From the satellite view of the visitor center there, it does look like you have to make sure to "hit your marks" when exiting the parking lot in a large rig.
When I first looked at the picture, it seemed like maybe the driver was trying to take a short cut out of a parking lot - but the Facebook thread has a response by the City of Rocks National Reserve that says they were existing the visitor center, so I would believe that they were leaving from a legitimate exit.
So now I think that the driver just cut it too close. Maybe the driver was trying to keep from going too far into the opposite lane. In my opinion, and like other things, everybody has one - the driver should have exited as far to the left as they could have, and should have driven straighter out before turning. Which if turning like that, looks like it would have placed the front, drivers side tire on the edge of the far side of the road - and that looks like it does ditch downwards as well.
I wonder if the driver was trying to prevent knocking the front end of the motorhome into the ditch and in doing so, buried the back end in one.
Definitely a bad day for them. I hope they have CoachNet or Good Sam because they're not getting out of that ditch without them. Look how the body is completely offset over the rear axle.
There's quite a bit of visible damage - the windshield is pretty significantly popped out, the bay doors have been scraped by the road and rocks, the bay doors are tweaked (look at the graphics, although that might reset when its on level ground again), and who knows what under carriage damage was done.
Certainly a crappy way to start or end a visit to the reserve.