Extent of Glaciation

The Sierra Nevada has undergone repeated periods of glaciation in the past 1.5 million year, and glaciers are responsible for carving many of the spectacular canyons in the Sierra, including Yosemite Valley.

The most extensive glaciation in the Sierra Nevada occurred during the "Sherwin" glaciation about 1 million years ago (this is what the map displays). However, several other glacial periods - as recent as 15,000 years ago - have occurred.

There are currently about 100 small glaciers in the Sierra Nevada, and several hundred smaller "glacierets".

See also:

Sources:
Atlas of California, 1979.
Glaciers of California, Guyton, 1998.