Colo. Rev. Stat. § 40-20-110
In any written contract for the sale of railroad equipment or rolling stock, deliverable immediately or subsequently, at stipulated periods, by the terms of which the purchase money, in whole or in part, is to be paid in the future, it may be agreed that the title to the property so sold or contracted to be sold shall not pass to or vest in the vendee until the purchase money has been fully paid or that the vendor shall retain a lien thereon for the unpaid purchase money, notwithstanding delivery thereof to and possession by the vendee for a period not to exceed twenty-five years in any one contract, which terms shall be expressed in said contract; but the situs or location of all such property shall, for the purposes of taxation and revenue, be deemed to be within the state of Colorado.
C.R.S. § 40-20-110