Morning: [...] Work on the trail; it is to the point where I can drive down to the parking area above the steps, but the dirt is dry, and I think I should wait for the rain to settle it before beginning compaction.”
[Russell Towle's journal]
“9/17/86 to bed early, now awake early to more gray skies, cool weather, and a nice fire burning in the stove, the last of my firewood, burning up as I write. Hmmm.
My sniffles persist. My head seems to be a clogged, congealed concretion of Romans, polyhedra, geology, square roots, Indians, music. I need to tend my garden.
A large hawk stopped by this morning in the top of the Cliff Fir. The Cliff Fir is a Douglas fir growing atop the cliff below my cabin; it appears to be fairly old, of moderate size, and somewhat storm-beaten since it is in a very exposed situation. It has an old-growth style of branching. The dark Hawk—perhaps even eagle—perched there for a few minutes, then soared away.”
[Russell Towle's journal]
“9/17/87 Afternoon; just returned from Lovers Leap where I spent a nice couple of hours with Dean Swickard and various other BLM personnel, plus a few odds and ends: Matt Bailey, a man named John from the Audubon society, and others whose names I don't recall; William McGinnis, from Whitewater Voyages/River Exploration Ltd.,” whose firm does the run through Giant Gap.
The agenda was mixed: discussion of rafting, commercial rafting, on the North Fork, and, Geri Landon was there; and there was some discussion of the upcoming TNF plan, and visual quality, etc. etc.; all in all, a very pleasant meeting. A charming young lady from BLM, Sarah, gave a little talk on the Big Oak (where we stopped for lunch), somehow tying it into the Constitution, today being the 200th anniversary of the latter.
Bizarrely [name] and a friend of his showed up while we were out there; and when I drove home, one of my tires went flat, which I may seriously question whether it was merely a matter of pure chance. I drove it home, flat, in shreds, an odd thing to do, it wasn't much of a tire anyway.
Later: just after sunset; it was definitely sabotaged; for, as I found upon walking up to the Meadow, both of the tires on the right-hand side were flat. They must have been punctured by [name]. Cute. It just so happens that I have an extra tire, so with the spare, the car has wheels. Jacked them up and put them on. I ruined both tires by driving on them.
So. What should I do about my punctured tires? Nothing, I'd guess.”
[Russell Towle's journal]
Date: Tue, 17 Sep 2002 19:42:27 -0800
From: Russell Towle
Subject: More on Big Valley
[This follows up on the email of September 15, 2002, (Subject: Visit to Big Valley):Hi all,
Why are these upturned layers of ancient rocks in Big Valley interesting?
After all, the Sierra Nevada is full to bursting with ancient rocks turned up on edge.
The thing of it is, in all these old metamorphic rocks, we have the evidence of episodes of continental accretion. Continents drift one way, the ocean floor drifts another, let us say, and the continents being made of lighter rock, the oceanic plates tend to dive beneath the edges of the continents; and stuff gets scraped off against the continental margin, and the continents grow. They drift east, and the eastern margin grows by accretion of oceanic debris—sediments, slabs of basaltic ocean crust, coral atolls, whatever—they drift west, and the western margin grows. And so on.
Not that the record of such accretion is clear in detail. Certainly not here in the Sierra. But if one grapples with the facts, and tries to come to terms first, as is only proper, with the very broadest outlines of Sierran metamorphic rocks—then some of the largest patterns will emerge. One of these is the serpentine of the Melones Fault Zone, a long (~100 miles) narrow belt of, presumably, ocean floor. It is around 200 million years old. It strikes more or less north and thus is not quite parallel with the Sierra crest, which strike northwest. It crosses the North Fork American near Dutch Flat. Paired with this serpentine belt are the rocks immediately east of it, the Shoo Fly Complex, the oldest rocks of the Sierra. They are mainly metasediments. The Shoo Fly also strikes north, and is exposed over a long distance, from near Yosemite up into Plumas County.
Under no possible construction can the Melones Serpentine be considered the "basement" upon which the Shoo Fly was deposited; this serpentine is far too young.
