California Code, Health and Safety Code - HSC § 7355

(a) Except as provided in subdivision (b), the bodies of persons who have died from any cause shall not be received for transportation by a common carrier unless the body has been embalmed and prepared by a licensed embalmer and placed in a sound casket and enclosed in a transportation case.

(b) A dead body, which cannot be embalmed or is in a state of decomposition, shall be received for transportation by a common carrier if the body is placed in an airtight metal casket enclosed in a strong transportation case or in a sound casket enclosed in an airtight metal or metal-lined transportation case.