From our friends at the US Geological Survey:
USGS is aware of a letter circulating on the Internet that uses our logo and warns of an impending sizable earthquake in Southern California. USGS had no part in this letter or any alleged alert. USGS does not predict earthquakes. USGS distributes reliable and timely scientific information on earthquakes and makes it all available to the public at earthquake.usgs.gov. The message of being prepared is always valuable.
For a really nifty REAL TIME earthquake map, check out this link: http://earthquake.usgs.gov/earthquakes/map/