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Mount Hamilton (California) facts for kids

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Mount Hamilton
Sierra de Santa Isabel
IMG 9864MountHamilton fxwb.jpg
Lick Observatory is visible atop Mount Hamilton; hillsides show typical summer golden (dry) vegetation
Highest point
Elevation 4,265 ft (1,300 m) NAVD 88
Prominence 93 ft (30 m)
Mount Hamilton is located in California
Mount Hamilton
Mount Hamilton
Location in California
Location Santa Clara County, California, U.S.
Parent range Diablo Range
Topo map USGS Lick Observatory
Age of rock Upper Cretaceous
First ascent 1861
Easiest route Hike

Mount Hamilton is a mountain in the Diablo Range in Santa Clara County, California. The mountain's peak, at 4,265 feet (1,300 m), overlooks the heavily urbanized Santa Clara Valley and is the site of Lick Observatory, the world's first permanently occupied mountain-top observatory. The asteroid 452 Hamiltonia, discovered in 1899, is named after the mountain. Golden eagle nesting sites are found on the slopes of Mount Hamilton. On clear days, Mount Tamalpais, the Santa Cruz Mountains, Monterey Bay, the Monterey Peninsula, and even Yosemite National Park are visible from the summit of the mountain.


Hotel Santa Ysabel on Smith Creek 1895
Hotel Santa Ysabel on the road up Mt. Hamilton just across Smith Creek in 1895, Courtesy of San Jose Public Library, California Room

On August 26, 1861, while working for Josiah D. Whitney on the first California Geological Survey, William H. Brewer invited local San Jose 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 Whitney).

The Spanish name for Mt. Hamilton was the Sierra de Santa Isabel and the highest point was originally known as Mount Isabel instead of Mount Hamilton. William Henry Brewer and his fellow geologist, Charles F. Hoffmann, did not know it already had a name, and christened it Mt. Hamilton, although they did place Isabel Valley on their map to the east. The "Hotel Santa Ysabel" was built on the road up the mountain in 1885 on Smith Creek. When in 1895, the USGS realized that the peak two miles southeast of Mt. Hamilton was as tall (4,193 ft or 1,278 m), they named it Mt. Isabel.


P3040016MtHamiltonSnow crwb
Numerous times each winter temperatures drop low enough for Mount Hamilton (left) to receive as much as a foot of snow for a day or two.

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 Alaska or Canada, Mt. Hamilton and the surrounding peaks such as Mt Diablo receive significant snowfall. In February 2001, 30 inches (76 cm) of snow fell, and in March 2006, the peak was left with over a foot (30 cm) of snow in one night. Most of the time, though, the snow on Mt Hamilton rarely accumulates more than an inch and melts the next day.

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.

Mt. Hamilton had a foot of snow on the ground on April 1, 1967

January is usually the coldest month on Mount Hamilton with an average high of 49.4 °F (9.7 °C) and an average low of 37.5 °F (3.1 °C). The warmest month is usually July with an average high of 78.2 °F (25.7 °C) and an average low of 63.1 °F (17.3 °C). Due to frequent thermal inversions during the summer, it is often warmer on Mount Hamilton than in San Jose. The record high temperature of 103 °F (39 °C) was on August 5, 1978. The record low temperature of 7 °F (−14 °C) was on December 21, 1990. The average days with highs of 90 °F (32 °C) or higher is 4.3 days. The average days with lows of 32 °F (0 °C) or lower is 50.6 days.

Annual precipitation averages 23.73 inches (603 mm). Measurable rainfall occurs on an average of 71.9 days each year. The most rainfall in a month was 12.13 inches (308 mm) in February 1998; no rainfall has been common during the summer months. The maximum rainfall in 24 hours was 6.87 inches (174 mm) on December 23, 1955.

Annual snowfall averages 10 inches (25 cm). The maximum snowfall in a year was 59.0 inches (150 cm) in 1955. The maximum snowfall in a month was 33.6 inches (85 cm) in January 1950. The 24-hour maximum snowfall of 14.0 inches (36 cm) occurred on February 18, 1990. The deepest daily snow depth was 18 inches (46 cm) in March 1976. Measurable snow has been recorded in every month from November through June.

