Geology of the Lake Tahoe Basin

How Was Lake Tahoe Formed?

Although it is commonly believed that Lake Tahoe was formed by the collapse of a volcanic crater, the Basin was actually formed by the rise and fall of the landscape due to faulting.

About 24 million years ago the Sierra Nevada block was formed by tremendous uplifting.  Two principal faults evolved: the eastern margin created the Carson Range, while the Sierra Nevada developed on the western side.  From the "up thrown" fault blocks, the highest peaks in the region originated while the "down thrown" block sank creating a large valley.

Lava flowing from Mt. Pluto on the north shore, then formed a barrier or dam across the Basin's ancestral outlet, the Truckee River.  Water from snowfall and streams flow into the Basin, gradually creating a lake several hundred feet higher than the present lake.  Eventually a new outlet was eroded from the lava dam creating the present path of the Lower Truckee River.

Following the faulting and volcanic period of the Basin, an Ice Age developed.  Huge glaciers formed and moved down the V-shaped canyons on the western side of the lake.  These glaciers scoured away loose rock and reshaped the canyons into broad U-shaped valleys.  The rock and gravel left behind at the sides and end of these melting glaciers are called moraines.  As these glaciers melted away, they also left behind brilliant bays, jagged peaks, glacial polished ridges and crystal clear lakes.

 

How Large Is The Lake?

Lake Tahoe is the third deepest lake in North America and the tenth deepest in the world.  The lake is 22 miles in length and 12 miles wide with approximately 72 miles of shoreline. Its greatest measured depth is 1,645 feet.  The average depth of the lake is 1,000 feet.  Another amazing fact about Lake Tahoe is that the bottom of the lake, 4,580 feet in elevation, is actually lower than the Carson Valley floor in Nevada.

 

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