter light and a stronger warmth suffused the canyon. The rocks at the almost easy crossing were dry, and I hopped across. No one was at the Hunter camp at the Hotel site. I rested for half an hour, and then made the slow sweaty slog up the Green Valley Trail.

It had been a fine day in the great old canyon, marred by the discovery of yet another horrible garbage site in Green Valley. It would take many backpack loads to haul this one site's garbage up and out. Maybe we should gather it all to the Hotel site, and get a TNF helicopter in there.

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