Scroll around and zoom in to find most of the known trailheads throughout Southern California. This map was originally started by Dave Walsh, but has since become a collaborative effort by many mountain bikers in the area to document all the riding areas around. Of course, being a user-contributed map, it may not be 100% accurate. So always do your homework before venturing off into any of these areas.
View SoCal MTB Trailhead in a larger map