escarpment vs piedmont

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. 

piedmont

noun
  • Any region of foothills of a mountain range. 

adj
  • Formed or lying at the foot of a mountain range. 

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