escarpment vs sierra

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. 

sierra

noun
  • A rugged range of mountains. 

  • A relatively low-quality grade of Spanish saffron. 

  • A scombroid fish. 

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