back forty vs expanse

back forty

noun
  • The most remote or inaccessible part of any place. 

  • The remote part of a farm. 

expanse

noun
  • A wide stretch, usually of sea, sky, or land. 

  • An amount of spread or stretch. 

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