Cal. PUC § 60100

A retail transactions and use tax ordinance applicable in the incorporated and unincorporated territory of the county may be imposed by the district in accordance with this chapter and Part 1.6 (commencing with Section 7251) of Division 2 of the Revenue and Taxation Code, if the tax ordinance is adopted by a majority of the board of directors and by a majority of the governing bodies of the appointing authorities listed in subdivision (a) of Section 60008, and imposition of the tax is subsequently approved by two-thirds of the voters voting on the measure at a special election called for that purpose by the board of supervisors, at the request of the district, and a county transportation expenditure plan is adopted pursuant to Section 60106.

A retail transactions and use tax approved by the voters shall remain in effect for not longer than 20 years, or any lesser period of time specified in the tax ordinance. The tax may be continued in effect, or reimposed, by a tax ordinance adopted by the district and the reimposition of the tax is approved by two-thirds of the voters.