cliff face vs escarpment

cliff face

noun
  • The very steep, vertical, or overhanging section of rock, earth, or ice slope usually free of any vegetation or loose material. 

escarpment

noun
  • A steep descent or declivity; steep face or edge of a ridge; ground about a fortified place, cut away nearly vertically to prevent hostile approach. 

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