Colo. Rev. Stat. § 30-5-161
Saguache county: Commencing at the most easterly point of La Loma del Norte; thence in an easterly direction to the point where the Mosco creek enters into the San Luis Valley; thence up the center of said creek to the boundary line of Fremont county, on the summit of the Sangre de Cristo range; thence in a northwesterly direction along the summit of said range to the top of the range at the Poncho pass; thence in a direct line west to the one hundred and seventh degree of longitude; thence south, following said degree, to the north boundary line of Conejos county; thence east along the north boundary line of Conejos county to where it intersects the southwest boundary of Saguache county; thence on a produced southeasterly line to the mouth of the canyon of the snowy range, from whence flows the Rio Grande del Norte; thence down the center of said stream to the place of beginning.
C.R.S. § 30-5-161