Wednesday, October 22, 2003

Big Valley Canyon

From a particular clifftop perch below the East Summit of Big Valley Bluff, one can see the remarkable gorge of the lower, southern reaches of Big Valley Creek, as it enters the tremendous depths--here, around 3500 feet--of the North Fork canyon. The bare rocky canyon walls rise thousands of feet, and an inner gorge is often incised within the main gorge. Here are many waterfalls, seldom if ever visited by humans.

On Monday Ron Gould and I drove up I-80, took the Yuba Gap exit, bore right at the first fork, passing an obscure petroglyph site along the line of the Donner Trail, beside a long wet meadow, and then took the left turn onto Forest Road 19. Lake Valley Reservoir was on our right as we slowly climbed eastward to another left on Forest Road 38, which leads in past Huysink Lake (named after outdoorsman Bernard Huysink of Dutch Flat) and the popular Salmon Lake Trail, on past the unmarked Big Granite Trail, and beyond to Pelham Flat and Sugar Pine Point. Just past the wet meadow of Pelham Flat, a road breaks away right and winds down into Big Valley.

The USGS 7.5 minute "Cisco Grove" and "Duncan Peak" topographic maps cover this area, but do not show the more recent logging roads, such as the above road into Big Valley.

The old Big Valley Trail used to cross the valley here, on an east-west line, from Mears Meadow, atop Monumental Ridge on the west, to Pelham Flat, atop the Sugar Pine Point ridge on the east. At Pelham Flat the Big Valley Trail met the Sugar Pine Point Trail. Both trails have been obliterated by logging within the past 30 years.

We wound down the narrow road, hemmed in by thick brush, over slopes of glacial till, and forests of Red Fir gradually changing into the White Fir, Incense Cedar, and both Lodgepole and Jeffrey Pine which dominate Big Valley itself. All along the way we saw golden Aspens, and then down near the creek, golden Cottonwoods trees. Fall is here.

Big Valley Creek heads at Huysink Lake and runs south some five miles to the North Fork. It is incised into a variety of different metamorphic rocks, including the Sailor Canyon Formation, in the upper reaches around Huysink Lake, and rocks of the Taylorsville Sequence etc. in its middle reaches, until finally it enters the metasandstones, slates and cherts of the Shoo Fly Complex, in the lower reaches.

Big Valley is named for a large, mostly forested flat in the middle area, with scattered meadows, and only one bedrock outcrop of note, a glaciated mass of Triassic conglomerate on the west side of the creek. Flat-lying, light-colored, clay-like glacial sediments exposed in the creek suggest that this large flat may be a silted-in glacial lake. Another model might be a large glacial outwash plain.

Unlike Little and Big Granite creeks, immediately to the east, also running south to the North Fork, and of equal lengths, Big Valley has not one shred of granite in its upper reaches. The metamorphic rocks, most resembling steeply-dipping slate, are far more easily cut by glaciers and streams alike; for the granite is more "massive," with widely-spaced joint planes, and tends more to being rounded and smoothed by glaciers, rather than quarried away wholesale.

To the north, the shallow upper canyon of the South Yuba could not hold its own due portion of ice, and over a long succession of glaciations, glaciers swept right over the divide, into the drastically deeper North Fork canyon. Here again we see the contrast between granite (Yuba) and metamorphic rocks (North Fork). A deep pass at Huysink Lake marks the path of especially large volumes of ice flowing south through Big Valley. Even in the last, "Tioga" glaciation, which ended around 12,000 years ago, the ice was deep enough to fill Big Valley to the brim and even cover the ridges to either side.

It has become an article of geomorphological faith that glaciers carve "U-shaped" valleys, while rivers carve "V-shaped" valleys. Big Valley seems very U-shaped in its middle reaches, around the large flat; but the actual bedrock profile of the valley there is buried beneath thick glacial sediments, so who can say what its "true" profile is? Yosemite Valley presents a similar case. It is often described as U-shaped, but the bedrock floor of Yosemite is lost beneath deep glacial sediments. In both cases the bedrock profile may be more V-shaped than we might like, were we trying to apply our articles of faith.

And in the lower reaches of Big Valley, one sees a plain old V-shaped canyon, a gorge, really, despite the fact that here, if anything, the glaciers were thicker and bore down more heavily upon the rock, than to the north and upstream. Similarly, the main North Fork canyon, as it passes Big Valley Bluff, is rather distinctly V-shaped, even though its valley glacier was at least three thousand feet deep at this point.

So at any rate Ron and I parked and first scouted west across the flat to a fossil site I have never been able to find, with brachiopods and crinoidal debris. Once again I managed to not-find the fossils, although Ron spotted some patterned, limy rock which had a large number of blurred, indistinct egg-shaped masses within it. Perhaps these were the fossils.

We broke away to the south, crossed the dry bed of the creek, and soon struck one of the larger meadows. This wet meadow was crossed by some amazing bear trails, beaten wide and deep into the lush grasses, and, following one of these, we came to a perfect bear wallow, a hole in the meadow some five feet long by three feet wide, brimming with water, and showing signs of having been used only that morning. Bear trails converged upon the wallow from all sides. We held a southerly course and soon passed from the main flat of Big Valley into the rocky open slopes of the gorge, marked as "Big Valley Canyon" on the topographic maps. Suddenly the creek held water, suddenly the bedrock was exposed everywhere.

