CA Gov't Code Section 26292.1

A retail transactions and use tax ordinance applicable in the incorporated and unincorporated territory of the county may be adopted by the agency in accordance with Section 26292.5 and Part 1.6 (commencing with Section 7251) of Division 2 of the Revenue and Taxation Code, if the ordinance is adopted by a two-thirds vote of the board of directors of the agency and 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 agency. The tax ordinance shall take effect at the close of the polls on the day of the election at which the proposition is adopted. The initial collection of the transactions and use tax shall take place in accordance with Section 26292.4.