Basalt, Clear Lake Volcanic Field

These freshly excavated boulders along Spruce Grove Road are basalt, which is an iron and magnesium-rich rock that’s fairly uncommon in the Clear Lake Volcanic Field. Most basalts in the Clear Lake Volcanic Field have been deeply weathered since eruption, so finding freshly excavated blocks that have been buried and thus not so deeply weathered is exciting for the USGS team. USGS photo by Dawnika Blatter.