The Collaborative International Dictionary of English v.0.48:

Bad lands \Bad" lands"\
   Barren regions, especially in the western United States,
   where horizontal strata (Tertiary deposits) have been often
   eroded into fantastic forms, and much intersected by
   ca[~n]ons, and where lack of wood, water, and forage
   increases the difficulty of traversing the country, whence
   the name, first given by the Canadian French, Mauvaises
   Terres (bad lands).
   [1913 Webster]

WordNet (r) 3.0 (2006):

Bad Lands
    n 1: an eroded and barren region in southwestern South Dakota
         and northwestern Nebraska [syn: Bad Lands, Badlands]