How Many Volcanoes Are There in California?

The US state of California contains a total of 20 volcanoes. Many of the state's volcanoes have been inactive for long periods of time, although others exhibit evidence of recent volcanic activity. Some of California's highest volcanoes include Mount Shasta, Long Valley, Mammoth Mountain, Lassen, Golden Trout Creek, Mono Craters, Inyo Craters, Medicine Lake, Coso, and Tumble Buttes. The four volcanoes with the greatest elevations are highlighted below.

The Four Highest Volcanoes in California

Mount Shasta

Mount Shasta is a potentially active volcano located within the southern part of the Cascade Range in Siskiyou County. It is the highest volcano in California, with an elevation of 14,179 ft. The stratovolcano last erupted in 1786, is believed to have been observed by French explorer Lapérouse. Mount Shasta contains numerous glaciers, including the Whitney Glacier, Wintun Glacier, Bolam Glacier, and Hotlum Glacier. 

Long Valley

Long Valley is a caldera located in eastern California, adjacent to Mammoth Mountain. It is the second highest volcano in the state, with an elevation of 11,122 ft. Long Valley is believed to have been formed 760,000 years ago, after a supervolcanic eruption emptied a magma chamber. There is approximately 240 cubic miles of magma located underneath Long Valley, making it one of the world’s largest calderas, with a length of 20 mi, width of 11 mi, and a depth of 3,000 ft. The caldera's last volcanic activity occurred 50,000 years ago. Although the timeline is unclear, geologists believe that future volcanic eruptions at Long Valley Caldera are inevitable.

Mammoth Mountain

Mammoth Mountain is lava dome located in the Inyo National Forest, within both Mono County and Madera County. The volcano has an elevation of 11,053 ft, and last erupted approximately 57,000 years ago. However, in 1989, the volcano experienced seismic activity, gas emissions, and tree kills along the Long Valley Caldera. Additionally, in 2006, the mountain produced hazardous volcanic gases that killed trees and resulted in ski patroller fatalities. Thus, the mountain is a potentially active volcano. The portion of the volcano located in Mono County contains the Mammoth Mountain Ski Area. 

Lassen Peak

Lassen Peak is a lava dome volcano located in the Shasta Cascade region, within Lassen Volcanic National Park. The volcano has an elevation of 10,462 ft, and the lava dome has a volume of 0.6 cubic miles, which ranks as the largest lava dome in the world. The summit of Lassen Peak contains many craters, and the last eruption occured in May 1915, which makes it an active volcano.

Recent Volcanic Eruptions in California

Three volcanoes in California have been flagged as high volcanic activity threats: Mount Shasta, Lassen Peak, and Long Valley. Eruptions can cause significant damage and fatalities, but current technologies are able to more accurately predict when and where volcanic activity is likely to occur.