I think I recall something not too long ago about the area being closed to access, but I could be wrong. There was a whole town of sorts out there at one time. If you can still get in there, this would be fun to check out some time.
Edit to add: I just found this on Wikipedia - not sure if it's accurate. Maybe someone in Riverside County can check with the Sheriff's Dept, they should know.
"As of July 18, 2007, the town of Eagle Mountain is no longer openly accessible. The perimeters of both the town and mine have been fenced and gated, with a site manager appointed to handle access requests. The fencing isn't presently visible from either Google Earth or Google Maps, so it's easy to believe that the town is still accessible."
We've camped on the other side of Black Eagle Mine, at the spot where the road into the mining area coming from Joshua Tree is permanently blocked off.
If you like abandoned history stuff, there is a lot to check out in So Cal. Speaking of which, we'll get another Ghost Mountain / Marshal South home site trip going here pretty soon. Talk about weird history.