Welcome. Greetings from LA.
While I don't actually camp there, I do "hammock testing" at Biola University because I'm a faculty member there, and campus security won't kick me out! They have a really nice grove of sycamores by the main entrance that are just the right distance apart!
I've not yet been camping with a hammock, since I was driven to hammocks by the extreme discomfort of my last backpacking trip at the end of the summer up in Golden Trout Wilderness! Great place, by the way - but don't tell anyone! Gotta keep the traffic down!
The San Gabriel, San Bernadino and San Jacinto mountains are the closest forest-y places with lots of trees, and thus the closest camping/hanging places. All three have campgrounds and trails that can be hiked, and plenty of trees to hang from.
Beyond that, I'm afraid some of the more experienced SoCal hangers will have to tell us!
Thanks for all the tips!
@Lizzie - that spreadsheet is spectacular!!!
Welcome to ya!