Colo. Rev. Stat. § 36-4-109
Such actions shall be brought in the name of the state as plaintiff, in the district court of any county in which the system of irrigation or any part thereof is located, or is to be located, and shall make as defendants thereto by proper name and official title, when known, such departmental and other officers, agents, and employees of the United States as have or claim to have jurisdiction, possession, charge, or control, or are exercising the same, over the lands involved or any part thereof, and such other officers, agents, and persons as the board may deem necessary or proper. The summons and other process shall be served and return made in the manner prescribed in articles 1 to 7 of title 38, C.R.S., or in any other manner required by the order of the court in the action.
C.R.S. § 36-4-109