“ Bad Lands occur on arid plateaus formed by horizontal strata of loosely cemented sands and gravels. In these regions rain falls only during short periods, but then the storm waters erode the incoherent rock that is unprotected by vegetation, resulting in the formation of a labyrinthine series of valleys of all sizes, most of which are dry ‘arroyos’ during the greater part of the year. ”

“ When the erosion is carried to its extreme limit the greater part of the region is reduced to base-level, and isolated fragments of the old plateau rise above this to form table mountains, or ‘mesas.’ The best examples of Bad Lands are found in the upper portion of the Missouri drainage basin, in the vicinity of the Black Hills. ”