The Shoo Fly represents a long long time of deposition, just offshore the western margin of North America, as it was 400 million years ago, or so, when the beach was somewhere about where Nevada is now. I should say that the model of continental accretion is very neat and simple when one imagines the ocean floor moving at right angles to the continent, and a succession of stuff being scraped off against, and welded to, that continent. However, what about lateral movement, such as we see on the San Andreas Fault today, with its inexorable one or two inches per year of right-lateral motion? It is extremely difficult to quantify the possible lateral component of motion which may have affected Sierran rocks before and during accretion. That is, the oceanic plate may have been diving, not directly, but tangentially, under North America. Or the rocks of North American may have themselves been subjected to lateral motions, like we see on the San Andreas today, while oceanic stuff was sliding beneath and being accreted.
So when we say, the beach was in Nevada, 400 million years ago, we drastically over-simplify. We actually do not know where "Nevada" was 400 million years ago. The amount of lateral motion may have been huge. It might have gone one way for 100 million years, and then gone the opposite direction for the next 100 million years. Or there may have been very little lateral motion.
Back to Big Valley. First, the Shoo Fly. It was intensely deformed and faulted before it was ever added to North America. Part of it must have been uplifted above sea level and eroded., and then it sank below sea level again. At any rate, younger sediments were deposited on this disrupted, faulted, folded, and partly uplifted and eroded Shoo Fly surface. The lowest, oldest of these now lie immediately east of the Shoo Fly: the Taylorsville Sequence, Paleozoic in age. This sequence includes the Sierra Buttes Formation, of which the mountain of that name, near the North Yuba, is largely composed. The contact between the base of the Taylorsvile Sequence and the top of the Shoo Fly is what geologists like to call a "profound unconformity." That is, the two rock-groups—Shoo Fly and —do not comprise a continuous series of sediments, layer upon layer. The Shoo Fly was distorted, folded, faulted, eroded, and then the Taylorsville was laid down.
This profound unconformity is well exposed in Big Valley, which cuts the unconformity at nearly a right angle.
Sitting atop the Taylorsville Sequence are some younger, Permian volcanics and volcaniclastic sediments, and then still another series of still-younger, Mesozoic rocks. These begin with a narrow band of limestone and conglomerates and grade into the one-mile-thick Sailor Canyon Formation. Finally, the Tuttle Lake Formation (much of Snow Mountain is this stuff) lies on top of the Sailor Canyon fm. I shouldn't say "finally" because the complete sequence of Mesozoic rocks is still not known or brought into context with the aforementioned formations, partly because the Sierra Nevada batholith has too completely erased these rocks, which are exposed, patchily, still farther east.
Now, the whole shebang—the serpentine of the Melones Fault Zone, the Shoo Fly, the Taylorsville, the Permian volcanics, the Triassic conglomerates, the Middle Jurassic Sailor Canyon and Tuttle Lake—was tilted up to almost right angles at one time. This was the famous "Nevadan Orogeny," which tilted up all the rocks older than about 145 million years, in the Sierra. Most of our granites and granodiorites are younger than this; they welled up into the tilted and metamorphosed rocks from below, after the Nevadan Orogeny.
An "orogeny" is a "mountain-building," and many of the mountain ranges on our planet show the same kind of faulting and folding and tilting-up-on-edge as we see here in the Sierra. Of course, continental drift is the culprit.
Anyway. It so happens that Big Valley is especially well-designed to reveal these upturned strata in cross-section. Everything between the Shoo Fly and the Sailor Canyon fm., inclusive, is seen there, in its stark glaciated cliffs.
Moreoever, some of these rocks—the Taylorsville Sequence—are taking their last bow, as it were, right here. These rocks are well-exposed over large areas farther north, but thin down and shrink to the south, and end altogether at the North Fork American. In Big Valley we see them on the very verge of disappearing.
It would be nice if one formation were bright blue, another, red, a third, yellow; then one could tell them apart easily. Instead, one of these formations can look so much like another that even the very geologist who mapped them is not always sure what is what. So it is not as easy and direct as one could wish to become acquainted with these rocks.
Reading everything I have been able to obtain about these rocks, the conjectures as to their times and modes of accretion, and so on, I can say that not only are these rocks sufficiently difficult in the field, they are also more than able to intimidate and confuse in the safety of one's home. If the darn geologists would just agree upon the age of this, the time of folding of that, the direction of displacement of such-and-such major ancient fault, well, that would be one thing.
But they do not agree; so, that is quite another thing.
Nevertheless, having always enjoyed geology, it has seemed only fitting to try to understand these mysterious upturned rocks. One of the places one can see them at their best is Big Valley.
