California Code, Probate Code - PROB § 5401

(a) Financial institutions may enter into multiple-party accounts to the same extent that they may enter into single-party accounts. Any multiple-party account may be paid, on request and according to its terms, to any one or more of the parties or agents.

(b) The terms of the account or deposit agreement may require the signatures of more than one of the parties to a multiple-party account during their lifetimes or of more than one of the survivors after the death of any one of them on any check, check endorsement, receipt, notice of withdrawal, request for withdrawal, or withdrawal order. In such case, the financial institution shall pay the sums on deposit only in accordance with such terms, but those terms do not limit the right of the sole survivor or of all of the survivors to receive the sums on deposit.

(c) A financial institution is not required to do any of the following pursuant to Section 5301, 5303, or any other provision of this part:

(d) All funds in an account, unless otherwise agreed in writing by the financial institution and the parties to the account, remain subject to liens, security interests, rights of setoff, and charges, notwithstanding the determination or allocation of net contributions with respect to the parties.