Cal. Rev. & Tax. Code § 4876

When it can be ascertained from any roll or from any papers of the board what was intended or what should have been assessed, defects in description or form or clerical errors of the board in assessing state-assessed property or other errors of the board not involving the exercise of judgment as to value which result in the entry on the roll of assessed values other than those intended by the board may be corrected by the board under this article at any time within four years after the assessment was made or within the period for which a waiver is given pursuant to Section 868.