Cal. Ed. Code § 1313
Each county employee whose status is changed by this article, and who is in employment and a member of a county retirement system other than one provided by contract with the Public Employees' Retirement System on the date of the change, shall become eligible for membership in the Public Employees' Retirement System in accordance with the Public Employees' Retirement Law with respect to his or her employment thereafter, and shall be subject to the reciprocal benefits provided by those systems. However, the employee may elect to continue in membership of the county retirement system with respect to his or her employment thereafter, in which event the same appropriations and transfers of funds shall be made to the retirement fund of the county system for the employee as those required of the county under the county retirement law, and these amounts shall be legal charges against the county school service fund. The election authorized by this section shall be made no later than the date preceding the date upon which his or her status is changed in accordance with procedures to be established by the county board of supervisors, which shall allow at least 30 days to make the election. The election once made shall not be rescinded. An employee who does not elect to continue membership in the county system shall be deemed to have discontinued county employment for purposes of the county system at the close of the day preceding the date upon which his or her status changes.
Ca. Educ. Code § 1313