Cal. Rev. & Tax. Code § 503

If any taxpayer or the taxpayer’s agent through a fraudulent act or omission causes, or if any fraudulent collusion between the taxpayer or the taxpayer’s agent and the assessor or any of the assessor’s deputies causes, any taxable tangible property to escape assessment in whole or in part, or to be underassessed, the assessor shall assess the property in the lawful amount and add a penalty of 75 percent of the additional assessed value so assessed.