Colo. Rev. Stat. § 31-21-401
On the petition of a majority of the registered electors of any city or town having an outstanding bonded indebtedness amounting to one-fourth or more of its valuation for assessment, the governing body of such city or town is authorized to levy or cause to be levied at one time a tax on all the taxable property subject to taxes for payment of such bonds sufficient to discharge the entire principal of and the accrued interest on such indebtedness plus fifteen percent for delinquencies, which tax may be paid by the property owners at one time or in installments, as provided in this part 4. In determining the amount of outstanding bonded indebtedness, any sum in the sinking fund may be deducted.
C.R.S. § 31-21-401
This section is similar to former § 31-21-401 as it existed prior to 1975.