Climate data for Mount Hamilton, California (Station Elevation 4,206ft)
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Record high °F (°C) 73
Average high °F (°C) 48.5
Average low °F (°C) 36.8
Record low °F (°C) 10
Precipitation inches (mm) 4.43
Snowfall inches (cm) 5.0
Source: The Western Regional Climate Center


Copernicus Peak

Mount Hamilton is one summit along a mile-long ridge. Other than Hamilton, peaks along the ridge have astronomical names, such as Kepler. The highest peak on the ridge is Copernicus Peak, with elevation 4,360+ft (1,330+m). Copernicus Peak is located 0.8 miles (1.3 km) to the northeast from Mount Hamilton, and is highest point in Santa Clara County. Unlike Mount Hamilton's limited prominence, Copernicus Peak has a prominence of 3,080 ft (940 m).

Mount Hamilton Road

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

The sinuous 19-mile (31 km) 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 4,000 feet (1,200 m) in three long climbs from San Jose to the mountain top. On a clear day at the summit it is possible to see the Sierra Nevada.

Cyclists' fondness for the road relates 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 Series which attracts some of the region's best climbers.

Cyclists Above Grant Ranch
Cyclists drafting each other on the ascent in order to best their time to the top.

Strong regional climbers can attain the peak in 70–80 minutes starting from Alum Rock Road.

The 20-mile (32 km) drive from Interstate 680 to Lick Observatory takes about 45 minutes.

The bicycle ride is just over 19 miles (31 km) 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 telescope, and the gift shop may be open.

Mt hamilton road cyclist
Mt. Hamilton Road is popular with cycling clubs.

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 240 feet (73 m). 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.

Ecology and conservation

Tule Elk - Merced National Wildlife Refuge Bill Leikam 12-03-2010
Tule elk roam the Diablo Range and are often seen on Coyote Ridge

Several rare species can be seen on Mount Hamilton. The Mount Hamilton jewelflower (Streptanthus callistus) is endemic to the area. In June 2011, five juvenile California condors flew over Mt. Hamilton and landed on the Lick Observatory, the species' first sighting in the area in at least 30 years.

In 1978, California Department of Fish and Game warden Henry Coletto urged the department to choose the Mount Hamilton area as one of California's relocation sites under a new statewide effort to restore tule elk (Cervus canadensis ssp. nannodes). Tule elk were thought to have been extinct until a breeding pair was discovered in the San Joaquin Valley in 1874-1875. Although some ranchers opposed re-introduction of elk to Santa Clara County, tech pioneers Bill Hewlett and David Packard allowed Coletto and state biologists to translocate 32 tule elk from the Owens Valley in the eastern Sierra onto the 28,000-acre San Felipe Ranch, which the families jointly own, in the hills east of Morgan Hill. From the three original 1978-1981 translocations to the Mount Hamilton region of the Diablo Range, there are multiple herds in different locations, including the Isabel Valley, San Antonio Valley, Livermore area, San Felipe Ranch, Metcalf Canyon, Coyote Ridge, Anderson Lake, and surrounding areas. Currently an estimated 400 tule elk roam 1,875 square kilometres (724 sq mi) in northeastern Santa Clara County and southeastern Alameda County. A 1985 study showed that more than 50% of the tule elk diet were grasses. This is consistent with studies of Point Reyes National Seashore tule elk fecal material which documented that the tule elk preferred grasses and forbs with little use of shrubs such as willow.

Kluft photo Mt Hamilton Lick Observatory night Img 4606
Lick Observatory on Mount Hamilton at night. Timed exposure taken from Grant Ranch Park.

The Nature Conservancy "Mount Hamilton Project" has acquired or put under conservation easement 100,000 acres (400 km2) of land towards its 500,000 acres (2,000 km2) goal for habitat conservation within a 1,200,000 acres (4,900 km2) area encompassing much of eastern Santa Clara County as well as portions of southern Alameda County, western Merced and Stanislaus Counties, and northern San Benito County. Acquisitions to date include the 1,756-acre Rancho Cañada de Pala, straddling the Alameda Creek and Coyote Creek watersheds for California tiger salamander habitat; a conservation easement on the 3,259-acre Blue Oak Ranch Reserve, which abuts the north side of Joseph D. Grant County Park; a conservation easement on the 28,359-acre San Felipe Ranch, connecting Joseph D. Grant County Park with Henry W. Coe State Park; the 2,899-acre South Valley Ranch which protects a tule elk herd in the San Antonio Valley, and other properties.

The community

Mount Hamilton has its own zip code, 95140. It is generally open space with a population in 2000 of 35. Mount Hamilton Elementary is a small one classroom school (closed in 2006).

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