Cal. Gov. Code § 20509
When a school district ceases to exist and is succeeded by, or the territory thereof is attached to, another school district that is a contracting agency, the contract under which the contracting agency participates in this system shall be considered, with respect to the former district and its employees, a continuation of the contract under which the former district participated, with the changes as the succeeding contract contains. The board shall determine the amount of accumulated contributions held under the contract of the county superintendent of schools which had been made by the former district, and the contributions shall be transferred to the credit of the contract under which the succeeding district participates.
Nothing in this section or Section 20508 shall authorize a school district, the formation of which becomes effective for all purposes after October 1, 1961, to participate in this system except as provided in Chapter 6 (commencing with Section 20610).
Ca. Gov. Code § 20509