Green’s Dictionary of Slang

a newcomer, a novice, esp. a newly arrived immigrant in the mining districts of northwestern North America.

1897		Chicago Record 2 Mar. 4: Many a ‘Checaco’ (tenderfoot) on his way to the mines, with a pack on his back, has thrown down his pack and struck back for town [...] cursing the country and its mosquitos [DA].
1898		Klondike Nugget (Dawson, Yukon Terr.) 20 July 1/4: The usual strong expletives had been used expressive of their meeting and Mr. Chee Chaco was not looking for information from his old friend Mr. Sour Dough [OED].
1905		R. Beach Pardners (1912) 12: ‘Oh, very well,’ says the checkaco, talking like a little girl.
1909		R. Service ‘The Ballad of Hard-Luck Henry’ in Ballads of a Cheechako 67: The supercilious cheechako might designate them high, / But one acquires a taste for them and likes them by-and-by.
1912		J. London Smoke Bellew (1926) 30: ‘What’s chechaquo mean?’ Kit asked. ‘You’re one; I’m one,’ was the answer. ‘Maybe I am, but you’ve got to search me. What does it mean?’ ‘Tender-foot.’.
1917		Boy’s Own Paper XL:2 65: A chechako and a kid and a tin-horn and a piker!
1922		Seattle Star (WA) 18 July 2/5: Should you be a young cheechako seeking a partner [...] you’ll find many others who shake a much more wicked step.
1927		W.R. Morse ‘Stanford Expressions’ in AS II:6 278: sourdough — a man who has been in the country for some time, in contrast to a cheechacho or ‘tenderfoot’ (Alaska).
1939		M. Colby Guide to Alaska xl: Some of the Chinook expressions still used in everyday speech [...] chechakho n. (C.) ‘just arrived,’ hence, tenderfoot.
1940		R. Service ‘The Ballad of the Ice Worm Cocktail’ in Bar Room Ballads (1978) 633: ‘We welcome you,’ he cried aloud, ‘to this the Great White Land. [...] Boys, hail the Great Cheechako!’.
1960, 1975		Wentworth & Flexner DAS.