LAKE TAHOE

Recall from my "Tectonic Plates, Simply" page that the lithosphere is the rigid, outer layer of the Earth.

     In the Lake Tahoe region—as in much of the American West—the lithosphere has been stretching for millions of years. When it stretches, the brittle upper layer (the crust) cracks along faults, much like pizza dough might tear when pulled apart. These faults create blocks of crust that can uplift, sink, or tilt.

     The Lake Tahoe Basin began forming over two to three million years ago due to movement along two major faults in Earth’s crust. The crustal block between them tilted downward to the east. The eastern edge dropped, creating the steep shoreline we see today, while the western edge rose, forming the more gradual Sierra Nevada slope.

     Eventually, water from snowmelt, rainfall, and stream inflow filled this tectonic basin. Later, during the Ice Ages, glaciers advanced into the region and left behind piles of rock and debris called moraines—natural dams made of glacial sediment. These moraines helped block water outflow, deepening and shaping Lake Tahoe. Glacial activity also sculpted the surrounding terrain, carving U-shaped valleys and adding to the dramatic landscape.