Colo. Rev. Stat. § 2-2-318
Each member of the general assembly shall be reimbursed for expenses actually incurred pursuant to sections 2-2-316 and 2-2-317. In auditing any mileage claim of members of the general assembly, the controller is authorized to accept without further substantiating evidence the expense voucher duly signed by the member if the mileage in such claim does not exceed the authorized rate at which employees of the executive branch are reimbursed. In addition, he may accept without such further evidence the member's certification as to the number of days of actual attendance under section 2-2-317(1) or, in lieu thereof, the member's certification as to the number of days of actual occupancy under section 2-2-317(2).
C.R.S. § 2-2-318
For mileage allowance for state officers, see § 24-9-104 and § 6 of article V, Colo. Const.