Cal. Pub. Util. Code § 130401

A retail transactions and use tax ordinance applicable in the incorporated and unincorporated territory of the county may be adopted by the commission in accordance with Section 130410 and Part 1.6 (commencing with Section 7251) of Division 2 of the Revenue and Taxation Code, if two-thirds of the electors voting on the measure vote to approve its imposition at a special election called for that purpose by the commission and an expenditure plan is adopted pursuant to Section 130406.