Most of the hills on my layouts are made from stacked and carved layers of extruded pink foam covered by Mold-a-Scene plaster, cast plaster from rock molds, and pieces of urethane stone-faces.
The first two photos show the tunnel/hill on my 10’-by-5’ layout. Some plaster rock-mold castings were glued into the Mold-a-Scene. The rocks at the bottom are urethane stone-faces. The entire hill/tunnel lifts off the layout to make it transportable and for track access in the tunnel.
Next photo shows the northeast corner of my 12’-by-8’ layout. Same technique including some plaster castings.
Next photo shows the north hill on my 12’-by-8’ layout – the first that I did. The interior is a balsa wood egg-crate covered with plaster cloth, Mold-a-Scene and plaster castings.
Remaining photos show the hills at the south side of my 12’-by-8’ layout. All of them are layers of stacked and carved extruded pink foam covered with Mold-a-Scene.
I have not tried applying plaster to carved foam and then carving the plaster, but I think that’s probably the best way to get realistic rock-faces and crevasses. Mold-a-Scene does not lend itself to carving stone-faces.
MELGAR