Mount Hamilton (California)

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 named 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.[10] 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),[11] they named it Mt. Isabel.[12]

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 get 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.

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 38.1 inches (97 cm) in February 2019.[13] 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.[14]

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).[21] 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.

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.[22]

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).

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.[23][24]

Mount Hamilton has its own zip code, 95140. It is generally open space with a population in 2000 of 35.[25] Mount Hamilton Elementary is a small one classroom school (closed in 2006).[26]

• List of highest points in California by county
• List of summits of the San Francisco Bay Area
• Grant Ranch Park

Wikimedia Commons has media related to: Mount Hamilton (California)

• "Copernicus Peak". SummitPost.org. Retrieved 2011-05-07.
• "Mount Hamilton". The Nature Conservancy. Archived from the original on 2011-06-15. Retrieved 2011-05-08.
• "Visiting Lick Observatory". University of California Observatories. Retrieved 2011-05-08.
• "Old Hills, New Economies – A Natural History of the Mount Hamilton Ridgelands". BayNature. Retrieved 2011-05-08.
• Silicon Valley Land Conservancy