Colo. Rev. Stat. § 31-31-708
Any county that does not cover, under the federal "Social Security Act", as amended, salaried employees whose duties are directly involved with the provision of law enforcement or fire protection as certified by the county may elect coverage under the statewide retirement plan established in article 31.5 of this title 31 and the statewide death and disability plan established in part 8 of this article 31 by filing a resolution of affiliation with the board. Election of coverage under the plan is irrevocable. Such participation shall be as provided by rules adopted by the board. The board may determine a continuing rate of contribution for all members who are active on the effective date of coverage to fund benefits as may be necessary to ensure that the affiliating employers' coverage shall not have an adverse financial impact on the actuarial soundness of the plan.
C.R.S. § 31-31-708