That's a pretty cool looking hillside. My guess would be something like TomTomBinks' guess. I was thinking that large rocks accumulated on the bottom of a river and then later got covered in sediment which hardened. Then the the river bottom got pushed up for some reason.
The other thing which came to mind was that maybe it was an artificial stone wall (human construction) which then fell over or was knocked over. Some of the rocks look flat like they might have been part of a wall.
Where did you find this? What country? State?