Friday, November 18, 2005

Visit to Green Valley

I've been working on various projects for several weeks and have had little time for hiking in the North Fork. Yesterday, tho, I joined Catherine O'Riley, Jerry Rein, and Alex Henderson for a visit to Green Valley, an old mining camp east of Dutch Flat (see the USGS 7.5 minute Dutch Flat quadrangle).

We would walk down the old mule trail, beaten deep into the ground by the pack trains coming from Illinoistown, ten miles west. Parking is on Moody Ridge road, near Alta.

The river flows west at 1800' elevation, while volcanic mudflow tablelands to the north and south stand at 4200', hence a canyon 2400 feet in depth. In one of the great curiosities and contrasts of local geomorphology, two of the most notable strips of Sierran bedrock are in faulted contact in Green Valley: the serpentine of the Melones Fault Zone, also called the Feather River Peridotite, to the east; and the massive metavolcanic part of the Calaveras Complex, to the west.

The strips are near a hundred miles long, but only a mile or ten wide.

So in a few steps one crosses from a weak, shattered, sheared rock--serpentine--to a dark, heavy, not at all slate-like, but metamorphic, something?--I always used to think of the rocks of Giant Gap as metabasalt; they are something iron-rich, dark, mafic; but really I've little idea of the true origin of these metamorphosed volcanic rocks. They may be a mixture of ocean-floor basalts, quasi-sedimentary layers of ocean-floor basaltic ash, with patches of underwater turbidity flows, mixing pebbles of lava and basaltic ash and whatnot into something like a mudflow.

Blurring our focus, the two notable strips run north and south. But the canyons of the Sierra run east and west. Hence many Sierran canyons cut these same strips. For instance, this same serpentine reappears in the South Yuba to the north, around the town of Washington.

But rocks, whether in big strips or terranes like these, or in foot-thick sedimentary cake-layers, as in, a stratum of sandstone, can vary along strike. Say one finds the edge of a bed of sandstone and follows it; and after walking along a ways, it changes from sandstone to shale. It has varied along strike.

Similarly these terranes, like the Melones serpentine and the Calaveras Complex, vary along strike.

It so happens that just where that weaker-than-usual rock, the Melones serpentine, is near its weakest, and most like serpentine, and least like peridotite, is also just where the metavolcanic part of the Calaveras Complex is at its strongest, at its most massive, with the widest possible spacing of major joints and fractures in the rock.

And this is at Green Valley. At the west end of Green Valley, to be precise, where the fault separating the "two notable strips" crosses canyon and river alike.

One fully expects a canyon to change form if it passes from weak rock into strong rock. To study such changes is the joy of the geomorphologist. The Great American Canyon, the American River Canyon, the North Fork of the American River canyon, changes very dramatically here, as it passes from Green Valley, into Giant Gap.

One goes from an exceptionally broad portion of the canyon (Green Valley) to an exceptionally narrow part of the canyon (Giant Gap).

Or rather, I should say, one *doesn't* go: Giant Gap is renowned for impassability. Cliffs drop directly into long deep pools, ruffled by the perpetual canyon winds. There is no walking along the river.

The canyon depth is the same: 2400 feet.

It is always a pleasure to visit Green Valley and marvel at the dark cliffs of Giant Gap, of Lovers Leap and The Pinnacles, to the west. Down and down and down through manzanita and Digger Pine until at last the great complex of Ice Age sediments is met and its associated great forest of Ponderosa Pine spans the valley.

Within this broad forest are meadows and springs and many mines and old cabin sites and even a grave, that of one Joe Steiner.

I have an old photo of Joe Steiner standing on the suspension bridge, just below where we almost but did not ford the river. He died in Green Valley in 1949. He was the caretaker of the mining claims of the Dunkhorst family, who had purchased the old Opel mines in the 1890s.

Thursday was warm and sunny, one of those miracles of California weather. Temperatures were in the seventies. We saw flowers in bloom, some purple daisy-like things I take to be Erigeron foliosus, Leafy Fleabane, and some Scarlet Columbines. Oh: we also saw a Common Monkeyflower.

And many mushrooms, thousands and thousands of mushrooms.

And butterflies, and gnats. No, it was a lovely warm and sunny day, but for all that Alex astounded us by jumping right into the river, at the deep pool near the west end of Green Valley!

Earlier, we had thought to ford the river and visit the Gold Ring Mine, on the south side. Near the old bridge site we took off shoes and pants and hesitantly approached the water, over big boulders slick with dew. The sun warmed the trail a few feet above and behind us, but we were in an abyss of damp and cold and shade.

I stepped in, about mid-calf deep, and probed ahead with one foot, over the rounded, foot-diameter boulders which made the river's bed. The rounded boulders were slick, and would have to be crossed very carefully. But time to consider this was not given. An excruciating pain was building in my very bones, where my feet and legs were underwater. Immediately it became intolerable, and I exclaimed I could not do it, and climbed out as quickly as I could.

And then Alex jumped in! Astounding!

Later we would climb past old mines and through sunny woods to one of the old mining ditches, and follow it nearly to the east end of Green Valley, in a very pleasant and winding hike of perhaps a mile or a mile-and-a-half, and then, the sun lowering, we took a chance on following a cross-country route downslope and back west, and hit the river again at White Rocks, just upstream from the Hotel Site.

Here a big gravel bar was in fully sun, and we rested for a time before beginning the long climb up and out.

Willows and cottonwoods were yellow and gold, the river, calm and clear and cold and slow; calm, so that all day I was admiring the reflections of things, of cliffs, or trees, or brash bunches of river grass, willows, boulders, or sky.

So, it was a nice Indian Summer day in Green Valley, a bit short, as the days at large are short this time of year, but quite pleasant.

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