Colo. Rev. Stat. § 37-33-104
When such petition, plat, and bond are filed, the board of directors of said irrigation district in which such improvements are to be made shall proceed at once to view the line of the proposed drainage ditch or drain and the lands affected thereby, and, if in its opinion it is necessary, shall employ an engineer to prepare accurate surveys and estimates of the proposed work and shall set the day and place for hearing all interested parties, receiving protests, information, and any matter in relation to the proposed improvement, and shall notify all resident landowners affected by such improvement by personal service fifteen days prior to the date of such meeting. If personal service of such notice cannot be had, or if any of said landowners are nonresidents, then such notice shall be sent through the mail at least fifteen days prior to said meeting.
C.R.S. § 37-33-104