Cal. Elec. Code § 6584

Each section shall be prepared with the lines for signatures numbered, and shall have attached the affidavit of the circulator who obtained signatures to it, stating, under penalty of perjury, that all the signatures to the attached section were made in his or her presence, and that to the best of his or her knowledge and belief each signature to the section is the genuine signature of the person whose name it purports to be. No other affidavit is required.