Cal. Penal Code § 1480

The person upon whom the writ is served must state in his return, plainly and unequivocally: 1. Whether he has or has not the party in his custody, or under his power or restraint; 2. If he has the party in his custody or power, or under his restraint, he must state the authority and cause of such imprisonment or restraint; 3. If the party is detained by virtue of any writ, warrant, or other written authority, a copy thereof must be annexed to the return, and the original produced and exhibited to the Court or Judge on the hearing of such return; 4. If the person upon whom the writ is served had the party in his power or custody, or under his restraint, at any time prior or subsequent to the date of the writ of habeas corpus, but has transferred such custody or restraint to another, the return must state particularly to whom, at what time and place, for what cause, and by what authority such transfer took place; 5. The return must be signed by the person making the same, and, except when such person is a sworn public officer, and makes such return in his official capacity, it must be verified by his oath.