Early ice advances during the Pleistocene nearly filled the valley because we find isolated boulders, or erratics, dropped by the ice on mountain tops high above the valley. The most recent advance, however, got down to the western end of the valley and stopped. The glaciers planed away the rock wall of the valley, probably triggering landslides that further eroded the valley walls. At its end, the glacier left a ridge of debris called a moraine, although it's difficult to distinguish the moraine itself from debris dropped later by rockfalls and avalanches. Further east, the high Sierra were completely covered in ice with only the highest summits exposed.
Created 25 November 2005, Last Update 21 December 2010
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