Colo. Rev. Stat. § 31-12-302
A petition signed by not less than twenty percent of the qualified taxpaying electors of such city or town for the dissolution of such city or town and the annexation of the same to the city existing under a special charter may be filed in the office of the clerk of the district court for the county in which the city or town is situated. The petition, or any part thereof, shall be accompanied by an affidavit of one or more of the petitioners showing that the signers are qualified taxpaying electors of such city or town and shall be prima facie evidence of the matters therein set forth. Upon the filing of such petition and upon the consent of the special charter city being shown by published ordinance, the district court shall make an order reciting the substance of the petition and requiring the governing body of such city or town to submit the question of such dissolution and annexation at the next regular election or at a special election of such city or town, as provided in section 31-12-305, to a vote of the registered electors thereof. The order shall be served by delivering a copy thereof to any member of the governing body of such city or town and shall be filed in the office of the clerk of such city or town.
C.R.S. § 31-12-302
This section is similar to former § 31-8-202 as it existed prior to 1975.