Socal is too big... maybe you can narrow it down to a county at least?
In Thousand Oaks/Newbury Park, you can climb to one of the Peaks in the Santa Monica's. I don't remember the name, but if you want one in that area I can look it up for you. I do remember this as a tough one. Lot's of steep spots, and a good amount of elevation. Probably a 5+ hour hike.
In the OC, just go to Holy Jim, and take the trails to Santiago Peak. It's a mixture of hiking trails and fire roads to get to the top. That's a 10+ hour trek, with 4,000 feet elevation gain.
So many more out there...
