US ravine (5)
I believe the answer is:
gulch
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">us ravine</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(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" .)