California Code, Revenue and Taxation Code - RTC § 408.2

(a) Except as otherwise provided in Sections 63.1, 69.5, 451, and 481 of this code and in the provisions listed inSection 7920.505 of the Government Code, any information and records in the assessor's office that are required by law to be kept or prepared by the assessor, other than homeowners' exemption claims, are public records and shall be open to public inspection.  Property receiving the homeowners' exemption shall be clearly identified on the assessment roll.  The assessor shall maintain records that shall be open to public inspection to identify those claimants who have been granted the homeowners' exemption.

(b) The assessor may provide any appraisal data in the assessor's possession to the assessor of any county and shall provide any market data in the assessor's possession to an assessee of property or an assessee's designated representative upon request.  The assessor shall permit an assessee of property or an assessee's designated representative to inspect at the assessor's office any information and records, whether or not required to be kept or prepared by the assessor, relating to the appraisal and the assessment of the assessee's property.  Except as provided in Section 408.1, an assessee or an assessee's designated representative, however, shall not be provided or permitted to inspect information and records, other than market data, which also relate to the property or business affairs of another person, unless that disclosure is ordered by a competent court in a proceeding initiated by a taxpayer seeking to challenge the legality of the taxpayer's assessment.

(c) The assessor shall disclose information, furnish abstracts, or permit access to all records in the assessor's office to law enforcement agencies, the county grand jury, the board of supervisors or their duly authorized agents, employees, or representatives when conducting an investigation of the assessor's office pursuant to Section 25303 of the Government Code, the Controller, probate referees, employees of the Franchise Tax Board for tax administration purposes only, the State Board of Equalization, and other duly authorized legislative or administrative bodies of the state pursuant to their authorization to examine the records.

(d) For purposes of this section, “market data” means any information in the assessor's possession, whether or not required to be prepared or kept by the assessor, relating to the sale of any property comparable to the property of the assessee, if the assessor bases the assessment of the assessee's property, in whole or in part, on that comparable sale or sales.  The assessor shall provide the names of the seller and buyer of each property on which the comparison is based, the location of that property, the date of the sale, and the consideration paid for the property, whether paid in money or otherwise, but for purposes of providing market data, the assessor shall not display any document relating to the business affairs or property of another.

(e) This section applies only to a county with a population that exceeds 4,000,000.