Eruption Episode 2 rocks, Clear Lake Volcanic Field, California

Detailed Description
Eruption episode 2 rocks are higher in silica than those characterizing Episode 1, and instead of being primarily lava flows that filled existing valleys, Episode 2 rocks commonly erupted as volcanic domes. Cobb Mountain erupted during this episode, as did Boggs Mountain. This photo was taken during a relatively dry year at Boggs Lake Preserve, when small boulders of Episode 2 dacite are exposed along the lake bottom. USGS photo by Dawnika Blatter.
Sources/Usage
Public Domain.
USGS photo by Dawnika Blatter