California Code, Government Code - GOV § 8634

During a local emergency the governing body of a political subdivision, or officials designated thereby, may promulgate orders and regulations necessary to provide for the protection of life and property, including orders or regulations imposing a curfew within designated boundaries where necessary to preserve the public order and safety.  Such orders and regulations and amendments and rescissions thereof shall be in writing and shall be given widespread publicity and notice.

The authorization granted by this chapter to impose a curfew shall not be construed as restricting in any manner the existing authority of counties and cities and any city and county to impose pursuant to the police power a curfew for any other lawful purpose.