Badlands National Park in south-western South Dakota protects almost 380 square miles of “sharply eroded buttes, pinnacles and spires blended with the largest undisturbed mixed grass prairie in the United States” (quote from Wikipedia). Originally authorized as a National Monument in 1929, it was designated a National Park in 1978.
The North Unit of the Park is easily accessible from Interstate 90 at Wall, South Dakota as shown on the map below.
The photos below were all taken as I drove south and then eastward from Pinnacles Entrance south of Wall, South Dakota until I exited at the Northeast Entrance before returning to I90. If you are visiting in this area Badlands National Park is well worth visiting … the entrance fee in 2017 was $20 for a private vehicle. More information on the park can be found at the National Park Service website