California Code, Probate Code - PROB § 5301

(a) An account belongs, during the lifetime of all parties, to the parties in proportion to the net contributions by each, unless there is clear and convincing evidence of a different intent.

(b) If a party makes an excess withdrawal from an account, the other parties to the account shall have an ownership interest in the excess withdrawal in proportion to the net contributions of each to the amount on deposit in the account immediately following the excess withdrawal, unless there is clear and convincing evidence of a contrary agreement between the parties.

(c) Only a living party, or a conservator, guardian, or agent acting on behalf of a living party, shall be permitted to make a claim to recover the living party's ownership interest in an excess withdrawal, pursuant to subdivision (b). A court may, at its discretion, and in the interest of justice, reduce any recovery under this section to reflect funds withdrawn and applied for the benefit of the claiming party.

(d) In the case of a P.O.D. account, the P.O.D. payee has no rights to the sums on deposit during the lifetime of any party, unless there is clear and convincing evidence of a different intent.

(e) In the case of a Totten trust account, the beneficiary has no rights to the sums on deposit during the lifetime of any party, unless there is clear and convincing evidence of a different intent. If there is an irrevocable trust, the account belongs beneficially to the beneficiary.

(f) For purposes of this section, “excess withdrawal” means the amount of a party's withdrawal that exceeds that party's net contribution on deposit in the account immediately preceding the withdrawal.