C.R.S. § 31-2-303

The mayor or, if there is no mayor, the presiding officer of the governing body, immediately upon the effective date of the ordinance or resolution, shall cause notice to be given of the election, of the question to be submitted thereat, and of the time and place of the holding thereof, which notice shall be published once each week for four consecutive weeks in some newspaper of general circulation within the city or town. If there is no such newspaper, publication shall be by posting a copy of said notice in three public places within the municipal limits.