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The Clear Lake volcanic field erupted in association with and within the San Andreas Fault Zone. Although the San Andreas fault is the hallmark fault associated with the transform tectonic boundary between the Pacific and North American plates, the “boundary” between plates is more accurately described by a zone of faulting than by a single fault.

Just as the Bartlett Springs and Maacama faults are the major bounding faults of the Clear Lake volcanic field, the Collayami (purple) and Maacama (green) faults bound the Geysers Geothermal Field.

CalVO geologist Seth Burgess looking across Clear Lake at Mount Konocti, a prominent volcanic dome complex within the Clear Lake volcanic field. Photo courtesy of Alexander Rubin.

Block diagram of a normal fault, where the footwall drops below the level of the headwall

Block diagram of a lateral (strike-slip) fault, where two blocks are moving sideways past each other without vertical motion. 

Block diagram of a reverse fault, where the headwall is being pushed above the level of the footwall