i'd check mtbr.com, pinkbike.com, hell even craigslist for used bikes. you can shop around the local bike shops and see if they have any of last years model on closeout. look at bikes that aren't really cross country or freeride, but more of a trail or the current popular term "all mountain". the geometry of a trail bike is more relaxed and comfortable then a true cross country bike and usually more comfortable to ride. a true cross country bike is made for racing and comes with steeper, more road bike like geometry and will usually have around 3" or less travel. Freeride bikes are burly trail bikes made for hucking off jumps and drops and still be able to pedal.
since you'll be doing more on road riding, a hardtail ( front suspension only) would be a good choice and they're a lot more inexpensive. Just about all the hardtails on the market these days have about 4" (100mm) travel and is more then enough for 90% of the trails in Socal. Whats your budget? you can get good beginner/entry level bikes from the big brands like Trek, Specialized, Cannondale. I would not even consider a bike without disc brakes these days, but you don't need hydraulic brakes as they up the level of difficulty when it comes to adjustments.
if you want to check out some trails in your area, i think sullivan canyon is pretty popular. check out geoladders.com for more trails and maps of the trails in your area.
But I can still climb it up Mathis to Top of the World w/o stopping, and I can make it down any trail you throw at me (Telonics, Smoothies/Mongolia, Ira's... Even most of Valhala)
