Lava Beds National Monument in Northern California is home of the Medicine Lake Volcano which has erupted 9 times in the last 5200 years including, most recently, 890 years ago. The park protects multiple lava flow areas as well as over 700 lava caves, the largest concentration of lava tube caves in the continental United States.
Lava Beds National Monument – California
Lava Beds National Monument - Lava Caves – California