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A virtual climb up Gaylor Peak

Our Fall 1999 field studies culminated in a climb up Gaylor Peak, an 11,004 foot high peak just north of Tioga Pass at the east boundary of Yosemite National Park. Gaylor Peak is an excellent place to appreciate Sierra Nevada geology. The peak lies at the boundary of the Sierra Nevada batholith (Tuolumne Intrusive Suite) and the metamorphic rocks that existed prior to the intrusion of the granitic rocks. The metamorphic rocks include remnants of the Triassic Tioga Pass caldera (the site of a violent volcanic eruption roughly 220 million years ago), and a metaconglomerate (the conglomerate of Cooney Lake) that may have originated in a fluvial (river) environment (Schweickert and Lahren, 1993). The peak lies at the headwaters of the Tuolumne River and Lee Vining Creek, and offers spectacular views into the glaciated canyons that drain the crest.

Tioga Pass is a col, or U-shaped pass, that has provided access between the east and west sides of the Sierra Nevada for hundreds of years. A sharp glacial ridge perhaps once separated the two sides, but plucking of rocks by the glaciers flowing east and west from the pass eventually broke down the barrier. The glaciers abraded the rock, leaving behind tarns (in bedrock) and kettles (in glacial till and soil). The picture above shows Tioga Lake (foreground) and Ellery Lake at the headwaters of Lee Vining Creek. The Tioga Pass Road can be seen at the lower left. Ellery Lake is a reservoir used to produce hydroelectric power. The lighter rocks in the distance are the granitic rocks of the Sierra Nevada batholith, while the reddish brown rocks in the foreground are ancient metamorphic rocks of the Ordovician Palmetto Formation (roughly 450 million years old). Rocks similar to those seen here can be found across parts of western Nevada (Schweikert and Lahren, 1993).

Mt. Dana (13,057 feet) is the second highest peak in Yosemite National Park. It consists of several thousand of feet of volcanic breccia and tuff that collapsed into a caldera following a violent eruption about 220 million years ago. Glacier Canyon, visible on the left side of the peak, contains one of the remaining active glaciers of the Sierra Nevada, Dana Glacier. Although it was never very large in historic time, it was responsible for eroding the steep east (left) flank of Mt. Dana during the Pleistocene Ice Ages.  The glacier has lost more than three quarters of its area since 1908, and an even larger part of its volume, due to global warming in the last few decades (Huber, 1987).

South of Gaylor Ridge, one can see the valley of the Dana Fork of the Tuolumne River (this view is just to the left of the previous picture). Like Gaylor Ridge, the canyon lies at the boundary between the metamorphic rocks and granitic intrusions of the Sierra Nevada batholith.

The two lakes in this picture, Granite Lakes, lie in the cirque formed by glaciers flowing south and west (left) into the Tuolumne Meadows area. As ice moved away from the cliff, it plucked jointed and fractured rocks from the cliff face. This undercut the cliff, and more material fell onto the ice. The smooth slopes and peaks above the cirque were not glaciated, and essentially retain the original pre-glacial topography of the Sierra Crest. Click here for more information about the Sierra Nevada glaciations.

Looking west from Gaylor Peak ridge, we can see the Tuolumne Meadows area. With the exception of a few isolated peaks, everything in this picture once lay beneath a 2,000 thick ice sheet that flowed west (right) and south. The "domes" in the center left part of the picture (beyond the lake) are roche moutonnees which were plucked on one side to give an asymmetrical appearance. The dry depressions in the foreground are probably kettles, left behind as stagnant chunks of ice melted.

The intrepid climbers!

References:

Huber, N.K., 1987, The Geologic Story of Yosemite National Park, U.S. Geological Survey Bulletin 1595, 64 pages.

Schweickert, R.A. and Lahren, M.M., 1993, Tectonics of the east-central Sierra Nevada -- Saddlebag Lake and Northern Ritter Range pendants, in Crustal Evolution of the Great Basin and Sierra Nevada: Cordilleran / Rocky Mountain Section, Geological Society of America Guidebook, Dept. of Geological Sciences, University of Nevada, Reno, p. 313-351.

Pictures by Garry Hayes