Cal. Health & Safety Code § 13053

Whenever a fire occurs in any county or within the boundaries of any national forest which is of such proportions that it cannot be adequately handled by the forestry department or fire warden of the county or the facilities of the Department of Forestry and Fire Protection or of the United States Forest Service, the personnel, equipment, and firefighting facilities of any county may be authorized by the state forest ranger within the county or the county forester or fire warden of the county to assist in its extinguishment and control.