These photos start at the southern end of the San Andreas fault, near the shore of the Salton Sea. To the south is a small segment of crustal spreadinga genuine divergent plate margin just like those in the deep sea, but here it is deeply covered with sediment brought in by the Colorado River. Thermal activity here takes the form of small volcanoes, seep fields and geothermal power plants. At the other end of the spreading segment, the Imperial fault begins (just off the map) and crosses into Mexico. Explore these faults on the U.S. Geological Survey's index map.