Cal. Gov. Code § 25351.5
When a county owns, leases or operates a convention hall, an exhibition hall, an auditorium, an opera house, a music hall and center, a museum, an art gallery, or an amphitheater as a place of public assembly for the use, benefit and enjoyment of the public, the board of supervisors may by ordinance levy an admission tax on the base purchase price of tickets sold for admission to any such facility. "Base purchase price" means the amount which is actually paid, and not the regular established price, for admission to the facility, exclusive of all other taxes, federal, state, or city, which are now or may hereafter be imposed on such admission. No tax shall be due in the case of a person admitted free of charge.
The ordinance shall provide for the administration and collection of the tax. The proceeds of the tax shall be deposited in the county treasury to be expended for the maintenance and operation of the facility from which the proceeds are derived. The amount of the tax shall not exceed 10 percent of the base purchase price of admission charged and shall not in any event exceed the amount necessary to defray the annual maintenance and operation expense of the facility from which the proceeds are derived.
Ca. Gov. Code § 25351.5