Last time, I'd just finished the "terraforming" at Dividend - mostly cardboard lattice overlaid with plaster cloth, with foam board profile boards. My next step would typically be to cover the plaster cloth with "ground goop" and, while it was still wet, either sprinkle ground foam on top of it or go directly to applying static grass. But ground goop, being basically a mix of Sculptamold or Celluclay, glue, and paint (click here for details), can be pretty messy. That's usually not a problem - but since I have a cut here, I need to use some rock castings and the goop might mess them up.
Now, if I was as talented as my friend Bill (see his work above - between Goff Brook and Rocky Hill), I could have just carved the rock faces right into the ground goop and called it a day. But, not being as talented, I figured I'd take a more controlled and traditional approach.
So, instead of ground goop, I decided to use rock castings, pressed into plain white Sculptamold, and color and paint everything later.