Vast, polished granite walls rise from forests and lake shores, shaped by forces far older than the rock climbers who now trace routes across them. Standing beneath formations like Snowshed Wall at Donner Summit, where climbers begin inching their way up the stone as soon as the snow melts, it’s hard not to wonder: how did this landscape come to look like this?
If Truckee-Tahoe’s rocks could speak, they would tell a story stretching back millions of years.
According to the Lake Tahoe Basin Management Unit, around five million years ago, movement along major fault lines caused large blocks of the Earth’s crust to rise and fall, helping form the Sierra Nevada crest. In the area where Lake Tahoe sits today, two blocks lifted on the east and west while the land between them dropped, creating a deep valley.
At the time, the area was not yet a lake. Snowmelt flowed north through the valley, draining toward the Great Basin. About two million years ago, several large volcanic eruptions occurred. One of these — from Mount Pluto — sealed the basin’s northern outlet with lava and mudflows, allowing rain and snowmelt to gradually fill the valley and form Lake Tahoe…