Glaciers at the Gate

Geologic processes that created Yosemite Valley include glaciation, erosion, rockfalls, and earthquakes, and most of these processes are still at work shaping and reshaping the land. Ancient glaciers have left dramatic geologic evidence virtually everywhere in Yosemite Valley. Samples of most of Yosemite's sixteen types of granite were carried to this area by glaciers, and several of these granites are visible nearby where the road cuts through the terminal moraine, the mass of debris left behind after a glacier retreated. After millions of years of uplift and cutting by the Merced River, Yosemite Valley was 3,000 feet deep at the onset of the Ice Age. One or more glaciers filled the valley to its brim between 250,000 and 1,000,000 years ago, gouging it 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 that eventually filled with sediment and left today's level valley floor.

California · United States