I have completed several On3 scratch built or craftsman kits. They need stone or rock foundations (circa Colorado 1900). Any ideas or techniques appreciated.
Check out the Chooch flexible cast stone wall sections, You can cut these to the desired height. The come with various sized stones, either random or cut for N through G scale.
The stone foundation in the first picture and the brick foundation in the second were made from Plastruct textured styrene sheets.
I've used textured card stock stone patterns wrapped around foam. I believe they were made by Noch(?). Got them at one of my LHS.
Carve it out of a piece of pink foam -- just like any other stone work.
Here is another way that I have made a stone foundation. First photo shows four assembled sides of a building and four foundation pieces cut from "multi-scale cut block stone wall" http://www.sceneryexpress.com/.../productinfo/FL4150/ from Scenery Express. Note that the foundation pieces, made from urethane, have three courses of stone. The top courses fit into the bottoms of the walls so that two courses remain visible after assembly. Other types of urethane stone wall material suitable for this type of foundation construction are available from Scenic Express.
Don't forget that AmeriTown has foundation stone walls as well.