Colo. Rev. Stat. § 30-5-133
Jefferson county is hereby bounded as follows:
Except for those portions that became part of the city and county of Broomfield on November 15, 2001, in accordance with sections 10 to 13 of article XX of the state constitution, commencing at a point where the township line between townships one and two south intersects the range line between ranges sixty-eight and sixty-nine; thence due west twenty miles; thence due south to the junction of North and South Clear creeks; thence south to the Platte river; thence down the center of said Platte river to the point where said river intersects the first correction line; thence west to the range line between ranges sixty-eight and sixty-nine; thence north to the place of beginning.
C.R.S. § 30-5-133
Pursuant to §§ 30-6-105 to 30-6-109, inclusive, there is recorded in the office of the clerk and recorder of Park County in book 70, page 560, and in the office of the clerk and recorder of Jefferson County in book 140, page 400 (indexed in book 2 - Miscellaneous Papers - in the office of the secretary of state), a proclamation showing attachment to Park County and detachment from Jefferson County of territory described as follows:
"Beginning at the intersection of the boundary line between Park and Jefferson Counties with the center line of the South Platte River, about two miles above Lake George, thence down the said Platte River along its center line to intersection of said center line with the Second Correction Line South, thence westerly along said Correction Line to its intersection with the boundary line between Park and Jefferson Counties, thence along said boundary line to point of beginning."