rock face 
noun
A bare vertical surface of natural rock.The others have been carved from a vertical rock face and are more cave-like....
- The main geographical features of Mugar Gadam, which presumably led to its establishment, are two large, adjacent crevices in the rock face, and above them a nearby spring.
- Wayne easily slipped through the crevice in the rock face, but I had to hold my breath so I wouldn't get stuck.