Mammoth Mountain is a lava dome complex in Mono County, California. It lies in the southwestern corner of the Long Valley Caldera and consists of about 12 rhyodacite and dacite overlapping domes. These domes formed in a long series of eruptions from 110,000 to 57,000 years ago, building a volcano that reaches in elevation. During this time, massive dacite eruptions occurred roughly every 5000 years. The volcano is still active with minor eruptions, the largest of which was a minor phreatic (steam) eruption 700 years ago.