Cal. Gov. Code § 58907
No proceeding shall be held invalid for omission of the clerk of the supervising body to mail the notice required by this chapter to any property owner unless such owner objects to such omission within 30 days after the public hearing or initial action with reference to which such notice was omitted. No objection shall be considered unless it is made in writing, signed, under oath by such owner or his duly authorized representative, and filed with the clerk of the supervising authority. Upon the expiration of said 30 days, the clerk may file an affidavit stating whether or not any property owner entitled to a mailed notice under this chapter who has not been mailed such notice, has filed the objection herein authorized. The affidavit of the clerk shall be conclusive evidence as to the filing or nonfiling of objections within the period of 30 days as above required. If a valid objection is filed within the time allowed, the supervising authority shall conduct another hearing or reconsider its initial action on the proposal, after complying with the notice provisions of this chapter and the principal act under which the proposal was initiated. The time allowed by such principal act for the taking of any proceedings subsequent to the initial action or hearing shall be extended for such additional time as may be required to comply with this chapter.
Ca. Gov. Code § 58907