Cal. Pub. Util. Code § 101285

Whenever any petition signed by voters within the district equal in number to at least 15 percent of the total vote cast within the district at the last general statewide 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 for the cost thereof, the secretary of the district shall forthwith transmit the petition to the county elections official for certification.