California Code, Government Code - GOV § 31461.3

(a) The average compensation during any period of service as a member of the Public Employees' Retirement System, a member of a retirement system established under this chapter in another county, a member of the State Teachers' Retirement System, or a member of a retirement system of any other public agency of the state that has established reciprocity with the Public Employees' Retirement System subject to the conditions of Section 31840.2 shall be considered compensation earnable by a member for purposes of computing final compensation for that member provided:

(b) This section shall be applied retroactively under this chapter in favor of any member whose membership in the Public Employees' Retirement System or in a retirement system established under this chapter in any county terminated prior to October 1, 1957, provided that he or she was eligible to and elected deferred retirement therein within 90 days after eligibility for reciprocity, the period intervening between active memberships in the respective systems did not exceed 90 days, or six months if Section 31840.4 applies, and he or she retires concurrently under both systems and is credited with that period of service under the other system at the time of retirement. The limitation of the 90-day or six-month period between the active membership in the two retirement systems shall not apply to an employee who entered the employment in which he or she became a member of the State Employees' Retirement System prior to July 18, 1961; provided he or she entered that employment within 90 days, or six months if Section 31840.4 applies, after the termination of employment in the county system, whether that employment is with the state or with a county, a city, or other public agency that contracts with the Public Employees' Retirement System, the State Teachers' Retirement System, or a retirement system of any other public agency of the state that has established reciprocity with the Public Employees' Retirement System subject to the conditions of Section 31840.2.