Gulf of California Rift Zone Geothermal Region

The Gulf of California rift zone is a complex transition zone between the dextral (right-lateral) motion of the San Andreas transform fault system and the northwestward progressing spreading ridge complex of the Gulf of California segment of the Eastern Pacific Rise. The Gulf of California and its onshore extension, the Salton Trough (which includes Mexicali, Imperial, and Coachella Valleys), are located over a series of rifts in the Earth's crust which are filling with sediment from above, chiefly from the Colorado River, and magmatic material from below. The Cerro Prieto geothermal field in Mexico and the Brawley Seismic zone in the U.S. are located above two of these rifts, and young volcanoes in these locations are evidence of intrusion of magma from below.

The volcanics in this exploration region are less then 5-million year old and associated with northwest folding, block- and thrust- faulting. Dacite is the most common volcanic rock, with a composition that ranges from basalt to rhyolite. The volcanic activity appears to be related to extension associated with the San Andreas fault system. The most recent volcanic activity is dated to 10,000 years ago. The heat source for the Geysers geothermal field is provided by a silicic magama chamber. Clear Lake Volcanic Field, California^[1]
Assessment of Moderate- and High-Temperature Geothermal Resources of the United States^[2]