Nascar,
If you are traveling east on 539, past Luciles and before the enterance to the bombing range look for SF signs on the right. The acutal roads you see here are a bit further in. Most of the roads in the area are most accessable by foot or dual sport motorcyle because they are narrow.
You could also drive into the road which leads to the bombing range and go in on the right by a pit.
Be careful since anything to the west is Bombing Range property. This is the road shown in the above photo.
Here are our tracks for that day. At least Jeff and mine. We had to leave and you can see on our way back to the cars Jeff and I slightly crossed onto the bombing range property because of flooding in our path. The yellow arrows is the property line. No harm done in my mind.