Pismo Beach is the go-to location for ATV riding on the sand dunes.  Vendors offer ATV rentals at the beach, or you can drive down the beach to the dunes with your truck and trailer.  Not an environmentally friendly thing to do, but a great experience.  Drive your own vehicle on the beach only if you are experienced and have 4-wheel drive.  The sand is soft, except by the water, and incoming tides can swamp your car.

Do rent an ATV.  Several choices are available.  One vendor provides a shuttle bus from the parking area at the beach to the dune area.  It is about 1-mile down from the main beach.  A good walk.  The staff was helpful and made this ATV first fun for the family. But be aware that this is a dangerous sport and many adults and children wind up at the emergency room.