Colo. Rev. Stat. § 30-5-146
The county of Montezuma is hereby established, with the legal capacity and functions of other counties of this state, and the boundaries are as follows:
Beginning at the southwest corner of La Plata county, in the state of Colorado, and running thence east along the southern boundary line of said La Plata county to a point on the apex of the ridge dividing the waters of the Rio Mancos from the waters of the Rio La Plata; thence in a northeasterly direction along the apex of said ridge to the southern boundary line of Dolores county, in said state of Colorado; thence west along said southern boundary line of Dolores county to the eastern boundary line of the territory of Utah; thence south along said eastern boundary line of Utah to the place of beginning; and including all that portion of La Plata county drained by the waters of the Mancos river, Bear creek and Dolores river.
C.R.S. § 30-5-146