rock face vs scarp

rock face

noun
  • An exposed, roughly vertical expanse of rock 

scarp

noun
  • The steep artificial slope below a fort's parapet. 

  • A cliff at the edge of a plateau or ridge caused by erosion or faulting; the steeper side of an escarpment. 

verb
  • to cut, scrape, erode, or otherwise make into a scarp or escarpment 

How often have the words rock face and scarp occurred in a corpus of books? (source: Google Ngram Viewer )