California Code, Revenue and Taxation Code - RTC § 463

(a) If any person who is required by law or is requested by the assessor to make an annual property statement fails to file an annual property statement within the time limit specified by Section 441 or make and subscribe the affidavit respecting his or her name and place of residence, a penalty of 10 percent of the assessed value of the unreported taxable tangible property of that person placed on the current roll shall be added to the assessment made on the current roll.

(b) Notice of any penalty added to the secured roll pursuant to this section shall be mailed by the assessor to the assessee at his or her address as contained in the official records of the county assessor.

(c) If the assessee establishes to the satisfaction of the county board of equalization or the assessment appeals board that the failure to file the property statement within the time required by Section 441 was due to reasonable cause and circumstances beyond the assessee's control, and occurred notwithstanding the exercise of ordinary care in the absence of willful neglect, it may order the penalty abated, provided the assessee has filed with the county board written application for abatement of the penalty within the time prescribed by law for the filing of applications for assessment reductions.

(d) If the penalty is abated it shall be canceled or refunded in the same manner as an amount of tax erroneously charged or collected.