The easiest way the get relatively accurate and complete information about easy-to-mild 4wheeling in the Southern California area is to search for string Backcountry Adventures Southern California on http://www.amazon.com. The book is not bad. It does not contain all trails, but it's good for a starter.

Oleg
Axiom 4WD 2004: OME shocks, 32" BFG Mudders, RockSliderz, OME929+2" spacers, Stinkyfab bent RE rear links, front ARB locker, rear No-Slip locker, DOR front axle lowering kit, custom middle section skid plate, IronMan torsion bars.
Deceased Rodeo'02 4WD.