California Code, Revenue and Taxation Code - RTC § 7284

(a) The board of supervisors of any county may license, for revenue and regulation, and fix the license tax upon, every kind of lawful business transacted in the unincorporated area of the county, including shows, exhibitions, and games. The board may provide for collection of the license tax by suit or otherwise.

(b) Any board which imposes a license tax pursuant to subdivision (a) upon a business operating both within and outside the board's taxing jurisdiction shall levy the tax so that the measure of tax fairly reflects that proportion of the taxed activity actually carried on within the taxing jurisdiction.