Cal. Mil. & Vet. Code § 143

Whenever the Governor is satisfied that rebellion, insurrection, tumult or riot exists in any part of the state or that the execution of civil or criminal process has been forcibly resisted by bodies of persons, or that any conspiracy or combination exists to resist by force the execution of process, or that the officers of any county or city are unable or have failed for any reason to enforce the laws, the Governor may, by proclamation, declare any part of the State of California or the county or city or any portion thereof to be in a state of insurrection, and he or she may thereupon order into the service of the state any number and description of the active militia, or unorganized militia, as he or she deems necessary, to serve for a term and under the command of any officer as he or she directs.