Colo. Rev. Stat. § 37-41-132
The boundaries of any irrigation district organized under the provisions of this article may be changed in the manner prescribed in sections 37-41-132 to 37-41-148; but such change of the boundaries of the district shall not impair or affect its organization, or its rights in or to property, or any of its rights or privileges of whatsoever kind or nature; nor shall it affect, impair, or discharge any contract, obligation, lien, or charge for or upon which it was or might become liable or chargeable had such change of its boundaries not been made; except that, in case a contract has been made between the district and the United States as provided in section 37-41-113, no change shall be made in the boundaries of the district, and the board of directors shall make no order changing the boundaries of the district until the secretary of the interior shall assent thereto in writing and such assent is filed with the board of directors.
C.R.S. § 37-41-132