CAL. MVC. CODE § 550 : California Code - Section 550

Whenever any part of the National Guard of this State is in active federal service, or when Congress so consents thereto, the Governor is hereby authorized to organize and maintain within this State during such period, under such regulations as the Secretary of Defense of the United States may prescribe for discipline in training, such military forces as the Governor may deem necessary to defend and for the security of this State; provided, however, the Governor may authorize the organization and maintenance of such forces at cadre strength at any time. Such forces shall be composed of officers commissioned or assigned, and such qualified citizens or aliens who have declared their intentions to become citizens as shall volunteer for service therein, supplemented, if necessary, by members of the unorganized militia enrolled by draft or otherwise as provided by law. Such forces shall be additional to and distinct from the National Guard and shall be known as the State Military Reserve. Such forces shall be uniformed under such conditions and subject to such regulations as the Governor may prescribe.