Mammoth Mountain is a lava dome complex west of the town of Mammoth Lakes, California in the Inyo National Forest of Madera County and Mono County. It is home to a large ski area on the Mono County side. Mammoth Mountain was formed in a series of eruptions that ended 57,000 years ago. However, Mammoth still produces hazardous volcanic gases that kill trees and caused ski patroller fatalities in 2006.