California Code, Streets and Highways Code - SHC § 8317

(a) Proof of publication of a notice shall be made by affidavit pursuant to the Code of Civil Procedure. Proof of the posting of a notice shall be made by affidavit of the person posting it, reciting the facts of the posting.

(b) An officer required to have any notice published or posted shall file the affidavit in his or her office. Failure to do so does not invalidate proceedings under this part. An affidavit so filed is prima facie evidence of the facts stated in it.