Cal. Pub. Util. Code § 90773

The petition may include one or more separate documents, but each document shall contain the affidavit of the party who circulated it, certifying that each name signed thereto is the true signature of the person whose name it purports to be. The secretary of the district shall compare the signatures on the petition with the affidavits of registration on file with the county elections official and if he or she finds that the petition has been signed by the required number of voters he or she shall attach his or her signature thereto and present the petition to the board.