Lake Tahoe geography is what knits together the incredibly beautiful mountains, forests, rivers, and, of course, lakes of the basin and its surroundings. The history of Lake Tahoe began a short two to three million years ago with geologic block faulting. The earth thrust itself up along what are now referred to as the Carson and Sierra Nevada ranges, and down between them in what is called the Lake Tahoe Basin. Some of the highest mountains resulting from this upheaval are Monument Peak (10,067 ft) overlooking South Lake Tahoe and the location of the Heavenly Mountain Ski Resort, Mount Tallac (9,735 ft) which is a popular summer hiking destination, and the Desolation Wilderness' Pyramid Peak (9,983 ft).
During the last Ice Age, which began some 40 million years ago – long before that geologic block faulting – and which is ongoing, Lake Tahoe was further carved from the landscape by the movement of frozen water. The winter snows have been melting in the spring for perhaps 10,000 years and long ago filled the basin with water. The Lower Truckee River, which begins at Tahoe City on the West Shore of Lake Tahoe, winds its way through Truckee and Reno before emptying into Pyramid Lake, is the sole outlet for the lake's water. The Upper Truckee River, flows into the lake from Meiss Meadows. Four peaks act as the source of much of the river's initial volume: Stevens, Red Lake, Echo and Ralston peaks.
The climate of Lake Tahoe reflects its location nestled between the Sierra Nevada and Carson mountain ranges. Annual precipitation on the western slopes of the Sierra Nevada range averages 55 inches. On the eastern shore of the lake 26 inches is typical. For Lake Tahoe itself the average precipitation is 30 inches. That's an average of 216 inches of snowfall and 8.3 inches of rainfall. The mountains support between 350 and 600 inches of annual snowfall. Most precipitation falls on the lake and enough evaporation occurs daily to keep the water running in Los Angeles for an entire day as well. The lake itself is 22 miles long and 12 miles across and the shoreline is 72 miles around. Forests are mostly pine and fir trees, but mountain alders are found along many area streams.