Colo. Rev. Stat. § 13-25-108
In all actions in all courts of record, the original assessment, or a certified copy thereof purporting to be made by the corporate authorities of any municipality in this state, under a statute authorizing the same, which determines the cost and expense due from any piece of real estate, or from the owner thereof, because of the construction of any kind of local improvement in the taxing district wherein such property is located, or in front of, abutting upon, or adjacent to said realty within any such municipality shall be accepted and treated by such tribunals as prima facie evidence of the lawful existence, and due and proper performance of all preliminary steps essential to make such assessment a legal and valid assessment against the realty or owner thereof, or both, against whom it appears to be made.
C.R.S. § 13-25-108