CA Rev & Tax Code Section 759

(a)

If a timely petition for reassessment is not filed in accordance with the notice provided by the board pursuant to Section 758, an escape assessment or roll correction shall become final at the expiration of the period for filing a petition for reassessment specified by that notice.

(b)

The board may extend the period for filing a petition for reassessment once for a period not to exceed 15 days, provided a written request for the extension is filed with the board prior to the expiration of the period for which the extension may be granted.