Cal. Business and Professions Code § 715

Unless otherwise required by federal law or regulation, no board under this division which licenses dentists, physicians and surgeons, podiatrists, or nurses may require a person to obtain or maintain any license to practice a profession or render services in the State of California if one of the following applies: (a) The person practicing a profession or rendering services does so exclusively as an employee of a department, bureau, office, division, or similarly constituted agency of the federal government, and provides medical services exclusively on a federal reservation or at any facility wholly supported by and maintained by the United States government. (b) The person practicing a profession or rendering services does so solely pursuant to a contract with the federal government on a federal reservation or at any facility wholly supported and maintained by the United States government. (c) The person practicing a profession or rendering services does so pursuant to, or as a part of a program or project conducted or administered by a department, bureau, office, division, or similarly constituted agency of the federal government which by federal statute expressly exempts persons practicing a profession or rendering services as part of the program or project from state laws requiring licensure.