Talk:Geology of the Yosemite area

Can we generalize this to Geology of the Sierra Nevada, just as we generalized to Biology of the Sierra Nevada ? -- hike395 02:46, 13 Mar 2005 (UTC)


 * I plan to, but not by generalizing. I intend to add detail from sources I have about the geology of the other Sierra national parks and about the entire Sierra. Turns out that there really isn't that much more to add to make this happen but I do need to check to see exactly what parts are specific to Yosemite and label them so (as with anything that is specific to the other national parks, once I add that info). I plan to start this sometime soon after the main Yosemite article becomes featured (and likely after I create geography of the Yosemite area). BTW, many of the sources I've used so far have a lot of specific detail about Yosemite Valley that I have avoided putting here since I want to create a separate geology of Yosemite Valley article. --mav 04:20, 13 Mar 2005 (UTC)

Shaffer POV material
A large quantity of pro-Shaffer material was added by an anon editor. This can be made NPOV: I'll place the material here, so we can work on it collectively. hike395 05:13, 4 May 2007 (UTC)

"Note that the comments above indicate that a massive "Sherwin glaciation" is almost certainly responsible for the excavation of Yosemite Valley, being some 3000 feet thick in the Valley according to Matthes. Shaffer, pursuing this idea, says, if so, why is there not one single erratic composed of Cathedral Peak granite (unmistakable for its huge feldspar phenocrists) to be found anywhere on the north rim of Yosemite, starting at the top of Royal Arches, only 1,250 feet above the Valley floor, and extending upward?  Were the ice here 3000 feet thick there would have be hundreds of such erratics brought down by the Tenaya Glacier, which swept right down from Cathedral Peak, leaving such erratics as found near such locations as Olmsted Point above the Valley.  In fact, Shaffer now says, around Yosemite there appears to be but a single example that shows possible glaciation thicker, maybe by 500 feet or so, than the Tahoe:  a large stone identified as an erratic by Matthes which might as well be a landslide deposit from the slabs directly above which, Shaffer warns, is bound for a very large rockslide in the near future as shown by a long, deep separation crack on an exfoliation slab on the hillside above. None of the other evidence for pre Tahoe glacial deposits or effects exists, including those cited by Matthes and Wahrhaftig, and Shaffer knows, because he has walked to every one of these locations. How about pre Tahoe ice 700 feet thick at Glacier Point? The evidence, "erratics" near Sentinel Dome, does not exist. No ice ever passed over Glacier Point.

Shaffer (1997) provides further evidence which brings into question the timing of Sierra Nevada uplift, and therefore the conventional explanation for the formation of such Sierran valleys as Yosemite. A central tenet to all hypotheses involving the creation of westside canyons is the timing of the uplift of the range. Conventional view has the range attaining its present height within the last 5 or 10 million years, and attributes the deepening of canyons due to accelerated stream erosion, then glacial erosion, in late Cenozoic. But consider: the largest Sierran glacier originated on Mount Lyell and flowed some 55 miles downstream, reaching depths of almost a mile, and this glacial ice entered the whole canyon repeatedly, the clear evidence showing two such advances, the Tioga and Tahoe. At two places, in Tuolumne Meadows and near Rancheria Creek, Shaffer reports/has found extrusive volcanic rocks that far predate the glaciation at or near canyon bottom. The Meadows deposit, Little Devil's Postpile right next to the main Tuolumne River, indicates essentially zero excavation by those "highly-abrasive glaciers," as does a small but unequivocal deposit at Rancheria Creek, where the glacial ice was more than 3000 feet thick on at least two occasions. Similarly, a volcanic deposit, apparently extrusive but dismissed as intrusive with high improbability, can be found on the floor the Middle Fork Kings River Canyon above Simpson Meadow, where the local relief is 5000 feet. The field relations indicate that the repeated, large glaciers through this point could not have deepened the canyon by anything approaching the 400 m found by Stock (2003) for the South Fork Kings at lower elevation. (I've seen a sample of this deposit collected by Shaffer, and as a veteran of Garniss Curtis' KA lab at Berkeley, I will tell you, it certainly looks to me like the more competent rocks from the Bishop Tuff, but then I'm no petrologist.) As Shaffer (1997) shows definitively, the arguments made to support late Cenozoic uplift (pp 301 - 332) are mainly driven by theory that is known to be false in the Sierra. For example [see above] the Ransome/Huber approach depends upon being able to assume that stream gradients on the west side of the Sierra were more or less uniform from the foothills to the crest, when every streamcourse in the range shows the stepped topography cited as evidence for glaciation, including the never-glaciated Tule and South Kern River canyons. Without this assumption, the Ransome/Huber methodology to estimate uplift is inapplicable, and yet this is adduced by Huber as the main "field evidence" which supports late Cenozoic uplift. On the other hand, real field evidence shows without equivocation that, on the Feather River at least, the canyon must have had essentially its present depth (3000 feet) before the deposition of the Lovejoy basalt 20 million years ago. Why? Because the Lovejoy can be found on top, partway down, and right at the bottom, of this canyon. Moreover, recent gold mining near Lake Don Pedro has shown a relationship between the Table Mountain latite, the Mehrten volcanics, and the auriferous gravels that does not agree with the interpretation used by Ransome/Huber to conclude that the latite followed paleo stream valleys; rather, these appear to lie flat one on top of another, see Shaffer (1997) for a full description of these relationships with complete references. It must be pointed out that Shaffer has walked over essentially every glacial deposit on the Sierra westside, in part because of his work on Sierra trail guidebooks, and in part because of his interest. Nobody else, not Muir, not Matthes, not Huber, not Wahrhaftig, has walked over even a small part of this ground, so Shaffer is the definitive source on what the field evidence suggests about glaciation on the Sierra westside. The rejection of his ideas in the face of quite voluminous field evidence, his inability to publish in the refereed journals, speaks to a pervasive intolerance in this branch of science to radically new ideas. Shaffer (1997) and an additional recent, long addendum unpublished, ought to be studied carefully by those who are interested in understanding the uplift of the Sierra and the creation of that incomparable anomoly among valleys, Yosemite.

At this writing, May 2007, it appears probable that the basic form of Yosemite was initiated by a late Cretaceous detachment event of the shallow crust on the westside of the Sierra, with the Valley being the position of the largest and most prominent fracture of this detachment event, that is in essence, a graben rather as described by Whitney, long these many years the butt of jokes for such an absurd idea. But since Yosemite is by far the most cavernous Sierra excavation, since it achieves depths as great as any of the canyons excepting those on the Kings River in the Sierra, since the Merced is a small stream, and since now Shaffer has shown that the glaciers passing through Yosemite were quite modest compared to those on the Stanislaus, Tuolumne, and San Joaquin, how else will this extraordinary phenomenon be explained in terms of the conventional, or any other, ideas?"

These are additions to the article posted by User:69.239.149.185 and deleted by Hike395 and put here for discussion. The writing style is non-encyclopediac, in addition to the non-neutral POV. As to the current controversy, editors opinions don't really matter. If the information should be included in the article, additional sources confirming Shaffer's interpretations of the geology of Yosemite Valley should be added. KP Botany 20:36, 20 May 2007 (UTC)

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