Came home too late to get the old painting sticks out but decided to have a bash at getting the tones right on my Wacom tablet. The drawing experience isn't much like real paper but for noodling around and practicing it's pretty awesome.
If you ignore the 'grass' I'm pretty happy. I started with a mid-tone wash and then a slightly darker one to start modeling the shapes of the rocks. I then put in a darker tone still for cracks in the rocks and a final very dark tone for the deep cracks. I then realized that I didn't have the faces of the rocks that were in direct sunlight light enough so went back over with the lightest tone to mark these.
So what did I learn? Well first - I didn't leave the highlights light enough at the beginning so if this was watercolor I'd be out of luck. Second modeling with fairly close mid tones worked well and saving extreme darks for touches here and there gives a good effect. Thirdly I can afford to go 2 or 3 shades darker in the lightest areas when touching in the cracks on the lightest faces. Finally - the rocks look fairly complicated but were actually built our of only a few shapes.