I apply a regular rock preset shader to the rocks and make it a master shader. Then I click on the displacement tab and pick an Enhance C filter from the dropdown menu of available shaders and filters and apply it. Every "rock formation" I apply the master shader to now will get the same kind of displacement. I also used a flat terrain and some low-poly rocks and applied the same master shader to them. This is just a quick-and-dirty scene to show what kind of effects you can get. I would take alonger time to carve out the bottom of the river bed for an actual scene,lol.