Cal. Mil. & Vet. Code § 224
Rank: How Determined. All officers of the National Guard shall take rank according to the date assigned them by their commissions, which date shall be that of their appointment, except that in the case of an officer who has previously held the same or a higher grade in the California National Guard, California Air National Guard, the Officers' Reserve Corps, or has performed active duty in the same or a higher grade in the armed forces of the United States, his date of rank shall antedate his date of appointment by the length of time he has previously held such grade or performed such active duty. When two officers of the same grade are commissioned as of the same date, their rank shall be determined, first, by the length of previous services as an officer in the National Guard; second, by the length of previous military service in the National Guard; third, according to age, the eldest taking precedence.
Ca. Mil. and Vet. Code § 224