Besides N.Y. City, L.A. and vicinity is the least friendly camp-near-the-beach place I know of. In fact, CA in general has very high coastal restrictions about camping and VERY few RV camps near the beach, pay or not. Having lived in L.A. for 60 years I don't know why anyone would want to visit the place. I got out as quickly as I could.
That being said, there are places that you can 'camp' ON the sand in CA.
1. Pismo Beach. California's token beach sand playground. Huge area. You had better have 4WD and lower the pressure on your tires or you will sink up to your headlights.
2. Point Sal, north of Vandenburg A.F. Base. A small piece of beach with a narrow zig-zagging two track to the beach. I attempted this during the winter one year, slipped off the gooey road, and got my Land Cruiser stuck in the ditch trying to get there. We spent the night sitting up in a rainstorm at a 45degree angle. Winched out the next AM. So, pick your season well. It's a hidden gem of a beach camping opportunity. Here we're camped in 1967:
3. Usal Beach in Northern CA. You go down a dirt track cut into the coastal hillsides for miles and get to abandoned Usal State beach and can camp right on the high tide line. It is wonderful. Best in September/early October.
4. Jalama Beach County Park, near Lompoc,CA. This is another hidden gem; you will get lots of sea sounds here. Part of it backs on to the coastal dunes. Magic.
5. Several Oregon state beaches have an 'ocean tone' with the campsites and are the best sea side state beaches on the planet, IMHO. We were there all last week. There is a commercial camp parking lot in So. Oregon that you can back your TC right to the tidewater sand.
regards, as always, jefe