Okay, let's look at where the truck was found.
In this picture, we can see the bluff rising on the north side of the well site behind the truck. And there's a long, low ridge of rock along the edge of the road on the passenger side of the truck.
Looking on Google Earth, the spot I think best matches the photo above is marked by the yellow balloon. Can't zoom in any closer without losing all detail, but I'm pretty sure that's the same long, low ridge of rock to the left of the yellow balloon.
Zooming out to get a perspective of the area surrounding the well site, we can see the road leading up to it, the large flat clearing where the well once was, and there's the bluff along the north edge of the site.
We know that the final photo of Madyson was taken near rocks above the bluff, "maybe just a couple of hundred yards," according to Sheriff Beauchamp. This could be the line of whitish rocks seen to the north of the bluff, but there's another line of white rocks even further north that seems a better match for this distance estimate.
IMO, it just doesn't make sense that they would drive onto the well site, turn the truck around, drive back onto the beginning of the road, and park the truck there before climbing the bluff and walking to the spot where Madyson's photo was taken.
It seems much more likely that they arrived at the well site and parked near the bluff, climbed up it, walked to the rocks, took the photo, returned to the truck, and began to drive away from the well site. And then whatever happened to them happened.
Sheriff Beauchamp again, from the Disappeared transcript: "It seemed to me like they were leaving, and that someone came up that one-way road, and they stopped. Maybe they knew them, maybe not well. They stopped and talked to the person. From there, obviously, I don't know what happened."
So, there's one thing at least that IB and I agree on.
And here's the video of the drive up the mountain again, if you missed it earlier or just want to review. The rock ridge on the left side of the road can be seen at the 2:10 mark:
http://www.youtube.com/watch?v=dUJJ8E0EFSo
So throw all this into your brain stew and see what cooks up.