Cal. Gov. Code § 21492
The designation of a beneficiary under the optional settlements in Sections 21456, 21457, 21459, 21475, 21475.5, 21476, 21476.5, and 21477, and in Section 21458, if a benefit involving the life contingency of the beneficiary is provided, is irrevocable from the time of the first payment on account of any retirement allowance. Otherwise a designation of beneficiary under this system is revocable at the pleasure of the member who made it. A member's marriage, dissolution of marriage, annulment of his or her marriage, the birth of his or her child, or his or her adoption of a child shall constitute an automatic revocation of his or her previous revocable designation of beneficiary. A member's termination of employment and withdrawal of contributions shall constitute an automatic revocation of the previous revocable designation of beneficiary. Subsequent reemployment or reinstatement from retirement to employment covered by this system shall not reinstate the previous designation of beneficiary.
Upon revocation of any beneficiary designation, a member may designate the same or another beneficiary by a writing filed with the board, except as otherwise provided in Section 21490.
Ca. Gov. Code § 21492