Colo. Rev. Stat. § 30-26-401
The board of county commissioners of any county in this state may issue negotiable coupon bonds, to be denominated refunding bonds, for the purpose of refunding any of the bonded indebtedness of such county, whether due or not due, or which may become payable at the option of such county, or by consent of the bondholders, or by any lawful means, whether such bonded indebtedness existed on March 30, 1917, or was thereafter created, and there are not funds in the treasury of such county available for the payment or redemption of such bonds; but the amount of such refunding bonds to be issued under the provisions of this part 4 shall first be determined by such board of county commissioners, and a certificate of such determination shall be made and entered in the records of the county prior to the issuance of said refunding bonds.
C.R.S. § 30-26-401