Cal. Prob. Code § 6321

An instrument may designate as a primary or contingent beneficiary, payee, or owner a trustee named or to be named in the will of the person entitled to designate the beneficiary, payee, or owner. The designation shall be made in accordance with the provisions of the contract or plan or, in the absence of such provisions, in a manner approved by the insurer if an insurance, annuity, or endowment contract is involved, and by the trustee, custodian, or person or entity administering the contract or plan, if any. The designation may be made before or after the execution of the designator’s will and is not required to comply with the formalities for execution of a will.