CA Pub Util Code Section 131102

(a)

A retail transactions and use tax ordinance for a tax of either one-half of 1 percent or 1 percent applicable in the incorporated and unincorporated territory of a county may be imposed by a county transportation authority or the commission in the manner prescribed in Section 131103 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 an election which shall be called for this purpose by the board of supervisors within one year after the adoption of a county transportation expenditure plan. (b)The ordinance shall take effect at the close of the polls on the day of election at which the proposition, as set forth in Section 131108, is adopted. The ordinance shall specify the period, as determined by the adopted county transportation expenditure plan during which the tax will be imposed. The tax may be terminated earlier if the projects in the adopted plan are completed and any bonds outstanding issued pursuant to this division are redeemed.