cheechako vs sourdough

cheechako

noun
  • Someone new to Alaska or the Yukon; originally, a gold rush newcomer. 

sourdough

noun
  • A type of bread dough leavened with yeast and lactobacilli that produce acids giving a sour taste. 

  • A 49er, a California Gold Rush miner. 

  • An old-timer, especially in Alaska. 

  • A permanent resident of the territory. Someone who has lived in the Yukon during all four seasons. 

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