Do a Google Maps view of the USA and then use the satellite view and zoom down onto individual states. Lots of open space and also lots of mountains, true mountain ranges with a height of more than a mile.
I only recently learned that 38% of Idaho is forested, more than any other state by a wide margin. With forests you get cleaner running streams and more wildlife.
You can do a first trip and fly to Arizona or San Francisco or elsewhere in the west and rent an RV for a couple weeks. Not at all difficult way to get some experience and widen your friend's perspective.