Cal. Mil. & Vet. Code § 233

An officer who desires to resign shall submit his or her resignation to the Governor, whose action thereon shall be final. The Governor may refuse to accept a resignation when the officer is under investigation, under charges, awaiting the result of a trial, absent without leave, absent in the hands of civil authorities, in default with respect to state or federal funds or property, mobilized for deployment on state or federal duty, or notified of impending mobilization for state or federal military duty.