California Code, Government Code - GOV § 31680.8

(a) Notwithstanding any other provision of law, a safety member who was required to retire for service because of age during the operative dates of, and as described in, Section 31662.4, 31662.6, 31662.8, or 31663, may be reemployed by the county in the same position that he or she retired from and be reinstated to active membership upon all of the following:

(b) The member shall be reinstated to active membership in the plan or tier that he or she retired from, effective the first day of the month following the date of reemployment, and his or her membership shall be the same as if unbroken by retirement.  Notwithstanding any other provision of law, the credited service of the member rendered both before and after reinstatement shall be included for the purpose of determining the eligibility of the member for benefits under this chapter.

(c) Upon reemployment pursuant to this section, the retirement allowance of the member shall be cancelled.  Upon the subsequent termination of the member from employment, the retirement allowance of the member shall be recalculated on the basis of the credited service rendered both before and after reinstatement pursuant to the formula applicable to the member prior to reinstatement.  Notwithstanding any other provision of law, the reinstatement rights conferred by this section shall not entitle a person to a retirement right or benefit that exceeds the limitations in the Internal Revenue Code that apply to public retirement systems.

(d) Upon reinstatement pursuant to this section, the rate of contribution of the member shall be based on the same age at entry that was used in calculating the contribution rate of the member during his or her original period of employment.

(e) This section shall apply only to a county of the first class as described in Section 28020 and shall not become operative in that county until the board of supervisors, by resolution adopted by majority vote, makes this section operative in that county.