The expandable foam over chicken wire sounds like a great idea. You could sculp the Rockies and have a cabin or two here and there. A real water stream flowing over and down the rocks would seem a natural for this environment. Plus you wouldn't have to worry about the usual things that cause problems: causing too much humidity. (Heck, you've got the entire world's atmoshere to absorb the water molecules.)
Then of course if it rains often enough to suit your operations, the sytem is automatic. Otherwise it would be easy to supplement the water flow with a garden hose. If it snows a little, you will have an absolutely fabulous natural Scene of the Rockies. If it doesn't snow where you are located, perhaps you could rent on of those snow making guns. Might be overkill.
I'm not sure about the astroturf seems like you'd have a perfectly manicured summer lawn in the middle of the winter. I'd go with rugged painted and sculpedted mountains, with some trees and bushes of a brownish-gray cole.
Just for what it's worth. Sure sounds like fun.