These rock spires are a favourite of mine - easy and cheap to make, useful in game play, and suitable for all the game systems!
1 inch thick styrofoam sheet or offcuts of polystyrene from packing cases
Bamboo barbeque skewers
Base material such as thick corrugated cardboard or wood.
Insert as many bamboo skewers as you want spires through the base material and glue in place
Cut styrofoam chunks of varying thickness and size and push them onto the bamboo skewers to make a styrofoam kebab (yummy!). Spread PVA glue between the layers of the kebab as you add them. Use a thin piece of card or styrofoam to make a platform between two spires here and there.
Melt the surface of the styrofoam with a hot knife, soldering iron or solvent to get a rough rocky finish
Paint dark grey and drybrush with lighter grey and then a light white drybrush