I went to Cal Poly so im quite familiar with this area. There's a great trail up there near lake Lopez to a trailhead called little falls. It's about 8 miles round trip of wheeling through a creek bed (w a 35 min drive to trailhead). Might make for a great day outing beyond the dunes. I used to somehow wheel it with my ranger back in the day. It's really fun with all the creek crossings.