Cal. Code of Civil Procedure § 1258.280

Except as provided in Section 1258.290, upon objection of a party who has served his list of expert witnesses and statements of valuation data in compliance with Section 1258.230: (a) No party required to serve a list of expert witnesses on the objecting party may call an expert witness to testify on direct examination during his case in chief unless the information required by Section 1258.240 for such witness is included in the list served. (b) No party required to serve statements of valuation data on the objecting party may call a witness to testify on direct examination during his case in chief to his opinion on any matter listed in Section 1258.250 unless a statement of valuation data for such witness was served. (c) No witness called by a party required to serve statements of valuation data on the objecting party may testify on direct examination during the case in chief of the party who called him to any opinion or data required to be listed in the statement of valuation data for such witness unless such opinion or data is listed in the statement served except that testimony that is merely an explanation or elaboration of data so listed is not inadmissible under this subdivision.