Well, it's been a very long time, but I finally got to it and was able to find a suitable mixture between plaster of paris, water, and vinegar. Paper towels were also used. The attached picture is the result. I made the hill higher than originally. I would like to have a rock face (sort of what it looks like when you cut through a section of mountain). What I have now does not look like a rock face at all. Any tips on how to carve the plaster or leave marks in a way that it will look like a rock cliff? Once I get that out of the way then I'll try my luck at painting it. Thanks for all your tips.