Badlands formation (4)
I believe the answer is:
mesa
'badlands formation' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mesa that I've seen before include "Isolated flat-topped hill" , "Flat tableland with steep edges" , "High land" , "Flat-topped hill with steep sides, common in the southwestern US" , "Flat tableland with steep sides" .)