Gov. Code, § 21490

(a) Except as provided in subdivision (b), a member may at any time, including, but not limited to, at any time after reaching retirement age, designate a beneficiary to receive the benefits as may be payable to his or her beneficiary or estate under this part, by a writing filed with the board.

(b) (1) No designation may be made in derogation of the community property share of any nonmember spouse when any benefit is derived, in whole or in part, from community property contributions or service credited during the period of marriage, unless the nonmember spouse has previously obtained an alternative order for division pursuant to Section 2610 of the Family Code.

(2) No designation may be made by an unmarried member who has attained the minimum age for voluntary service retirement applicable to the member in his or her last employment preceding death if that designation is in derogation of the rights of the member’s unmarried, dependent children who are under the age of 18 years at the time of the member’s death.

(c) The designation, subject to conditions imposed by board rule, may be by class, in which case the members of the class at the time of the member’s death shall be entitled as beneficiaries. The designation shall also be subject to the board’s conclusive determination, upon evidence satisfactory to it, of the existence, identity or other facts relating to entitlement of any person designated as beneficiary, and payment made by this system in reliance on any determination made in good faith, notwithstanding that it may not have discovered a beneficiary otherwise entitled to share in the benefit, shall constitute a complete discharge and release of this system for further liability for the benefit.