Here is a link to all the state beaches that allow camping (just look at the SoCal links):

http://www.totalescape.com/active/campstuff/campcoast.html

Here is a link to Doheny’s site:

http://www.dohenystatebeach.org/

Access: 30 miles south of Indio on Highway 111. Located on the northeastern side of the Salton Sea, it is about a three hour drive from the Los Angeles area. The park is located between Highway 10 on the North, and Highway 8 on the South. Highway 111, south of Indio in the Coachella Valley, runs along the lake’s northeast side.
Facilities: 50 sites, some with RV hookups. Restrooms, showers, dump station. Dogs must be kept on leashes no longer than 6′ and in a tent or enclosed vehicle at night. Except for guide dogs, pets are not allowed in park buildings, on trails, or on most beaches. In addition to this campground at the park headquarts, 4 additional campgrounds are located within the park: Mecca Beach Campground, Corvina Beach Campground, Salt Creek Beach Campground and Bombay Beach Campground.
Season: Open year round.
Fees: $ 12 off-season, $ 18 in-season. Fees include entry for 1 vehicle and 1 legally towed vehicle or trailer, additonal vehicles will be charged per night at the park. Campsite assignments are made upon your arrival.