According to the
U.S. Census Bureau, the county has a total area of . Counties which border with Santa Clara County are, clockwise,
Alameda County,
San Joaquin (within a few hundred feet at
Mount Boardman),
Stanislaus,
Merced,
San Benito,
Santa Cruz, and
San Mateo County. Santa Clara County formerly shared borders with
Contra Costa,
San Francisco,
Mariposa,
Monterey, and
Tuolumne counties until 1853, 1856, 1874, and 1854 respectively (Monterey County currently comes within a few miles of Santa Clara). The
San Andreas Fault runs along the
Santa Cruz Mountains in the south and west of the county.
National protected area •
Don Edwards San Francisco Bay National Wildlife Refuge (part)
Fauna just north of U. S. Highway 101 in Basking Ridge Park. The freeway is a barrier to elk migration to the
Coast Range. Both
tule elk (
Cervus canadensis nannodes) and
pronghorn (
Antilocapra americana) were historically
native to Santa Clara County. In June 1776, Lieutenant Commander Don
José Joaquín Moraga led a group of soldiers and colonists from the Presidio of Monterey to establish
Mission San Francisco de Asis and encountered both tule elk and pronghorn, and clearly distinguished these two species from deer. The deer in California being
California mule deer (
Odocoileus hemionus). Regarding elk, Moraga wrote: "In the great plain called San Bernardino (the
Santa Clara Valley which stretches from south San Jose to
Gilroy), while the expedition was strung out at length, we descried in the distance a herd of large animals that looked like cattle, but we could not imagine where they belonged or from whence they had come...with horns similar in shape to those of the deer, but so large that they measured sixteen palms from tip to tip." Upon measurement, Morago reported the elk horns as four varas [] across... "These animals [elk] are called
ciervos in order to differentiate them from the ordinary Spanish variety of deer, here called
venados, which also exist in abundance and of large size in the vicinity."
General John Bidwell, of the 1841
Bartleson-Bidwell Party wrote: "In some of the fertile valleys, such as Napa and Santa Clara, there were elk literally by the thousand." 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. While other ranchers refused, tech pioneers
Bill Hewlett and
David Packard allowed Coletto and state biologists to translocate the initial 32 tule elk from the
Owens Valley in the eastern
Sierra onto the
San Felipe Ranch, which the families jointly own, in the hills east of
Morgan Hill. From the three original 1978–1981 translocations (totaling 65 animals) 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 such as the
Sunol and
Cottonwood Creek (near
San Luis Reservoir in western
Merced County, California) herds. , an estimated 400 tule elk roam in northeastern Santa Clara County and southeastern
Alameda County. In March 2014
CDFW translocated nine bull elk from the
San Luis National Wildlife Refuge to add genetic diversity to the San Antonio Valley Ecological Reserve herd in
San Antonio Valley in extreme eastern Santa Clara County. As of 2017 there were four herds in the Coyote Ridge area, often visible from U. S. Highway 101, according to Craige Edgerton, recently retired executive director of the Silicon Valley Land Conservancy and local naturalist Michael Hundt. In 2019, a fifth herd of tule elk was documented by local naturalist Roger Castillo, likely having split from the Coyote Ridge herd and established itself in Silver Creek Valley around the closed Ranch Golf Club. The elk herds in eastern Santa Clara County are blocked from dispersal to the west by U.S. Highway 101, with environmentalists advocating re-purposing the Metcalf Road bridge at the Coyote Gap into a wildlife overcrossing. The animals left the San Felipe Ranch for the
Isabel and
San Antonio Valleys, as well as an area near
Lake Del Valle in
Alameda County may now be extirpated by poaching, highway vehicle collisions, and insufficient numbers to defend pronghorn fawns against coyote predation. As of 2012, the Isabel Valley Ranch herd had dwindled to 3 animals, and the Lake del Valle herd to 13. Currently, iNaturalist.org has zero observer records of pronghorn in Santa Clara County.
The Nature Conservancy "Mount Hamilton Project" has acquired or put under conservation easement of land towards its goal for habitat conservation within a 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
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. As of 1980, Santa Clara County had the highest number of
Superfund Sites of any county in the United States, accounting for 25 polluted locations requiring a long-term response to clean up hazardous material contaminations. , Santa Clara County has 23 active Superfund Sites, still more than any other county in the United States. The vast majority of these Superfund sites were caused by firms associated with the high tech sector in
Silicon Valley. More recently, extensive
droughts in California, further complicated by drainage of the Anderson reservoir within the county for seismic repairs, have strained the county's
water security. ==Demographics==