California Code, Revenue and Taxation Code - RTC § 7286.31

(a) The board of supervisors of the County of San Diego, subject to the approval of the voters, may impose a tax rate of one-half of 1 percent under this chapter and Part 1.6 (commencing with Section 7251) of Division 2. Neither this chapter nor any ordinance or resolution approved pursuant to this chapter shall affect any tax otherwise authorized.

(b) The combined rate of tax imposed in the County of San Diego by any public entity pursuant to Part 1.5 (commencing with Section 7200) or Part 1.6 (commencing with Section 7251) of Division 2, this chapter, and any other provision of law authorizing the imposition of local sales or transactions and use taxes shall not exceed 2.25 percent.