The idea has some merit, I think. The problem is that Montana's environment has been ravaged by years of mining. The book "Collapse: How Societies Choose to Succeed or Fail" talks about Montana at some length.

There are two somewhat-related problems here with fossil fuels: There's the national-security problem - essentially a political problem, and then there's the environmental problem. Solving one of the two doesn't automatically mean the other is also resolved.

That being said, all options should be on the table to be discussed.