I have started the scenery base for a mountain. This was a difficult situation because the mountain covers two tracks and eventually a branch line from another module will cross over about 9" above these tracks.
The Area where mountain will be. Note the 3/8" plywood that will surport the track above:
Detail of tunnel. Plaster portals and rock castings will be applies to the foam board surports. The tunnel liner is the only finished surface of the layout at the moment. It is a rock casting inside of a 2" foam block colored with a black wash.
The scenery surport. Waded newspaper above and carboard strips held with hot glue below. -- a open area under the layout was required to matain the two tracks.
The scenery base. Used plaser soaked brow paper bags I found cheap... very strong.
The next step will be to rough out the rock work in plaster soaked paper towel and apply rock castings.