• 11.021 He would do nothing but sit with his back to the rock-face
• 11.032 and fell on the smooth rock-face.

Its own main entry, with or without hyphens, in OED.

“rock face, n.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/275103. Accessed 19 September 2017.