Cal. Educ. Code § 23201

Any person whose accumulated retirement contributions were refunded, who wishes to establish concurrent membership, and who has received, or will qualify to receive, a retirement allowance from one or more of the retirement systems defined in Section 22115.2, may request to redeposit all or a portion of the accumulated retirement contributions that were refunded, with regular interest from the date of refund to the date the system receives the request to redeposit, without being employed to perform creditable service subject to coverage under the Defined Benefit Program.