We picked our way along mild cliffs and through brushy areas, while the canyon plunged ever more steeply. The day was warm and bright, the sky a deep clear blue. Forest and meadow had been replaced by cliffs and scattered Jeffrey Pines and Western Junipers. Nearly a mile south from Big Valley we hit the first major inner gorge. This gorge-within-a-gorge was in the hundreds of feet deep, and contained a series of pools and waterfalls. By my reckoning we were far enough south to be in the Sierra Buttes Formation, which has an upper and lower member, and it seemed we were at the contact between the two, for the thinner, more slaty strata of the upper member suddenly graded into an alternating series of more massive debris-flow breccias interleaved with slaty zones. All was as usual tipped right up on edge, and in this case, the upper member was to the north, the lower member to the south. These rocks are submarine volcanics and volcaniclastic rocks, Paleozoic in age, but much younger than the Shoo Fly, a little farther south. They are intermittently exposed from north of their namesake, the Sierra Buttes, south to at least Picayune Valley. They are part of what David Harwood of the USGS dubbed the "Taylorsville Sequence," which lies to the east of the Shoo Fly Complex in the Northern Sierra.

We picked our way down cliffs to some pools below a waterfall, with rather astounding and even frightening cliffs rising hundreds of a feet above us, frightening, because massive overhangs held thousands of tons poised in the air as it were, directly above us. Some very nice breccia was exposed along the creek, dark slaty angular raisins in a pudding of gray volcanic ash.

After a lunch break, we left our packs and dropped down the inner gorge. We were a little uncertain about the first little cliff. I should say that these canyons in the Northern Sierra, whether little or big, are dangerous places. I used to think of the High Sierra, with its peaks rising twelve, thirteen, fourteen thousand feet above sea level, and its monstrous cliffs, as the truly dangerous part of the Sierra. I have since come to realize that our local river canyons, here in the north, offer every bit as much danger. So we approached this little forty- or fifty-foot step in the gorge with all due caution.

Picking my way down the almost vertical rock face, I saw, but could scarcely believe I saw, bear poop on a ledge. I pointed it out to Ron and we had a bit of a laugh over the bowel-moving tensions of climbing sheer cliffs. Once again I am reminded of how very well these bears do in the most extreme terrain. Ron and I had seen bear sign all the way through Giant Gap earlier this year, on the high old discontinuous Giant Gap Survey trail.

We saw trout swarming in some of the pools, and were intrigued by signs that the bear or bears had waded all through these trout pools. Do they fish? Maybe.

Turning a corner in the gorge, we passed into a narrow band of igneous intrusive rock, a long thin body of fine-grained gabbro which strikes across the canyon. Here the creek had cut a fine broad avenue floored by solid rock, oh, thirty feet wide, and hundreds of feet long, a plane surface sloping south, and we walked along this steep mountain sidewalk until suddenly another waterfall was met, this one at least fifty feet high, and the cliffs beside it looked quite challenging. We had only just then passed from the thin gabbro body into the first fault-bounded slices of the Shoo Fly Complex, here, thin masses of the Duncan Chert.

We had great views south to the East Summit of Big Valley Bluff on the right, and to the low pass on the Foresthill Divide, across the main North Fork, where the Beacroft Trail heads up. We were not quite far enough south in Big Valley Canyon to look back north and see some rather remarkable cliffs and spires of the Duncan Chert I had noted the other day, and had hoped to visit; but the gorge below us to the south looked quite challenging, quite difficult, and to reach the next relatively level and passable reach of Big Valley Canyon would mean a circuitous passage over the cliffs to the left, and a descent of another couple hundred feet.

We decided we had come far enough. Another mile and a half of gorge lay between us and the North Fork, and that last bit looks rather drastically steep. I still doubt that anyone has ever followed the creek itself all the way down; it would require rappelling again and again and again, over the waterfalls.

On our way back up and out I got creative and tried to forge a new route, the result being that I found myself almost trapped within a patch of sunny, hot, impenetrable brush. I had to struggle uphill against the grain of the stubborn bushes. Every once in a while I saw places where bears had busted out a little opening, but these openings always closed down again, and it was back to acrobatics, huffing, puffing, sweating, cursing, and all the while Ron was strolling merrily along up the bouldery creek below me.

That hundred yards of brush sapped my strength. I was more or less ruined. However, we were not far from Big Valley itself, and a little higher we discovered remnants of yet another old trail, which is shown on a 1939 Tahoe National Forest map, and which ran down the length of Big Valley, to the beginning of the gorge. This old trail made for easy going, and soon we reached the truck. I was a wreck.

It was a very interesting day, in a very beautiful place. The land acquisition efforts by Tahoe National Forest in this area should be continued. In particular, the private lands at Pelham Flat; Section 7, within Big Valley itself; Section 17, which includes Sugar Pine Point; and other lands near the head of the Big Granite Trail, all ought to be purchased from the lumber companies, if possible.

This lovely part of the Placer County high country has been fairly heavily impacted by logging.

In particular, the old-growth Incense Cedar of Big Valley must have made an amazing forest. However, I believe the wild and scenic and recreational values are more than enough to justify further land acquisitions in this area.

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