How far across are the Badlands of South Dakota at a place narrow enough to walk across?|181469

I know the entire Badlands goes a long way, but is there anywhere I can use in a book I_m writing where my character can go down the Wall (the cliff) onto the Badlands, and walk across a distance of, say, 4 miles?

You cannot walk on the Badlands except on designated trails:


http://www.badlands.national-park.com/hi��