Cal. Fin. Code § 6805

The pledge or hypothecation to any association or federal association of all or part of a multiple party account, as defined in Section 5132 of the Probate Code, signed by any one or more tenants, whether minor or adult, upon whose signature or signatures withdrawals may be made from the account shall, unless the terms of the account provide specifically to the contrary, be a valid pledge and transfer to the association or federal association of that part of the account pledged or hypothecated, and shall not operate to sever or terminate all or any part of the account.