The rocky crags in the background are little more than spray painted mattress foam! Using chunks of foam that are fairly thick (whatever you want your plateau height to be), rip little trenches out along the sides using your fingers. Ideally, start with tan colored foam. Spray paint them with rust. Spray paint brown or black along the bottom edges. Finish off with a bit of yellow on the top and some light dusting with white spray for highlights. Foam rubber is much nicer than styrene foam since it doesn't melt under spray paint, and is very springy and doesn't crumble. You can see more plateaus behind all of my Gorka Morka scenery.