Colo. Rev. Stat. § 30-20-507
As soon as possible after the filing of such petition, the governing body shall fix, by order, a place and time, not less than twenty days nor more than forty days after the petition is filed, for a hearing thereon. Thereupon the clerk of the governing body shall cause notice by publication to be made of the pendency of the petition, of the purposes and boundaries of the proposed district, and of the time and place of hearing thereon. The clerk shall also forthwith cause a copy of said notice to be mailed to each elector of the district at the elector's last-known address, as disclosed by the tax records of the counties and the last official voter registration lists. The clerk shall also cause a copy of said notice to be mailed to each municipality located within three miles of the boundaries of the proposed district at the same time notice is mailed to the electors of the district.
C.R.S. § 30-20-507