Import a contour map and drape it. The resulting terrain is jagged. Place an FFD lattice over a selected area of the terrain. Pull points down to simulate erosion or tire tracks. This is faster than using the Smoove tool for localized details.
Because you are physically moving UV mapping points, textures often get "smeared" or stretched dramatically. This is fine for conceptual clay models but terrible for final client renders. sketchy ffd sketchup plugin