Cal. Water Code § 75881

The failure of any person interested in the district, or in the matter of the proposed change of its boundaries, to show cause in writing why the proposed change of boundaries of the district should not be made shall be deemed and taken as an assent by him to the change of the boundaries of the district as prayed for in the petition for the inclusion of lands, or to such a change of such boundaries as will include a part of the lands; and the filing of such petition shall be deemed and taken as an assent on the part of each petitioner to such a change of the boundaries as may include the whole or any portion of the lands described in the petition.