How was Lake Tahoe and its basin formed?
The basin formed at least two million years before the lake. Many people think Tahoe was formed by giant glaciers; however glaciers came along too late to form the massive Tahoe Basin. Others have heard it was once a huge volcano. Volcanoes did not form the basin, but like glaciers, volcanic activity played a part in the formation of the Tahoe Basin. Around five million years ago a very active period of mountain building took place. Large blocks or plates were pushed up forming the crest of the Sierra Nevada. Where the basin is today, two parallel blocks pushed up, one on the west, another to the east. Between these, another smaller block slipped down. This created a very deep and steep sided valley basin, open to the north. The open north end allowed snowmelt to flow out of the basin, and then through valleys towards the east and down to the Great Basin. The “valley basin” changed into a “lake basin” some two million years ago when several large volcanic eruptions occurred. One of the
