Cal. Pub. Util. Code § 50500

If the district operates no transit facilities, or its exterior boundaries become coincident with the boundaries of a single city, the board may call an election at any time for the purpose of submitting to the voters of the district the question of whether the district will be dissolved. Upon the filing with the secretary of the district of a petition signed by voters within the district equal in number to at least 25 percent of the total vote cast at the last general statewide election, asking that the question of dissolution of the district be submitted to the voters of the district, the board shall call such an election.