Colo. Rev. Stat. § 37-43-172
Immediately upon the making of such order by said district court, the clerk of such court shall issue a notice of such order, in the nature of a summons, under his hand and the seal of such court, notifying all persons included within such order of the contents thereof, which notice may be served either personally in the same manner as provided for the service of summons under the Colorado rules of civil procedure, or by publication once a week for three successive weeks in some newspaper, to be designated in such order, of general circulation published in the county where such court is held, or, in case there is no such newspaper, then by posting the same in at least three conspicuous places in such county, to be designated by such order, one of which places shall be within the boundaries of such irrigation district, and by mailing a copy of such published notice, by registered mail at least thirty days before the date of any such hearing, to each of the creditors and bondholders of the district and their representatives and attorneys, insofar as known to or ascertainable by the court.
C.R.S. § 37-43-172