Gov. Code, § 31485.10

(a) Notwithstanding any other provision of law, in a county of the 10th class, as defined in Sections 28020 and 28031, the board of supervisors may, by resolution, ordinance, contract, or contract amendment under this chapter, provide any retirement benefits for some, but not all, general members or safety members of a county.

(b) The resolution, ordinance, contract, or contract amendment described in subdivision (a) may provide a different formula for calculation of retirement benefits, by making any section of this chapter applicable to any subgroup of members within a membership classification, including, but not limited to, bargaining units, or unrepresented groups, applicable to service credit earned on and after the date specified in the resolution, which date may be earlier than the date the resolution is adopted.

(c) A resolution adopted pursuant to this section may require members to pay all or part of the contributions by a member or employer, or both, that would have been required if the section or sections specified in subdivision (b), as adopted by the board or governing body, had been in effect during the period of time designated in the resolution. The payment by a member shall become part of the accumulated contributions of the member. For those members who are represented by a bargaining unit, the payment requirement shall be approved in a memorandum of understanding executed by the board of supervisors and the employee representatives.

(d) A resolution adopted pursuant to this section may require safety members hired on and after the effective date of the act adding this subdivision to pay all or part of the contributions by a member or employer, or both. The payment by a safety member shall become part of the accumulated contributions of the safety member. For those safety members who are represented by a bargaining unit, the payment requirement and any changes to the payment requirement shall not be effective until approved in a memorandum of understanding executed by the board of supervisors and the employee representatives.

(e) This section shall only apply to members who retire on or after the effective date of the resolution described in subdivision (a) or (b).

(f) This section shall not become operative unless and until the county board of supervisors, by resolution adopted by a majority vote, makes this section operative in the county.