US ravine (5)
I believe the answer is:
gulch
'us ravine' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for gulch that I've seen before include "American ravine" , "Narrow ravine (Amer.)" , "valley" , "Narrow ravine (US)" , "A narrow gorge with a stream running through it" .)