Well, I don't have much experience at most of those trails, but I'm pretty sure they're in one teeny little section of SoCal, somewhere behind the Orange Curtain...
For great places to ride, I'd include:
--Cheeseboro/China Flat/Ahmanson Ranch network in LA/Ventura.
--The Hub in LA
--SART in Berdoo
--Big Laguna Trail/Nobel Canyon in San Diego
--Venice Boardwalk with baby oil and tank top on rad DH bike, in LA.