California Code, Revenue and Taxation Code - RTC § 11319

If any assessment made pursuant to this article results in a tax that is paid after December 10 of the year to which the assessment relates, the tax shall bear interest at the adjusted annual rate established pursuant to Section 19521 from December 10 of the year in which the assessment should have been made to the date the assessment is added to the board roll;  provided, however, that no addition shall be made whenever the escape was due to an error, other than an erroneous opinion of value, on the part of the board.