The wheelchair-accessible Creekside Trail runs parallel to U.S. 16A near the Game Lodge Campground [1]. The hard-surfaced trail follows the Grace Coolidge Creek and connects the Game Lodge Campground and the Grace Coolidge Campground.
The trail covers about two miles and passes by the State Game Lodge [2], the Peter Norbeck Visitor Center [3], the Coolidge General Store, and the park office. It is not uncommon to see buffalo along this trail.
Links:
[1] http://www.moon.com/destinations/mt-rushmore-the-black-hills/the-southern-hills/custer-state-park/campgrounds
[2] http://www.moon.com/destinations/mt-rushmore-the-black-hills/the-southern-hills/custer-state-park/accommodations
[3] http://www.moon.com/destinations/mt-rushmore-the-black-hills/the-southern-hills/custer-state-park/visitors-centers