Colo. Rev. Stat. § 37-28-101
Whenever the owners of lands which may require a combined system of drainage shall unanimously and mutually agree upon a system of drainage and the character of work necessary to be done to drain their lands and the amount of money each shall contribute towards said proposed works, they may reduce their agreement to writing specifying the boundary lines of said voluntary district and the lands therein, in one hundred sixty acre tracts or smaller tracts if necessary, giving the names of the owners of each tract of land specifying the work which they propose shall be done, the name of the drainage district, and also the names of three persons among their number who shall act as directors until the annual election, and they may agree upon any other lawful matter or thing which they may deem pertinent to the work proposed.
C.R.S. § 37-28-101