Cal. Rev. & Tax. Code § 60355

All determinations made by the board under this chapter are due and payable at the time they become final. If they are not paid when due and payable, a penalty of 10 percent of the amount of the determination, exclusive of interest and penalties, shall be added thereto. Payment shall be made in the form of a remittance payable to the board and shall be filed with the board together with a copy of the notice of determination which the board shall furnish to the person for that purpose.