Use foam to build up your geographic features first. Then you can use celuclay as your ground work. It works best if its applied in a thickness of no more than 1/4" this way it dries fast enough and evenly so there is little or o curling or distortion that some folks have problems with. Available at craft stores.
As Gino indicated, balsa wood makes great planks and boards. Also available at craft stores, hobby shops, doll house shops etc.
Sifted dirt or sand will make some good texture for your ground work and you can mix in the cheap clay cat litter to replicate rocks and stones.
The roots of woody plants and shrubs make for excellent scale logs. Somewhere in your travels you will no doubt pass a development or someplace where they are clearing and a little foraging will yield some great finds. I usually keep an old set of sheers in my truck so as I travel I can "harvest stuff". The bark of these roots is perfectly in scale and the tendrils or smaller "branch work" is the right size to look in proportion to your figures and scene.
Mike
"Imagination is the dye that colors our lives"
Marcus Aurellius
A good friend will come and bail you out of jail...but, a true friend will be sitting next to you saying, "Damn...that was fun!"
