Thanks for that.

You might find this useful as well,

http://www.exo-terra.com/en/products/sand_mat.php

In effect its a mat of sand and gravel glued to a fabric base for terrariums.

I use it cut into irregular shapes as rough terrain areas, though I do give it a coat of paint to consolidate the sand and match other terrain features. I guess you wouldn't need to paint it if you didn't want to.