Cal. Government Code § 31813

If this article is effective simultaneously with the effective date of coverage of members under the federal system, the employee and employer federal contributions required with respect to salaries and wages paid for services rendered after the effective date of coverage of such member under the federal system and prior to the time that federal contributions are first deducted from the salaries and wages of such members shall be paid (1) the employee contribution by the county from the member’s accumulated contributions to the extent that such retroactive costs do not exceed one-third of that portion of the member’s contributions under this chapter which is payable with respect to the first three hundred fifty dollars ($350) monthly wage for such retroactive period (2) the employer contributions from contributions made by the county or district during such retroactive period. If the member’s federal contributions payable for such period is greater than the accumulated contributions resulting from one-third of that portion of the member’s contributions under this chapter during such period, which is payable with respect to the first three hundred fifty dollars ($350) monthly wage, the difference shall be paid by the member to the county or district in such manner as may be determined by the Retirement Board. If the federal contributions payable by the member for such period is less than the accumulated contributions resulting from one-third of that portion of the member’s contributions which are payable with respect to the first three hundred fifty dollars ($350) monthly wage, pursuant to the provisions of this chapter for such period, the county or district shall refund the amount of such excess to the member. All refunds made under this section prior to the effective date of the amendments to this section enacted at the 1959 Regular Session of the Legislature are hereby validated and confirmed.