California Code, Evidence Code - EVID § 814

The opinion of a witness as to the value of property is limited to such an opinion as is based on matter perceived by or personally known to the witness or made known to the witness at or before the hearing, whether or not admissible, that is of a type that reasonably may be relied upon by an expert in forming an opinion as to the value of property, including but not limited to the matters listed in Sections 815 to 821, inclusive, unless a witness is precluded by law from using such matter as a basis for an opinion.