The hill in front of you has the appearance of sliding slowly into a jumble. That is exactly what it is doing through a process called slumping.

When the coal vein burned under this area, cracks formed in the hillside. Rain flowing into the cracks weakens the hill, especially where it saturates bentonite clay layers which become slippery when wet. As the bentonite slides, the hill slowly slumps away. 

Slumping happens on a small scale like you see here, but also on a very large scale when entire hillsides slide. The picture above, taken in the North Unit, shows masses of rock that slid from near the top of the canyon, coming to rest far below.