Cal. Food & Agr. Code § 66528
"Districts" consist of:
District 1.(Blythe area) Riverside and San Bernardino Counties.
District 2.(Imperial Valley area) Imperial County.
District 3.(Oxnard-Santa Maria area) Los Angeles, Orange, San Diego, San Luis Obispo, Santa Barbara, and Ventura Counties.
District 4.(Salinas-Watsonville area) Monterey, San Benito, Santa Cruz, Santa Clara, San Mateo, San Francisco, Marin, Sonoma, Mendocino, Humboldt, Alameda, and Del Norte Counties.
District 5.(San Joaquin-Sacramento Valley area) Sacramento, Kern, Fresno, San Joaquin, Stanislaus, Tulare, King, Merced, Madera, Contra Costa, Yolo, Solano, Napa, Colusa, Sutter, Yuba, Glenn, Butte Counties, and all other counties of California not included in Districts 1, 2, 3, and 4.
The number of districts and the boundaries of any district may be changed by a two-thirds vote of the commission when necessary to maintain similar total production among the districts and to ensure proper representation of producers. District boundaries are not required to coincide with county boundaries.
Ca. Food and Agric. Code § 66528