Colo. Rev. Stat. § 43-2-216
When the board of county commissioners of such county has determined and approved, by resolution of the board, any highway project for the construction, repair, or improvement of highways within its territorial limits, either by the county itself or with the department of transportation of the state of Colorado and with or without federal aid so as to determine the cost thereof or the share of such cost to such county to be approved by such county, it may by resolution authorize the issuance of anticipation warrants in such amount as may be necessary to raise funds sufficient to defray costs of the same, said warrants thereupon to be delivered to the county treasurer and by him offered for public sale at not less than par. The aggregate of such warrants outstanding shall not exceed ten percent of the valuation for assessment of all property of said county as of the date of issuance thereof. No warrants shall run for a period longer than ten years before retirement nor bear a rate of interest in excess of four percent.
C.R.S. § 43-2-216