Colo. Rev. Stat. § 30-6-110
When the boundary lines of any county in this state are so indefinite that a portion of territory, by reason of such indefinite description, is claimed by two counties, and such fact appears by petition of the board of county commissioners of either county to the state engineer, it is the duty of such state engineer, in connection with the county surveyor of each of such counties, to run out and establish such lines as nearly as may be in accordance with such defective description, fix and define such boundary line by monuments in accordance with rules issued by the state board of licensure for architects, professional engineers, and professional land surveyors, and to furnish the board of county commissioners of each of said counties with a description of such line as soon thereafter as may be practical, deposit such survey as a land survey plat in each county, and file a Colorado land survey monument record on each monument found or set, as specified in section 38-53-104. When such line is established it shall be the boundary line between said counties, unless one of said counties, within six months from the day of filing the description of said line by the state engineer with the board of county commissioners of such county, commences an action in a court of competent jurisdiction in this state to determine and settle such disputed line, and prosecute the same with due diligence until its final determination, or has settled such disputed line, within said six months, by arbitration. If the county surveyor of either of such counties shall not appear or assist the state engineer in making such survey after due notice so to do, it shall in no manner affect or invalidate such survey, or the boundary lines as they may be fixed by such state engineer.
C.R.S. § 30-6-110
Rule 109, C.R.C.P., referenced in this section, was repealed March 17, 1994.