Desolation Wilderness Geology

[Photo]:  Granite ridgeline above Boomerang Lake in Desolation Wilderness.  2001 Amy L. Reid, USFS.

The granitic mountains of the Desolation are part of the massive Sierra batholith, the combined masses of granitic rock that have been uplifted by tectonic action to form the 400 mile long Sierra Nevada range. Extensive glaciation has shaped the surface of the Desolation Wilderness. Ice sheets over 1,000 feet deep covered the western slopes and all but the highest peaks of the Tahoe Basin during the last ice age over 200,000 years ago.

The sheer mass and grinding action of the ice packs scoured out the basins where Emerald Bay, Cascade Lake, Fallen Leaf Lake, Echo Lakes, and nearly 130 other smaller lakes formed throughout the Desolation area. When the glaciers receded 10,000 years ago, they left behind massive deposits of unconsolidated rock and sediment. Glacial features of special interest include glacial polish, erratics, and roche mountonnee. In the last 10,000 years, some areas have grown over with forests and meadows, but most of the Desolation clearly shows its icy heritage.