California Code, Revenue and Taxation Code - RTC § 481

All information requested by the assessor or the board pursuant to this article or furnished in the change in ownership statement shall be held secret by the assessor and the board. All information furnished in either the preliminary change in ownership statement or the change in ownership statement shall be held secret by those authorized by law to receive or have access to this information. These statements are not public documents and are not open to inspection, except as provided in Section 408.