Green’s Dictionary of Slang

(US) an inhabitant of Colorado.

1866		Amer. Citizen (Butler, PA) 26 Sept. 2/4: Nicknames [...] Colorado, rovers.
1871		Cairo Dly Bulletin (IL) 2 Dec. 2/4: Queer are the nicknames of the different states [...] of Colorado, Rovers.
1881		River Press (Fort Benton, MT) 23 Feb. 5/2: Nick-names of the States [...] Colorado, Rovers.
1903		S. Clapin New Dict. Americanisms.
1909		J. Ware Passing Eng. of the Victorian Era.
1952		D. Shulman ‘Nicknames of States and Their Inhabitants’ in AS XXVII:3 184: Rovers for Coloradans.