Cal. Rev. & Tax. Code § 7286.59

(a) In addition to the tax levied pursuant to Part 1.5 (commencing with Section 7200), and any other tax authorized by this part, a board of supervisors of a county may impose a transactions and use tax in lieu of, and not in addition to, a tax imposed under Section 7285.5 for the purposes described in paragraph (4), by the adoption of an ordinance in accordance with this part if each of the following conditions are met:
1. (1) The ordinance imposing the tax is submitted to and approved by the voters of the county by a two-thirds vote of those voters voting on the ordinance in accordance with Article 3.7 (commencing with Section 53720) of Chapter 4 of Part 1 of Division 2 of Title 5 of the Government Code.
2. (2) The ordinance includes an expenditure plan describing the specific purposes for which the revenues from the tax may be expended.
3. (3) The tax is imposed at a rate of 0.125 or 0.25 percent for a period not to exceed 16 years.
4. (4) The revenues collected from the tax are used only for funding public library construction, acquisition, programs, and operations within the county. These revenues shall be used only to supplement existing expenditures for public libraries and shall not be used to supplant existing funding for the support of public libraries.
5. (5) The transactions and use tax conforms to Part 1.6 (commencing with Section 7251).
(b) “Public library” means a library, or two or more libraries that are operated as a single entity by one or more public jurisdictions, that serve the general public and are required to report appropriations to the State Librarian under the provisions of Section 18023 of the Education Code.
(c) The board of supervisors may impose a transactions and use tax in any succeeding period not to exceed 16 years per period if all of the conditions specified in subdivision (a) are met for that succeeding period.