A cheechako is a person who is a tenderfoot, a newbie -- the term dates from the Klondike Gold Rush of the 1850s in Alaska and the Yukon. Daniel Pinkwater quotes a friend living in Alaska as saying the word is an Upik pronunciation of "Chicago," but I can find no confirmation of this, and in fact a web site I found explains the word as "combining the Chinook Indian word 'chee,' meaning new, fresh, or just now, with the Nootka Indian word 'chako,' which means to come, to approach, or to become."

But whatever the source, the new people coming up from points further south, inexperienced in mining or surviving Alaskan winters, were called "cheechakos," and the word found its way into the works of Jack London and Robert Service, and it's still used in the area to describe newcomers. (It also seems to be used as a name for stores and tour companies.) After a certain amount or time or experience, one becomes a "sourdough."

http://www.lifeinak.com/glossary.htm http://www.zianet.com/sunny/html/untitled_2_3.html
Daniel Pinkwater, Hoboken Fish and Chicago Whistle, 1999, page 88.