A Maze of Gorges
[North Fork Trails blogpost, September 17, 2007:
Ron Gould and I headed up to Emigrant Gap, then a few miles south on Forest Road 19, to Sailor Point. We parked and set off walking down a gated logging road. We hoped to find a way down the ridge dividing Sailor Ravine from the North Fork of the North Fork American River (NFNFAR); for this particular ridge (call it Sailor Spur) stands like a knife-edge above the many waterfalls in that area, forming a narrow promontory wrapped tightly by the 4000' contour.
|Sailor Spur ridge, above the "Gorge of Many Gorges"|
Half a mile brought us to the noble old Bradley & Gardner Ditch, or Placer County Canal, which was huge, glorious, intact, and very walkable on the west side of the road, but disappeared into the oceanic brush of a Tahoe National Forest clearcut, on the east. We continued down the road, which became tightly hemmed and overhung by brush, mostly that species of Ceanothus we call Deerbrush. In another quarter-mile or so the road struck sharply east, and we dropped away south into the forest, following the ridge.
Despite our fears we had easy going, and as the ridge-crest narrowed, if brush occupied its summit, we just dropped over onto the northern (shady) side of things, where often as not we found that the local bears had had the same idea, and their ponderous footprints could be seen dotting the leafy forest floor. Canyon Live Oak was quite common, with occasional old Ponderosa pines, and a scattered understory of young Douglas Fir. A mass of manzanita, then, might briefly run us off the ridge crest, but we always returned, and over a long distance, a very well-defined bear trail led us directly down the oak-clad crest.
The ridge plunged a couple hundred feet, and then Ron led us across a low swale in the oak forest. He forged ahead, into the sunlight on the far side. Soon I heard exclamations, shouts, and was pleased to think we had Arrived.
But we had not quite Arrived. We had reached the summit of a little spur ridge flaring south from Sailor Spur; this little South Spur had its own knife-edge crest, which dropped very steeply to the river below. We could hear the hiss and roar of several waterfalls. Across the canyon of the NFNFAR, to the south, was the sister-ridge to Sailor Spur, a spectacular knife-edge of rock; since this ridge, dividing the NFNFAR from the East Fork of that river, is named Scott Hill a little ways above and to the east, let us call this drastic arc of cliffs, this sister-ridge, Scott Spur.
Between Sailor Spur and Scott Spur the NFNFAR drops steeply, waterfall after waterfall, pool after pool, in a torturous series of abrupt curves. In a way, the NFNFAR presents the strange chance of a river entering its own gorge from the side. That is, there is a deep canyon; it is the canyon of the NFNFAR; and at a certain point, several streams enter the canyon, from the north, the east, and the south. They are like the fingers of a hand, radiating from the palm: Fulda Canyon, Sailor Ravine, the NFNFAR, the East Fork, Burnett Canyon, and Wilmont Ravine.
|A gorge, of many, in the Gorge of Many Gorges|
So. All these words are only to say that the NFNFAR plunges, very steeply, along a very twisted course, into its own canyon. Into the Gorge of Many Gorges.
Soon our little South Spur enticed us into a scramble, looking for some rocky viewpoint, but, having found such a point, we then could see one of the pools and some small waterfalls. They looked so close!
Yet the cliffs below were so steep! I decided to scout farther down the knife-edge crest, and found a kind of steeply-pitching rock ramp which made for pretty easy going. Soon we were on the river itself.
|The "Rectangular Pool" on the North Fork of the North Fork of the American River (NFNFAR).|
|Another view of the Rectangular Pool|
By "huge" I mean, blocks of slate which may be fifty feet on a side. But I saw no such huge exotic blocks here, on the NFNFAR.
We explored up and down only a few yards from the Rectangular Pool, for sheer cliffs and waterfalls stopped us almost immediately. Then we climbed back to the summit of South Spur. We could see our Ultimate Goal, that last long-jutting Promontory of Sailor Spur, a couple hundred yards away.
Approaching, we had some trouble with fallen trees. Quite a population of fire-adapted Knobcone Pine lives, and dies, along the almost level crest of the Promontory. Fallen pines lie around like jackstraws. It thus became a bit of a fight to follow the ridge, but soon we were rewarded by amazing, amazing and spectacular views of pools and waterfalls, of gorge upon gorge, canyon upon canyon. We followed along to the very tip of the Promontory, and enjoyed a good break out there, admiring the view, taking photographs.
|Ron and Otis|
It was another great day, in the main tributary of the North Fork, the North Fork of the North Fork.