Colo. Rev. Stat. § 30-5-164
The county of San Miguel is hereby created and established, with the legal capacity and functions of other counties of this state, and with the boundaries as follows:
Commencing at a point on the boundary line between the counties of Hinsdale and San Juan, due east of the junction of Mineral creek and the main branch of the Uncompahgre river; thence due west through said junction to the summit of the divide between Red Mountain valley and Poughkeepsie gulch; thence southerly along said divide, to the divide between the waters of the Animas river and the Uncompahgre river; thence along the divide separating the waters of the Uncompahgre and San Miguel rivers on the north from those of Animas river on the south, to the north line of La Plata county; thence along the north line of said La Plata county to the western line of the state; thence north to the southwest corner of Lake county; thence east along the south line of Lake county to the western line of Hinsdale county; thence southerly along the western boundary of Hinsdale county to the place of beginning.
C.R.S. § 30-5-164