You live to far away or I would have traded construction work for a hair cut. 
No need to over think this one. No need to use expensive material either. Once you figure out how high you want to go I might suggest using a combination of plywood and foam board. You should be able to get the grade and curves correct by a little trial and error. Then to finish it off use some plaster of paris. You can shape that stuff to make the mountain look like you want.
You can finish it off with that fake snow that comes in a spray can like paint, I think they still make it.
Just remember to keep the grade so the train will not habe any problems climbing.
Sorry if my info sounds so plain but I'm thinking that you want a cool working project and not some complicated year long project. Good luck and I like your idea.
