Colo. Rev. Stat. § 39-11-122
Any county in this state having in its possession or under its control certificates of purchase resulting from the sale of a tax lien on land for the nonpayment of general taxes may assign, sell, or transfer such certificates in such manner, at such times, and on such terms as may be determined by resolution of the board of county commissioners of such county. Thereafter such county shall execute and deliver such instruments as may be necessary fully to convey all of the right, title, and interest of the county in or to such certificates; but no sale of any certificate of purchase issued upon any real estate upon which taxes in excess of ten thousand dollars are then due shall be valid unless and until the sale of said certificate and the terms of said sale are approved by the administrator after notice of said proposed sale and the terms thereof have been published in at least one issue of a newspaper published regularly in the county where said real estate is located, or if no newspaper is published in said county, then by posting notice of said proposed sale and the terms thereof at the county courthouse and two other public places in said county.
C.R.S. § 39-11-122