plateau vs upland

plateau

noun
  • A largely level expanse of land at a high elevation; tableland. 

  • A comparatively stable level after a period of increase. 

  • A notable level of attainment or achievement. 

verb
  • (of a varying quantity) To reach a stable level after a period of increase; to level off. 

upland

noun
  • The area in the interior of a country with a generally higher elevation. 

adj
  • Of, relating to, or situated in the uplands. 

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