the Hat Creek Breaks of Wyoming

Just north of Lusk in Niobrara County Wyoming, one passes over a rim towards the Black Hills of South Dakota and NE Wyoming.

One must go down to go back up unlike the Rockies where the Great Plains generally rise toward the mountains. In essence you are stepping down the great terraces of the Great Plains and the Black Hills are one of the abnormalities found on the surface of the earth, nature has no need for regularity, it's what makes life so abundant and special.