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The Diablo Range is a mountain range in western Californiamarker, part of the California Coast Ranges subdivision of the much larger Pacific Coast Ranges. According to the USGS, it extends from the Carquinez Straitmarker in the north to Orchard Peak in the south, near the point where State Route 46 crosses over the Coast Ranges at Cholamemarker. It is bordered on the northeast by the San Joaquin River, on the southeast by the San Joaquin Valleymarker, on the southwest by the Salinas River, and on the northwest by the Santa Clara Valley. The USGS designation is somewhat ambiguous north of the Santa Clara Valley, but on their maps, the range is shown as the ridgeline which runs between its namesake Mount Diablomarker southeastward to Mount Hamilton. Geologically, the range corresponds to the Coast Ranges east of the Calaveras Fault in this northern section.

A peak rising over 2,300 ft is considered high. The following peaks and ridges are between 2,517 and 5,241 ft and are distinct and summited often. They include Mission Ridgemarker (2,517-2,644 ft), Mount Diablomarker (3,889 ft), San Benito Mountainmarker (5,241 ft), Mount Hamilton Ridgemarker (4,230-4,260 ft), and Mount Stakesmarker (3,804 ft).

The range passes through Contra Costamarker, Alamedamarker, San Joaquin, Santa Claramarker, Stanislausmarker, Mercedmarker, San Benitomarker, Fresnomarker, Montereymarker, and Kingsmarker counties, and ends in the northwesternmost extremity of Kern Countymarker.

Major routes of travel through the range include State Route 4 (north of the range), I-580, State Route 152, State Route 198, and State Route 46/State Route 41 (south of the range). Important passes include Altamont Passmarker, Pacheco Passmarker, and Polonio Pass. It is paralleled for much of its distance by U.S. Route 101 to the west and by I-5 to the east. A sparsely used gravel road is the highest road in the range, with its highest point being San Benito Mountain at 5,200 feet (1,585 m).

The Diablo Range is largely unpopulated, particularly outside of the San Francisco Bay Areamarker. Major nearby communities include Antiochmarker, Concordmarker, Walnut Creekmarker, Pleasantonmarker, Livermoremarker, Fremontmarker and the Central Valley city of Tracymarker. In the South Bay, communities near (though not in) the range are Milpitasmarker, eastern San Josemarker, Morgan Hillmarker, and Gilroymarker. South of Pacheco Pass, the only major nearby communities (those with a population over 15,000) are Los BaƱosmarker, and Hollistermarker. The small town of Coalingamarker may also be notable for its location on State Route 198, one of the few routes through the mountains.

Most of the range consists of private ranchland, limiting recreational use. However, the range does contain several areas of parkland, including Mount Diablo State Parkmarker, Alum Rock Park, Grant Ranch Park, Henry W.marker Coe State Parkmarker, and the BLM's Clear Creek Management Area. The East Bay Regional Park District in Contra Costa and Alameda counties is the largest urban park holder in the country, with places like Mission Peak Regional Preservemarker and the interconnected Sunol Regional Wilderness, Ohlone Wildernessmarker and Del Valle Regional Parkmarker; these parks form a huge swath of wildland in Alameda County.

Environmental aspects

The Diablo Range generally has a chaparral and California oak woodland environment, with stands of alpine conifers appearing above 4,000 feet (1,219 m). Gray pines and Coulter pines can be found at all elevations, though, especially between 800 and 3000 ft. Coulter pine reaches its northern limit north of Mt. Diablo. Since the range lies around 10 to 50 miles (16 to 80 km) inland from the ocean, and other coastal ranges like the Santa Lucia Rangemarker and the Santa Cruz Mountainsmarker block incoming moisture, the range gets little precipitation. In addition, the average elevation of 3,000 to 4,000 feet (915 to 1,219 m) is not high enough to catch most of the incoming moisture at higher altitudes. Winters are mild with moderate rainfall, but summers are very dry and hot. Areas above 2,500 feet (762 m) get light to moderate snow in the winter, especially at the highest point, the 5,241 ft (1,597 m) San Benito Mountainmarker in the remote southeastern section of the range. However, though sites at the lower end get annual snowfall, it is typically light and melts too fast to be noticed. Once or twice a decade there is seriously deep and long lasting snowfall. Golden Eagle nesting sites are found in the Diablo Range, reaching their highest density in southern Alameda County. The Diablo Range attracts far more raptors than coastal forests. Black-tailed deer are abundant, and Tule Elk live in small, disjunct populations from Santa Clara to Contra Costa counties. They are slowly recovering. Pronghorn, grizzly bears, and quite likely wolves have been extirpated. There still are numerous coyotes and some of the better mountain lion populations in the state. There are excellent populations of bobcats and gray foxes, who depend on the chaparral. The Northern Pacific Rattlesnake lives in good numbers. There are many ground squirrels, hares, and various species of rodents, native and nonnative. The bunchgrass understory is long gone, except in a few rare fragments. The understory is dominated with nonnative invasives. The most common trees are coast live oak and blue oak; the largest blue oak grows in Alameda County. There are also good populations of buckeye, and even California black oak. The conifers are pretty much limited to common gray and rarer coulter pines, with some knobcone pines.

Some streams draining the eastern slopes of the Diablo Range include Hospital Creek and Ingram Creek.


  1. C. Michael Hogan, Paul Hoffey et al. al., Environmental Impact Report for the Aiassa Site off Mount Hamilton Road, Santa Clara County, Ca., Santa Clara County Document EMI 7364W1 SCH88071916, August, 1989
  2. Peterson, Hans- Raptors of California

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