I can't say enough about this great place!
If you are Looking for a nice get-away in So Cal but low on funds, I highly recommend the place! The Whitewater Preserve is open year round (weather permitting) and allows camping for up to 3 nights in any given month for free, though they do appreciate and survive on donations. There are no hook-ups, but tent or self-contained camping in vehicles under 20' allowed. There are restrooms open 24 hours, no trash cans, you are supposed to pack out what you bring in BUT they do have bear-proof dumpsters for campers to place their trash in. Lots of hiking trails, including a trail that meets up with the Pacific Coast Trail that spans from Mexico border to Canada border. Rules and info can be found here if interested: http://www.wildlandsconservancy.org/preserve_whitewater.html
Also, know there is no cell phone service there at all; the ranger station will allow landline phone calls (during business hours) in an emergency. Or you can drive back down the canyon road towards the I-10 about 3.5 miles and you will get your cell service back. No wood/charcoal fires are allowed. You can use gas (propane or butane) grills only.
They also have a crystal clear, stream water fed "Wading Pool" to cool your toes and soul in.