If Carleton is of interest, then I’d also look at St. Olaf. It’s in the same town as Carleton, students can take classes at the other university, and I’ve been hearing fabulous reports about the collegial atmosphere there. Whereas Carleton is a reach for nearly all, St. Olaf has a more approachable admissions rate.
Appalachian State, though in the south, does not have the hot and muggy weather stereotypical of the southeast. Lots of biking and trails and other opportunities there.
Colorado State-greater breadth & depth in his areas of interest…but Colorado Mesa in Grand Junction may have better access to outdoors opportunities.
If he’s interested in a small school, Roanoke might be a possibility, and it has lots of trails and other options, nestled between the Blue Ridge Mountains and Shenandoah National Park.
St. Lawrence in NY’s Adirondacks would also be another possibility.
And for another reach-for-all institution, have you considered Williams in MA?