San Andres Fault - Bay Area
This image shows San Andreas Lake and Crystal Springs reservoir from the air, looking SouthEast The highway paralleling the lakes to the left is Interstate 280, ``the most beautiful urban highway in the United States''. (And it is indeed very scenic.)
This valley is remarkably straight because the San Andreas fault runs down its center. The San Andreas is a classic ``Strike Slip'' fault: the two sides (for the most part) move past each other horizontally. (San Francisco Bay is there at least partly because the block between the San Andreas on the West and the Hayward fault on the East has been downdropped a bit, but that motion is small compared to the tremendous horizontal displacements that have occurred along these faults.) The vegetation and terrain on either side of the lakes look different partly because the underlying rock IS geologically very different. The rock on the right came from the Southern Sierra Nevada mountains, and has been transported from several hundred miles to the South by motion along the fault. With each San Andreas earthquake, it continues a few more feet (or tens of feet) on its long slow journey North (eventually to be plastered onto Alaska?). Source = The San Andreas fault and the Bay Area
Other sources:
The San Andreas Fault - Contents
San Francisco Earthquake of 1906
Regular MPEG movies - Pasadena