Cal. Gov. Code § 20991

Any member who was absent on military service and whose contributions are not paid for him or her by his or her employer as provided in Section 20997, may make the contributions upon his or her return to state service at times and in the manner prescribed by the board. If he or she does so contribute, he or she shall receive credit for the absence as state service in the same manner as if he or she had not been absent from state service.