Cal. Civ. Proc. Code § 843
(b) Unless otherwise stipulated by the parties or ordered by the court, the disclosure made pursuant to subdivision (a) shall be accompanied by a written report prepared and signed by the expert witness if the witness is retained or specially employed by the party offering the expert witness to testify as an expert in the action, or if the expert witness’s duties as the party’s employee regularly involves giving expert testimony. The report shall include all of the following:
(c) If subdivision (b) does not apply to an expert witness because of a stipulation by the parties or an order of the court, the witness’s disclosure shall include both of the following:
(d) Unless otherwise stipulated by the parties, a party shall make the disclosures of any expert witness it intends to present at trial, except for an expert witness presented solely for purposes of impeachment or rebuttal, at the times and in the sequence ordered by the court. If there is no stipulation or court order, the disclosures of an expert witness shall be made as follows:
(f)
(1) A party whose expert witness has made a disclosure pursuant to this section shall promptly supplement or correct the expert witness’s disclosure in either of the following instances: