Cal. Probate Code § 3903

(a) A person having the right to designate the recipient of property transferable upon the occurrence of a future event may revocably nominate a custodian to receive the property for a minor beneficiary upon the occurrence of the event by naming the custodian followed in substance by the words: “as custodian for (Name of Minor) under the California Uniform Transfers to Minors Act.” The nomination may name one or more persons as substitute custodians to whom the property must be transferred, in the order named, if the first nominated custodian dies before the transfer or is unable, declines, or is ineligible to serve. The nomination may be made in a will, a trust, a deed, an instrument exercising a power of appointment, or in a writing designating a beneficiary of contractual rights which is registered with or delivered to the payor, issuer, or other obligor of the contractual rights. (b) A custodian nominated under this section must be a person to whom a transfer of property of that kind may be made under subdivision (a) of Section 3909. (c) The nomination of a custodian under this section does not create custodial property until the nominating instrument becomes irrevocable or a transfer to the nominated custodian is completed under Section 3909. Unless the nomination of a custodian has been revoked, upon the occurrence of the future event, the custodianship becomes effective, and the custodian shall enforce a transfer of the custodial property pursuant to Section 3909.