Grassland on top that has never been grazed or ploughed
Two flat-topped mesas standing about a mile apart in the western badlands, in and around the Little Missouri National Grasslands. They were made National Natural Landmarks in 1965 for a reason you cannot see from a distance: the tops have never been grazed or cultivated, so the grassland up there is the real thing, a rare piece of plains that no animal or plough has ever been turned out on.
Other places on the map within a couple of hours of here.