California Code, Vehicle Code - VEH § 2812

Whenever poisonous gas, explosives, dust, smoke, or other similar substances, or fire exist upon or so near a public highway as to create a menace to public health or safety, members of the California Highway Patrol, police departments, or sheriff's office may close any highway to traffic when necessary to protect the public from such dangers. Whenever a highway is closed, the governmental agency having control over the highway shall be immediately notified of the reason of the closing and the location.