Colo. Rev. Stat. § 43-2-139
The board of county commissioners of each county has the power to require all persons placing or maintaining road signs, guide boards, billboards, and bulletin boards, of any kind on any road constituting a part of the county highway system which do not conform to the standards designated by the transportation commission, to remove the same, and if such persons do not comply with such requirements, the board of county commissioners has the power to remove said signs and boards. Where said signs and boards are erected outside the right-of-way of any county road in such a manner that any portion of said sign or board projects onto the right-of-way of said county road, the board of county commissioners has the power to remove as much of said sign or board projecting onto said right-of-way as is necessary to keep said right-of-way free and clear of obstruction.
C.R.S. § 43-2-139