Cal. Welf. and Inst. Code § 870
Two or more counties may, pursuant to Article 1 (commencing with Section 6500) of Chapter 5 of Division 7 of Title 1 of the Government Code, establish and operate a joint juvenile hall. A joint juvenile hall shall be under the management and control of the probation officers of the participating counties, acting jointly, or of one of such probation officers, as provided by the agreement among the counties, and shall be in the charge of a superintendent selected pursuant to a civil service or merit system. A joint juvenile hall shall be operated in the manner prescribed by this chapter for juvenile halls.
A county participating in the maintenance of a joint juvenile hall pursuant to this section need not maintain a separate juvenile hall.
Ca. Welf. and Inst. Code § 870