The USGS California Volcano Observatory

It's not just earthquake country!

by Margaret T Mangan, Scientist-in-Charge, USGS CalVO

• Volcanic Eruptions occur in the State about as frequently as the largest San Andreas Fault Zone earthquakes.
• California's "watch list" volcanoes are dispersed throughout the State and future eruptions are inevitable--the likelihood of renewed volcanism is on the order of 1 in a few hundred to one in a few thousand annually.