Cal. Government Code § 31490.5

(a) An active member governed by the provisions of this article may elect, by written notice filed with the board, to make contributions and receive credit under this plan for service for which he or she would not otherwise be entitled to receive credit pursuant to this article. (b) Any member who elects to receive service credit pursuant to this section shall have the same purchase rights and shall contribute to the retirement fund the amount that a member in the contributory plan wishing to purchase the same service would have to contribute, based on the rates applicable to a member of the contributory plan with the same date of entry into membership. Payment shall be made by lump-sum payment or by installment payments over a period not to exceed 10 years, prior to the effective date of his or her retirement or, if applicable, prior to the date provided in Section 31485.8. (c) No member may receive any service credit under this section for which he or she has not completed payment pursuant to subdivision (b) before the effective date of his or her retirement or, if applicable, before the date provided in Section 31485.8. Subject to the limitations of federal law, a member who has elected to make payments in installments may complete payment by lump sum at any time prior to the effective date of his or her retirement. (d) Any sums paid by a member pursuant to this section shall be considered to be and administered as contributions by the member. (e) As used in this section, the “contributory plan” means that contributory plan otherwise available to new members of the system on the election date. (f) This section is not operative until the board of supervisors elects, by resolution adopted by a majority vote, to make this section operative in the county.