Bolster vs Keystone

Bolster

name
  • A ghost town in Okanogan County, Washington, United States. 

  • A surname from German. 

Keystone

name
  • A ghost town in North Dakota. 

  • A city and town in Iowa. 

  • A town in South Dakota. 

  • A census-designated place in Colorado. 

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