I got the impression that Pismo is about the only place on the coast with dunes like that were you're allowed to take off-road vehicles on the beach.
The place is really off the wall. You can drive your car or truck right out onto the beach, splash it through the water, or take up through the dunes (although i wouldn't recommend that last one without the right vehicle).
There's all these people out on the beach camping and dirt bikes, dune buggies, and some really bizarre homemade creations flying all over the place.