I can't speak for the south end of your route, but as you get near Mt. Rushmore, check out Custer State Park. It's huge, has several campgrounds, and is just lovely, and you'll see as many bison, wild burros, and other wonderful wildlife as you desire. You'll need reservations, so investigate soon if you think you want to go there.
Judy Bass
Altadena, CA
Roadtrek 93 Pop