Geologic processes that created Yosemite Valley include glaciation, erosion, rockfalls, and earthquakes. Most of these processes are still at work here, shaping and reshaping the land. Ancient glaciers have left dramatic geologic evidence virtually everywhere in Yosemite Valley.
Take it for Granite
Yosemite's awe-inspiring granite formation have made the park world famous. Samples of most of Yosemite's sixteen types of granite have been carried to this area by glaciers.
Several of Yosemite's granites are visible nearby where the road cuts through the "terminal moraine," the mass of debris left behind after the glacier retreated.
After millions of years of uplift and cutting by the Merced River, at the onset of the Ice Age Yosemite Valley was 3,000 feet deep.
One or more glaciers filled the Valley to its brim between 250,000 and 1,000,000 years ago. The Valley was gouged into a U-shaped trough. About 30,000 years ago, a thinner glacier advanced to today's "Gates of the Valley." When this glacier melted, its terminal moraine dammed the Valley, creating a shallow lake. This lake eventually filled with sediment, leaving today's level Valley floor.