The Santa Teresa Hills are a range of mountains in

Santa Clara County Santa Clara County, officially the County of Santa Clara, is the sixth-most populous county in the U.S. state of California, with a population of 1,936,259, as of the 2020 United States Census, 2020 census. Santa Clara County and neighboring Sa ...

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

, located primarily in the city of San Jose. They separate the San Jose neighborhoods of

Almaden Valley , other_name= , native_name= es, Almadén , nickname= , settlement_type= Neighborhood of San Jose , total_type= , motto= , image_skyline = , flag_size= , image_sea= , seal_size= , image_shield= , shield_size= , image_blank_emblem= , ...

to the west and Santa Teresa to the east.

Geography

The range runs south of San Jose and is about 7 miles long. The

New Almaden , settlement_type = Neighborhood of San Jose , nickname = , motto = , image_skyline = , image_flag = , image_seal = , image_map = , mapsize = , map_caption = , image_map1 = , mapsize1 = , map_caption1 = , pushpin_map = United States Sa ...

hills and greater

Santa Cruz Mountains The Santa Cruz Mountains, part of the Pacific Coast Ranges, are a mountain range in central and Northern California, United States. They form a ridge down the San Francisco Peninsula, south of San Francisco. They separate the Pacific Ocean from ...

span south. Notable peaks include Coyote Peak and Bernal Hill. Notable bodies of water include Santa Teresa Creek, which runs west down through the southern portion of the hills. It soon joins Arroyo Calero, which originates from

Calero Reservoir Calero Reservoir, also called Calero Lake, is a reservoir in San Jose, California, located in the Calero neighborhood of Almaden Valley in South San Jose. It is the site of Calero County Park, which also includes a large area covering the lake a ...

in New Almaden. Arroyo Calero then joins Alamitos Creek, which flows through Almaden Lake at the western end of the Santa Teresa Hills, exiting eventually to the Guadalupe River and then to the

San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water from a ...

at Alviso. Santa Teresa Spring emerges at the base of the north side of the hills.

Geology

Serpentinized

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

rock from the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

, and

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

from the lower

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

, and

Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

Franciscan Complex The Franciscan Complex or Franciscan Assemblage is a geologic term for a late Mesozoic terrane of heterogeneous rocks found throughout the California Coast Ranges, and particularly on the San Francisco Peninsula. It was named by geologist Andrew ...

rock containing

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

and

basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

volcanic rock make up most of the geologic structure of the Santa Teresa Hills. The hills contain local

thrust faults A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

, while the Shannon Fault Zone cuts south.

Mining

Like in the nearby historic New Almaden mines, mining occurred in the Santa Teresa Hills since the early 20th century, though with much lower consistency and production. Limestone was quarried since 1915 for use in fertilizer and sugar refining, and chert was quarried for local road metal. Sandstone was quarried from 1866 to 1906 and was used in the construction of

Stanford University Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is consider ...

and several public buildings in

San Francisco San Francisco (; Spanish language, Spanish for "Francis of Assisi, Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the List of Ca ...

and San Jose. Rocks quarried here were also decoratively desirable. Past mines include the Bernal Mine, which has been inactive since 1918, and the Santa Teresa Mine, both of which were quicksilver mines. Like New Almaden, the Santa Teresa Hills contain “hilos,” or small tension fractures in silicate-carbonate rock containing veins of

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

, and

cinnabar Cinnabar (), or cinnabarite (), from the grc, κιννάβαρι (), is the bright scarlet to brick-red form of Mercury sulfide, mercury(II) sulfide (HgS). It is the most common source ore for refining mercury (element), elemental mercury and ...

, though in much lower quantity.

Cultural History

Don Bruno Bernal (Rancho Santa Teresa en S

Ancestors of today's Muwekma

Ohlone The Ohlone, formerly known as Costanoans (from Spanish meaning 'coast dweller'), are a Native American people of the Northern California coast. When Spanish explorers and missionaries arrived in the late 18th century, the Ohlone inhabited the ...

Tribe were among the first people to live in the Santa Teresa Hills area, with one major settlement at Santa Teresa Spring about 3000 years ago.Ford, Lawrence D. (October 12, 2011)
"Grazing Management Plan Santa Teresa County Park, San Jose, California"
(PDF). County of Santa Clara Department of Parks and Recreation. Retrieved 2022-09-30. The spring was a reliable freshwater source and a sacred site to the Muwekma Ohlone, who believe that the spring had healing properties.

Rancho Santa Teresa

In 1826, José Joaquín Bernal, a former soldier in the Mexican Army, settled near Santa Teresa Spring with his family and established Rancho Santa Teresa. The Santa Teresa Hills were part of the San Jose Pueblo Tract II, between Rancho Santa Teresa to the north and Alamitos Creek at the southern base. Rancho Santa Teresa started off as a 9,647 acre land grant by the Mexican government in 1834. Due the

California Land Act of 1851 The California Land Act of 1851 (), enacted following the Treaty of Guadalupe Hidalgo and the admission of California as a state in 1850, established a three-member Public Land Commission to determine the validity of prior Spanish and Mexican lan ...

, the rancho was reduced to only 400 acres by the 1870s. Bernal's descendants continued to run the ranch, which produced cattle, fruit and hay. The Bernal Mine, Bernal Marl Fertilizer Company, and Santa Teresa Spring Water Company were also started by Bernal's descendants. The ranch eventually became Bernal-Gulnac-Joice Ranch, and was operated into the 1980s. Mount Umunhum viewed from Santa Teresa County Park, July 2015

Mount Umunhum viewed from Santa Teresa County Park, July 2015

By the 1990s, a large portion of the Santa Teresa Hills were purchased by

as part of

Santa Teresa County Park Santa Teresa County Park is an park in the Santa Teresa, San Jose, Santa Teresa neighborhood of San Jose, California, located within the Santa Teresa Hills Park description It is operated by the Santa Clara County Parks and Recreation Departme ...

