Sierra Nevada Glacial Features

Allan James  (AJames@sc.edu)

Old Man Mountain (distant right) beyond Spaulding basin (foreground).  View is to the northeast toward the crest of the northwestern Sierra Nevada from Clyde Mountain.  Most of the area shown was glaciated during the Pleistocene.  Late glacial ice covered most of Old Man Mountain as late as 14,100 years B.P.; only a small peak protruded as a nunatak (James, 1994; James et al., in press).  

Old Man Mountain closeup.  Ten cosmogenic surface exposure dates have been determined along a transect up the right flank (James et al., in press).  There are very few numerical dates to constrain the late glacial maximum in the northwestern Sierra.  These dates suggest a relatively late rapid melting of ice from moderately high elevations during the last glacial maximum.

Devils Peak, a large crag-and-tail landform.  Ice flow was from middle left to upper right away from a deep valley glacier that flowed down the South Yuba river (from left to right). Ice flowed across an upland toward the deep gorge of the North Fork American River (beyond photo at right).  There has been some debate about the effectiveness of thin glacial ice as an erosive agent.  This streamlined landform is up on a plateau where ice was not much more than 100 meters thick.  The ice surface slope was steep, however, as the ice was flowing into a very deep canyon beyond (James, in review).

References Cited:

• James, L.A.  1994. Diversion of the upper Bear River: Glacial diffluence and Quaternary erosion, Sierra Nevada, California, Geomorphology 14(2): 131-148.
• James, A., Harbor, J., Fabel, D., Dahms, D. and Elmore, D.  (in press, expected May, 2002).  Late Pleistocene Glaciations in the Northwestern Sierra Nevada, California.  Quaternary Research.
• James, A. (in review).  Glacial Geomorphology in the Northwestern Sierra Nevada.  In, Butler, D., Malanson, G., and Walsh, S. (Eds.), Mountain Geomorphology, Proc. Binghamton Geomorphology Symposium, Oct., 2001.