916.12—District.
District means the applicable one of the following described subdivisions of the production area or such other subdivision as may be prescribed pursuant to § 916.31 :
(c)
District 3 shall include all of the production area lying south of the northern boundaries of the counties of San Luis Obispo, Kern, and San Bernardino.
(d)
District 4 shall include the counties of Merced, Stanislaus, and the balance of the production area.