Lake Tahoe formed 4-5 million years ago when two parallel fractures caused the basin to sink while surrounding mountains rose. Volcanic eruptions blocked the north side of the lake around 2-3 million years ago, raising the water level. The west side was covered by glacial ice. Common plants and animals in the area include the Large Leaf Lupine flower, black bears, and Jeffrey Pine trees. Rocks in the region include granodiorite, quartz, basalt, conglomerate, and diorite.