Cal. RTC § 531.4

When an assessee files with the assessor a property statement or report on a form prescribed by the board with respect to property held or used in a profession, trade or business and the statement fails to report any taxable tangible property accurately, regardless of whether this information is available to the assessee, to the extent that this failure causes the assessor not to assess the property or to assess it at a lower valuation than he would enter on the roll if the property had been reported to him accurately, that portion of the property which is not reported accurately, in whole or in part, shall be assessed as required by law. If the failure to report the property accurately is willful or fraudulent, the penalty and interest provided in Sections 504 and 506 shall be added to the additional assessment; otherwise only the interest provided in Section 506 shall be added.