Cal. Streets and Highways Code § 5832.8

(a) The board of supervisors may adopt an ordinance proposing the imposition of a special tax for the purpose of maintaining improvements. Such ordinance shall be submitted to the voters of the maintenance district and shall take effect upon approval of two-thirds of the voters of the district voting on the ordinance. The approval of the voters may be secured at a district or countywide election, or by a ballot mailed to each registered voter in the district. The election shall be conducted pursuant to the provisions of the Elections Code. (b) The ordinance submitted to the voters for approval pursuant to the provisions of subdivision (a) shall specify the terms of the special tax to be imposed which shall include the manner in which the obligation of each taxpayer is determined, when the special tax is to be levied, and the method of collection. The ordinance may also specify that the special tax imposed by the ordinance may be adjusted annually by the percentage change in the total appropriations subject to limitation of the local government for purposes of Article XIII B of the California Constitution. (c) Upon approval of the voters under subdivision (a), the board may levy the special tax as authorized by the ordinance, until superseded by a new ordinance adopted pursuant to the provisions of subdivision (a), or until repealed pursuant to an ordinance adopted by the board. (d) The provisions of this section shall apply only to maintenance districts located wholly within the Town of Portola Valley.