CAL. EVID. CODE § 1152 : California Code - Section 1152

(a) Evidence that a person has, in compromise or from humanitarian motives, furnished or offered or promised to furnish money or any other thing, act, or service to another who has sustained or will sustain or claims that he or she has sustained or will sustain loss or damage, as well as any conduct or statements made in negotiation thereof, is inadmissible to prove his or her liability for the loss or damage or any part of it.

(b) In the event that evidence of an offer to compromise is admitted in an action for breach of the covenant of good faith and fair dealing or violation of subdivision (h) of Section 790.03 of the Insurance Code, then at the request of the party against whom the evidence is admitted, or at the request of the party who made the offer to compromise that was admitted, evidence relating to any other offer or counteroffer to compromise the same or substantially the same claimed loss or damage shall also be admissible for the same purpose as the initial evidence regarding settlement. Other than as may be admitted in an action for breach of the covenant of good faith and fair dealing or violation of subdivision (h) of Section 790.03 of the Insurance Code, evidence of settlement offers shall not be admitted in a motion for a new trial, in any proceeding involving an additur or remittitur, or on appeal.

(c) This section does not affect the admissibility of evidence of any of the following:

(1) Partial satisfaction of an asserted claim or demand without questioning its validity when such evidence is offered to prove the validity of the claim.

(2) A debtor's payment or promise to pay all or a part of his or her preexisting debt when such evidence is offered to prove the creation of a new duty on his or her part or a revival of his or her preexisting duty.