Cal. Rev. & Tax. Code § 1605

(a) An assessment made outside of the regular assessment period is not effective for any purpose, including its review, equalization and adjustment by the county board, until the assessee has been notified thereof personally or by United States mail at the assessee’s address as contained in the official records of the county assessor. For purposes of this subdivision, for counties in which the board of supervisors has adopted the provisions of subdivision (c) and the County of Los Angeles, receipt by the assessee of a tax bill based on that assessment shall suffice as the notice.
(b) Upon application for reduction in assessment pursuant to subdivision (a) of Section 1603, the assessment shall be subject to review, equalization, and adjustment by the county board. In the case of an assessment made pursuant to Article 2 (commencing with Section 75.10) of Chapter 3.5 of Part 0.5, or Article 3 (commencing with Section 501) of Chapter 3 of Part 2 that is made outside the regular assessment period as defined in subdivision (f), or an assessment made pursuant to Article 4 (commencing with Section 531) of Chapter 3 of Part 2, the application shall be filed with the clerk in accordance with the applicable of the following:
1. (1) In a county other than the County of Los Angeles or a county in which the board of supervisors has adopted a resolution in accordance with subdivision (c), no later than 60 days after the date of mailing printed on the notice of assessment, or the postmark therefor, whichever is later. If the taxpayer does not receive the notice of assessment described in Section 75.31 or 534 at least 15 calendar days prior to the deadline established in the foregoing sentence, the party affected, or his or her agent, may file the application within 60 days of the date of mailing printed on the tax bill or the postmark therefor, whichever is later, along with an affidavit declaring under penalty of perjury that the notice of assessment was not timely received.
2. (2) In the County of Los Angeles or any county in which the board of supervisors has adopted a resolution in accordance with subdivision (c), an application subject to this subdivision shall be filed within the period specified in that subdivision.
(c) The board of supervisors of any county may by resolution require that the application for reduction pursuant to subdivision (a) of Section 1603 be filed with the clerk no later than 60 days after the date of mailing printed on the tax bill or the postmark therefor, whichever is later.
(d) In counties where assessment appeals boards have not been created and are not in existence, at any regular meeting, the board of supervisors, on the request of the assessor or any taxpayer, shall sit as the county board to equalize any assessments made by the assessor outside the regular assessment period for those assessments. Notwithstanding any other provision of law to the contrary, in any county in which assessment appeals boards have been created and are in existence, the time for equalization of assessments made outside the regular assessment period for those assessments, including assessments made pursuant to Sections 501, 503, 504, 531, and 531.5, shall be prescribed by rules adopted by the board of supervisors.
(e) If an audit of the books and records of any profession, trade, or business pursuant to Section 469 discloses property subject to an escaped assessment for any year, then the original assessment of all property of the assessee at the location of the profession, trade, or business for that year shall be subject to review, equalization and adjustment by the county board of equalization or assessment appeals board pursuant to this chapter, except in those instances when that property had previously been equalized for the year in question by the county board of equalization or assessment appeals board. The application shall be filed with the clerk no later than 60 days after the date on which the assessee was notified. Receipt by the assessee of a tax bill based upon that assessment shall suffice as that notice.
(f) For purposes of subdivision (a), “regular assessment period” means January 1 to and including July 1 of the calendar year in which the assessment, other than escape assessments, should have been enrolled if it had been timely made.