Colo. Rev. Stat. § 30-5-116
All that section of country now forming a portion of Fremont county, and further described in this section, is hereby created, set apart, and established as the county of Custer, and shall possess all such legal functions and capacities as other counties in this state. The new county of Custer shall be bounded as follows:
Commencing at a point on the summit of the Sangre de Cristo range of mountains where the fourth correction line south, if extended, would cross said range of mountains; thence running east along said fourth correction line to the line between ranges sixty-eight and sixty-nine west of the sixth principal meridian; thence south along said line to the north line of Huerfano county; thence westerly along said north line of Huerfano county to the summit of the Sangre de Cristo range of mountains; thence northerly and northwesterly, along the summit of the Sangre de Cristo range of mountains, to the place of beginning.
C.R.S. § 30-5-116