Cal. Pub. Util. Code § 90603

Whenever any petition signed by voters within the district equal in number to at least 15 percent of the total vote cast at the last general election is presented to the board asking for the acquisition, construction, or completion of the whole or any portion of any transit facilities or for acquiring any works, lands, structures, rights, equipment, or other property necessary or convenient to carry out the objects, purposes, or powers of the district, and also asking that a bonded indebtedness be incurred to pay the cost thereof, the secretary of the district shall immediately examine and verify the signatures of the petition and certify the result of the examination to the board.