Michael R. Forrest
Geologist, Southern California Earthquake Center, USC
Dr. Forrest is a regular contributor to the Los Angeles Times where this story first appeared on November 12, 1995.
The "Fault Activity Map of California and Adjacent Areas" looks like what might happen if you left a lovely glass etching of our state in the hands of a little boy with a hammer and lots of Twinkies. In red, green, brown, black, and violet, the 20-square-foot map shows normal faults and reverse faults and strike-slip faults, faults of unknown affinity, faults with oblique slip, faults onshore and off and, for good measure, faults in parts of Nevada and Oregon, as well as Baja.
All told, the map, published by the California Division of Mines and Geology, indicates thousands of faults, plus a few hundred volcanoes. The oldest faults are rendered in bold black lines; active faults - like the San Andreas and the San Jacinto - slash across the state in unnerving red swaths.
With the exception of Japan, no other region in the world has a fault map covering such a large area in such detail (and at $20 through any of the division's offices, it's also a bargain). "This pretty much represents what we know," says Charles W. Jennings, the retired senior geologist for the state's mines and geology division who authored the map.
An update and an elaboration of the fault map he produced in 1975, this version took Jennings and an assistant four years to complete. One reason: it was drafted entirely by hand.
If you want to find fault with California, the map is available from the California Division of Mines and Geology at 107 S. Broadway, Room 1065, Los Angeles 90012. The phone number there is 213-620-3560.
