Cal. Government Code § 20610

(a) Every county superintendent of schools shall enter into a contract with the board for the inclusion in this system of (1) all of the employees of the office of county superintendent whose compensation is paid from the county school service fund other than employees electing pursuant to Section 1313 of the Education Code to continue in membership in a county system; and (2) all of the employees of school districts and community college districts existing on July 1, 1949, or thereafter formed, within his or her jurisdiction, other than school districts that are contracting agencies or that maintain a district, joint district, or other local retirement system, with respect to service rendered in a status in which they are not eligible for membership in the State Teachers’ Retirement Plan. The effective date of each contract shall not be later than July 1, 1949. For the purposes of this part, those school district employees shall be considered employees of the county superintendent of schools having jurisdiction over the school district by which they are employed and service to the district shall be considered service to the county superintendent of schools. (b) If a charter school chooses to participate in the system, all employees of the charter school who qualify for membership in the system shall be covered under the system and all provisions of this part shall apply in the same manner as if the charter school were a public school in the school district that granted the charter.