Dave, we camped at Senators Wash (Imperial Dam) from 1995 to 2012 and really loved the area. Lots of room to camp and spread out. We did a lot of hiking, but not SxS riding. It is a vast area and I'm sure there are lots of riders there.
Close enough to Yuma for supplies, and dates and date shakes at Bard. The Army Proving Grounds are adjacent to Senators Wash and is open to the public and if you are a vet there is a small PX. Also, a Chapel where we worked with the Chaplain with our music ministry.
A great area, I highly recommend it. Just go south on 95 from where you are and turn west at the "big guns". Stop and take a look at the equipment there.