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Mount Hamilton is a mountain in Californiamarker's Diablo Rangemarker. In 1861, while working for Josiah D. Whitney on the first California Geological Survey, William H. Brewer invited local San Josemarker preacher (and Brewer's personal friend) Laurentine Hamilton to join his company on a trek to a nearby summit. Nearing completion of their journey, Hamilton, in good humor, bounded for the summit ahead of the rest of the men and claimed his stake. In fact, Brewer suggested the mountain be named after Hamilton only after Whitney declined to have the mountain named after him (a different mountain was later named Mount Whitneymarker).

Mount Hamilton is the tallest mountain overlooking Silicon Valleymarker, and is the site of Lick Observatorymarker, the first permanently occupied mountain-top observatory. The various summits along its mile-long summit ridge have been given astronomy-related names. The highest is Copernicus Peak at 4360+ feet (1329+ m). Kepler Peak and Observatory Peak follow. The latter was more than taller before it was leveled during the construction of the observatory in the 1880s. The asteroid 452 Hamiltonia, discovered in 1899, is named after the mountain. Golden Eagle nesting sites are found on the slopes of Mount Hamilton.


These mountains are high enough to receive snowfall in the winter, perhaps up to a dozen times. Occasionally, when a cold, wet storm comes in from the Gulf of Alaskamarker or Canadamarker, Mt. Hamilton and the surrounding peaks get serious snowfall. In February 2001, of snow fell, and in March 2006, the peak was left with over a foot (30 cm) of snow in one night.

The National Weather Service has had a cooperative weather station on the summit of Mount Hamilton almost since the time that the Lick Observatory opened. It has provided a glimpse of the extreme weather conditions that occur on the Diablo Range, especially in the winter months.

Hamilton had a foot of snow on the ground on April 1, 1967 (Robert E.

January is usually the coldest month on Mount Hamilton with an average high of and an average low of . The warmest month is usually July with an average high of and an average low of . Due to frequent thermal inversions during the summer, it is often warmer on Mount Hamilton than in San Jose. The record high temperature of was on August 5, 1978. The record low temperature of was on December 21, 1990. The average days with highs of or higher is 4.3 days. The average days with lows of or lower is 50.6 days.

Annual precipitation averages . Measurable rainfall occurs on an average of 71.9 days each year. The most rainfall in a month was in February 1998; no rainfall has been common during the summer months. The maximum rainfall in 24 hours was on December 23, 1955.

Annual snowfall averages . The maximum snowfall in a year was in 1955. The maximum snowfall in a month was in January 1950. The 24-hour maximum snowfall of occurred on February 18, 1990. The deepest daily snow depth was in March 1976. Measurable snow has been recorded in every month from November through June.

Mount Hamilton Road

State Route 130 begins its ascent from the junction at Alum Rock Road.

The sinuous Mt. Hamilton Road (part of State Route 130) is popular with bicyclists and motorcyclists. Built in 1875–76 in anticipation of the observatory, and the need to carry materials and equipment up the mountain in horse-drawn wagons, the grade seldom exceeds 6.5 percent. The road rises over in three long climbs from San Jose to the mountain top. Cyclists fondness for the road relate to the long but not overly challenging nature of the climb, sparse vehicular traffic over most of its length, and spectacular views of San Jose and the rest of the Santa Clara Valley below. There is an annual cycling challenge climb in April.Thanksgiving consistently draws hundreds of cyclists and is frequently the final climb in the annual Low-Key Hillclimb Serieswhich attracts some of the region's best climbers.

Strong regional climbers can attain the peak in 70–80 minutes starting from Alum Rock Road. On a clear day at the summit it is possible to see the Sierra Nevada. These views do not come without a price, as numerous accidents occur on the road each year. Whenever it snows on Mount Hamilton, the road is closed until crews can clear the road of snow and black ice.

The drive from Interstate 680 to Lick Observatory takes about 45 minutes.

The bicycle ride is just over from the Alum Rock Road junction. The upward trek is interrupted by two descents, first into Grant Ranch County Park, and again to cross Smith Creek. Quimby Road offers a shorter way from San Jose to Grant Ranch, but is considerably steeper. The main observatory building has water, a few vending machines, restrooms, and an opportunity to warm up on a cold day. If the time is right, there are also free 15-minute guided tours of the Great Lick refracting telescopemarker, and the gift shop may be open.

Hamilton Road is popular with the local cycling clubs.

The road is advertised to include 365 curves, one for each day of the year. This is true, subject to definition of the term "curve." If the yellow line bends to the right, then straightens out, then bends to the right again, it is regarded as one curve. If the yellow line describes an ess, on the other hand, it counts as two curves, regardless of how gentle the ess may be.

The road continues, as the San Antonio Valley Road, down the backside of Mount. Hamilton, through almost completely empty country, and eventually comes out at Pattersonmarker, in Stanislaus County. Shortly after the summit, one can turn to the north and proceed on Old Mines Road, which ends at Livermoremarker. There are ranches, farms, several cattle gates along this road, and even a (paved) ford through a shallow stream. Traffic is light to nonexistent.

Geology and hydrology

Much of the foothill slopes of Mount Hamilton is underlain by Miocene age sandstone of the Briones formation: this bedrock is locally soft and weathered in the upper few feet, but grades locally to very hard at depth. Depth to groundwater on these foothill areas of Mount Hamilton is approximately . The Babb Creek drainage comprises some of the watershed draining the slopes of Mount Hamilton. The Calaveras and Hayward active earthquake faults traverse the slopes of Mount Hamilton.

The community

Mount Hamilton has its own zip code, 95140; it is generally uninhabited open space with a population in 2000 of only 35. The place also has its own police force (one officer, a member of the University of California police), but because there were not enough school-age children in 2006, the Mount Hamilton Elementary School has been closed.

See also


  1. The Building of Lick Observatory
  2. 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.
  3. ZIP Code 95140 Census Data
  4. Mount Hamilton Elementary School, currently no enrollment

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