, which now covers about 1,688 acres. Today, a ranch house and other historic buildings remain at the base of the hills as part of the park. The

IBM Almaden Research Center IBM Research is the research and development division for IBM, an American multinational information technology company headquartered in Armonk, New York, with operations in over 170 countries. IBM Research is the largest industrial research org ...

, which opened in 1986, is located just west of the park.Cassidy, Mike (February 3, 2011)
"Cassidy: IBM's big influence on Silicon Valley"
''The Mercury News''
Archived
from the original on 2022-08-13. Retrieved 2022-10-14.

Ecology

The Santa Teresa Hills contain

chaparral Chaparral ( ) is a shrubland plant community and geographical feature found primarily in the U.S. state of California, in southern Oregon, and in the northern portion of the Baja California Peninsula in Mexico. It is shaped by a Mediterranean c ...

, annual grassland, mixed oak woodland, and mixed

riparian forests A riparian forest or riparian woodland is a forested or wooded area of land adjacent to a body of water such as a river, stream, pond, lake, marshland, estuary, canal, sink or reservoir. Etymology The term riparian comes from the Latin word ' ...

."Endangered and Threatened Wildlife and Plants; Designation of Critical Habitat for the Bay Checkerspot Butterfly (Euphydryas editha bayensis)"
(PDF). ''Federal Register''. U.S. Fish and Wildlife Service, U.S. Department of the Interior. 73 (166): 50406, 50426. August 26, 2008. Retrieved 2022-09-28. In areas that are less serpentine, non-native annual Eurasian grasses, including wild oats, soft chess, and

Italian ryegrass ''Lolium multiflorum'' (Italian rye-grass, annual ryegrass) is a ryegrass native to temperate Europe, though its precise native range is unknown. It is a herbaceous annual, biennial, or perennial grass that is grown for silage, and as a cover ...

, dominate over native grasses and forbs.

Serpentine soils Serpentine soil is an uncommon soil type produced by weathered ultramafic rock such as peridotite and its metamorphic derivatives such as serpentinite. More precisely, serpentine soil contains minerals of the serpentine subgroup, especially anti ...

are incredibly poor in essential plant nutrients like

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

and have high concentrations of

heavy metals upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...

. As such, the serpentine composition found in the Santa Teresa Hills provides an essential habitat for native plants that can tolerate these conditions from competition with non-native grasses. Native butchgrasses include California oatgrass, purple needlegrass, and

Idaho fescue ''Festuca idahoensis'' is a species of grass known by the common names Idaho fescue and blue bunchgrass. It is native to western North America, where it is widespread and common. It can be found in many ecosystems, from shady forests to open plai ...

. Native forbs include

filaree ''Erodium'' is a genus of flowering plants in the botanical family Geraniaceae. The genus includes about 60 species, native to North Africa, Indomalaya, the Middle East, and Australia. They are perennials, annuals, or subshrubs, with five-petal ...

, true clovers, and dwarf plantain. Mixed oak woodland species include

Coast live oak ''Quercus agrifolia'', the California live oak, or coast live oak, is a highly variable, often evergreen oak tree, a type of live oak, native to the California Floristic Province. It may be shrubby, depending on age and growing location, but is ...

, valley oak,

California buckeye ''Aesculus californica'', commonly known as the California buckeye or California horse-chestnut, is a species of buckeye native to California and southwestern Oregon. Description It is a large deciduous shrub or small tree, up to tall, with ...

California bay ''Umbellularia californica'' is a large hardwood tree native to coastal forests and the Sierra foothills of California, and to coastal forests extending into Oregon. It is endemic to the California Floristic Province. It is the sole species in th ...

, and blue oak. The Santa Teresa Hills are a critical habitat for the threatened

Bay checkerspot butterfly The Bay checkerspot (''Euphydryas editha bayensis'') is a butterfly endemic to the San Francisco Bay region of the U.S. state of California. It is a federally threatened species, as a subspecies of '' Euphydryas editha''. Since the 1980s the p ...

, who's primary host plant is the dwarf plantain. Other animals include

deer Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reindeer ...

coyotes The coyote (''Canis latrans'') is a species of canis, canine native to North America. It is smaller than its close relative, the wolf, and slightly smaller than the closely related eastern wolf and red wolf. It fills much of the same ecologica ...

bobcats The bobcat (''Lynx rufus''), also known as the red lynx, is a medium-sized cat native to North America. It ranges from southern Canada through most of the contiguous United States to Oaxaca in Mexico. It is listed as Least Concern on the IUC ...

wild turkeys The wild turkey (''Meleagris gallopavo'') is an upland ground bird native to North America, one of two extant species of turkey and the heaviest member of the order Galliformes. It is the ancestor to the domestic turkey, which was originally de ...

California quail The California quail (''Callipepla californica''), also known as the California valley quail or Valley quail, is a small ground-dwelling bird in the New World quail family. These birds have a curving crest or '' plume'', made of six feathers, tha ...

, red-shouldered hawks,

turkey vultures The turkey vulture (''Cathartes aura'') is the most widespread of the New World vultures. One of three species in the genus ''Cathartes'' of the family Cathartidae, the turkey vulture ranges from southern Canada to the southernmost tip of South ...

, and

rattlesnakes Rattlesnakes are venomous snakes that form the genera '' Crotalus'' and '' Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small an ...

References

{{Authority control Mountain ranges of Santa Clara County, California Santa Cruz Mountains Geography of San Jose, California Hills of California Mountain ranges of Northern California