Cal. Public Resources Code § 9166

(a) Within 30 days after the date of filing a petition, the executive officer of the local agency formation commission shall cause the petition to be examined and shall prepare a certificate of sufficiency indicating whether the petition is signed by the requisite number of signers. (b) If the certificate of the executive officer shows the petition to be insufficient, the executive officer shall immediately give notice by certified mail of the insufficiency to the chief petitioners. That mailed notice shall state in what amount the petition is insufficient. Within 15 days after the date of the notice of insufficiency, the chief petitioners may file with the executive officer a supplemental petition bearing additional signatures. (c) Within 10 days after the date of filing a supplemental petition, the executive officer shall examine the supplemental petition and certify in writing the results of his or her examination. (d) The executive officer shall sign and date a certificate of sufficiency. That certificate shall also state the minimum signature requirements for a sufficient petition and show the results of the executive officer’s examination. The executive officer shall mail a copy of the certificate of sufficiency to the chief petitioners.