The District, as established by the Act, is subdivided into six zones with interests, responsibilities or geographical divisions distinctive of the particular zone. In matters of taxation or ventures, each zone functions independently although by mutual arrangements joint activities may be entered into. The total area the District covers is 20,105 sq. mi.
The six zones, although bounded by defined limits within the Act, are generally described as follows:
275 sq. mi.
The westerly portion of the San Bernardino Valley extending from Beech Avenue in the Fontana area to the Los Angeles County line, all south of the San Gabriel mountain range divide. This includes the Cities of Chino, Chino Hills, Fontana, Montclair, Ontario, Rancho Cucamonga and Upland with the community of Etiwanda.
318 sq. mi.
The central area of the San Bernardino Valley, easterly of Zone 1 to approximately the Santa Ana River and City Creek demarcations. This includes the Cities of Colton, Fontana, Grand Terrace, Highland, Loma Linda, Redlands, Rialto and San Bernardino with the communities of Bloomington, Del Rosa, Devore and Muscoy.
366 sq. mi.
The easterly end of the San Bernardino Valley, east of Zone 2 including the Cities of Highland, Loma Linda, Redlands, San Bernardino and Yucaipa with the community of Mentone.
1,783 sq. mi.
The Mojave River Valley from the San Bernardino Mountains to Silver Lakes. This includes the Cities/Towns of Adelanto, Apple Valley, Barstow, Hesperia and Victorville and all or portions of the communities of Baker, Baldy Mesa, Daggett, Desert Knolls, El Mirage, Helendale, Hinkley, Hodge, Lenwood, Oro Grande, Phelan, Pinon Hills, Silver Lakes, Spring Valley Lake, Wrightwood and Yermo.
163 sq. mi.
The mountainous watershed of the Mojave River on the crest and north slopes of the San Bernardino Mountains including the communities of Arrowbear Lake, Blue Jay, Cedar Glen, Crestline, Green Valley Lake, Lake Arrowhead, Lake Gregory, Rimforest, Running Springs, Silverwood Lake, Skyforest, Snow Valley and Twin Peaks.
17,200 sq. mi.
The remainder of the County not embraced by other zones including portions of the San Gabriel and San Bernardino Mountains and the semi-desert portion of the County. This includes the Cities/Towns of Big Bear, Needles, Yucca Valley and Twenty-nine Palms with the communities of Amboy, Joshua Tree, Lucerne Valley, Morongo Valley, Newberry Springs and Trona.