Cal. Health & Safety Code § 81010

(a) The following evidence is not admissible as evidence in any civil or criminal proceeding, including a subrogation action by the state pursuant to Article 7 (commencing with Section 81030), to establish the liability of any person for any damages alleged to have been caused by a release of a hazardous substance:
1. (1) A final decision made by the Department of General Services pursuant to this chapter.
2. (2) A decision made by the Department of General Services to admit or not admit any evidence.
3. (3) Any finding of fact or conclusion of law entered by the Department of General Services in a proceeding for a claim pursuant to this chapter.
4. (4) The fact that any person has done any of the following in a proceeding for a claim pursuant to Section 80920:
  1. (A) Chosen to participate or appear.
  2. (B) Chosen not to participate or appear.
  3. (C) Failed to appear.
  4. (D) Settled or offered to settle the claim.
(b) Subdivision (a) does not apply to any civil action or writ by a claimant against the Department of General Services for any act, decision, or failure to act on a claim submitted by the claimant.