Pismo State Beach is the only place in Central and Southern California where you can legally drive on the beach.  The main entrance is at the Oceano Beach Access on Pier Avenue in Oceano, but there is also another entrance at Grover Beach.  Heading south on the beach takes you to Oceano Dunes State Vehicular Recreation Area (SVRA) where you can camp on the beach and explore in your 4×4, dune buggy, ATV, dirt bike, etc.

Links:     CA Parks          List of driving beaches in CA