After seeing Mt. Rushmore and Custer State Park, we ventured out to the Badlands of South Dakota.  It was an unforgiving land out there.  In fact, we did not keep track of the gas tank, and we were worried about running out of gas.  There was nothing for miles around.  My GPS did not even show a gas station within 40 miles.  Luckily, we saw an old gas station with the non-digital pumps of yesterdays before we entered the Badlands.  You need to watch out for rattle snakes too when hiking in the park.  The rock formations are pretty amazing.