Cal. Government Code § 11420.30

Notwithstanding any other provision of law, a communication made in alternative dispute resolution under this article is protected to the following extent: (a) Anything said, any admission made, and any document prepared in the course of, or pursuant to, mediation under this article is a confidential communication, and a party to the mediation has a privilege to refuse to disclose and to prevent another from disclosing the communication, whether in an adjudicative proceeding, civil action, or other proceeding. This subdivision does not limit the admissibility of evidence if all parties to the proceedings consent. (b) No reference to nonbinding arbitration proceedings, a decision of the arbitrator that is rejected by a party’s request for a de novo adjudicative proceeding, the evidence produced, or any other aspect of the arbitration may be made in an adjudicative proceeding or civil action, whether as affirmative evidence, by way of impeachment, or for any other purpose. (c) No mediator or arbitrator is competent to testify in a subsequent administrative or civil proceeding as to any statement, conduct, decision, or order occurring at, or in conjunction with, the alternative dispute resolution. (d) Evidence otherwise admissible outside of alternative dispute resolution under this article is not inadmissible or protected from disclosure solely by reason of its introduction or use in alternative dispute resolution under this article.