Jeremy and I went to the Algodones Sand Dunes off of Interstate 8 at Gray's Well, CA about a half hour's drive from the Arizona border. This huge dune field is one of the locations where they filmed Star Wars scenes for Luke's planet, Tatooine.
The dunes here are beautiful with big bowls and high ridges. We went for long rides on ATV Quads. It is a surreal experience being surrounded by hills of sand as far as the eye can see.
During the heat of the day, we ended up swimming in the canal that carries water from the Colorado River to the large farms of Imperial County.