Cal. Rev. & Tax. Code § 7286.90
(a) In addition to the tax levied pursuant to Part 1.5 (commencing with Section 7200) and any other tax authorized by this part, the Board of Supervisors of the County of San Mateo may impose a transactions and use tax in lieu of, and not in addition to, a tax imposed under Section 7285.5 for the purposes described in paragraph (4), by the adoption of an ordinance in accordance with this part if all of the following conditions are met: