Cal. RTC § 7286.32

(a) A retail transactions and use tax ordinance applicable in the incorporated and unincorporated territory of the County of San Diego shall be adopted by the board of supervisors in accordance with Section 7286.31 and Part 1.6 (commencing with Section 7251) of Division 2, if the tax is approved by a two-thirds vote of the qualified voters of the county voting on the measure at a special election called for that purpose by the board. The election called by the board shall be held within the incorporated and unincorporated areas of the county. The tax ordinance shall take effect 48 hours subsequent to the closing time 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 7286.35.

(b) Notwithstanding Section 7286.38 and subdivision (a) of this section, in the event voters approve a constitutional amendment permitting the imposition of a local special tax with the approval of a majority of the voters voting on the measure, the vote requirement for approval of the tax authorized by this act shall be a majority of voters voting on the measure.