Mount Umunhum ( ) is a peak in the

Santa Cruz Mountains The Santa Cruz Mountains ( Mutsun Ohlone: Mak-sah-re-jah, "Sharp Ridged Mountain of the Eagle" or "People of the Eagle Mountain") are a mountain range in central and Northern California, United States, constituting a part of the Pacific Coast R ...

, located 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 census. Santa Clara County and neighboring San Benito County form the ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. It is the fourth-highest

peak Peak or The Peak may refer to: Basic meanings Geology * Mountain peak ** Pyramidal peak, a mountaintop that has been sculpted by erosion to form a point Mathematics * Peak hour or rush hour, in traffic congestion * Peak (geometry), an (''n''-3)-d ...

in the Santa Cruz Mountains, after Loma Prieta, Crystal Peak, and Mount Chual. Most of the mountain is located within the Sierra Azul Open Space Preserve.

Geology

Mount Umunhum consists of a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

that is known as the '' Coast Range Ophiolite.'' This

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle (Earth), upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is ...

is a piece of Middle

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 143.1 Mya. ...

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramaf ...

and mantle that has been obducted onto land and largely been converted to

serpentinite Serpentinite is a metamorphic rock composed predominantly of serpentine group minerals formed by serpentinization of mafic or ultramafic rocks. The ancient origin of the name is uncertain; it may be from the similarity of its texture or color ...

. It has been extensively faulted and

diapir A diapir (; , ) is a type of intrusion in which a more mobile and ductilely deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–Taylor ...

ically uplifted and

eroded Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. Erosion is disti ...

to form Mt. Umunhum and extensive

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

areas throughout the Santa Cruz Mountain foothills and elsewhere. The Coast Range Ophiolite is also known to underlie the rocks of the Great Valley throughout central California. The exposure on the northeast face of Mt. Umunhum is one of the best Bay Area exposures of the Coast Range Ophiolite.Bailey, E. H., Blake Jr, M. C., and Jones, D. L. (1970). ''On-land Mesozoic oceanic crust in California coast ranges.''
US Geological Survey Professional Paper
', 700, C70-C81.Stoffer, P. W. and Messina, P. (2002)
''Field-Trip Guide to the Southeastern Foothills of the Santa Cruz Mountains In Santa Clara County, California.''
''US Geological Survey Open-File Report'', 2, p. 121. Mount Umunhum and nearby Loma Prieta are pushed upward by local collision forces associated with a left bend in the

San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...

. Starting near Uvas Canyon, the fault stops trending northwest but instead bends west-northwest for about eight miles before continuing its northwest direction. This left bend is renowned among geologists as an archetypal restraining bend which acts to oppose

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

motion along the fault. From the perspective of Mount Umunhum and other mountains atop the Sierra Azul block, the Pacific Plate is trying to shear them off the North American Plate but can't break them off. Rather, the resulting

transpression In geology, transpression is a type of Strike-slip fault, strike-slip deformation that deviates from simple shear because of a simultaneous component of shortening perpendicular to the fault plane. This movement ends up resulting in oblique shear. ...

force pushes up the local terrain and helps explain why these are the highest peaks in the

History

Mount Umunhum is from

Ohlone The Ohlone ( ), formerly known as Costanoans (from Spanish meaning 'coast dweller'), are a Native Americans in the United States, Native American people of the Northern California coast. When Spanish explorers and missionaries arrived in the l ...

and means "Resting Place of the Hummingbird". The Cube, a

radar tower A radar tower is a tower whose function is to support a radar facility, usually a local airport surveillance radar, and hence often at or in the vicinity of an airport or a military air base. The antenna is often continually rotating. In additio ...

which housed an 85.5-ton AN/FPS-24 radar, was completed in 1962 and used to watch for hostile aircraft during the

Cold War The Cold War was a period of global Geopolitics, geopolitical rivalry between the United States (US) and the Soviet Union (USSR) and their respective allies, the capitalist Western Bloc and communist Eastern Bloc, which lasted from 1947 unt ...

. Its signal caused electronic interference in many radio, TV and sound systems within its 250-mile range on each rotation. The summit was closed to the public due to hazardous materials and unsafe conditions caused by partially demolished structures from the former

Air Force An air force in the broadest sense is the national military branch that primarily conducts aerial warfare. More specifically, it is the branch of a nation's armed services that is responsible for aerial warfare as distinct from an army aviati ...

station. Plans were made to clean it up and restore it for public use. "In 2009, with federal funding, Midpeninsula Regional Open Space District removed 3,000 cubic yards of hazardous materials, including

lead paint Lead paint or lead-based paint is paint containing lead. As pigment, lead(II) chromate (, "chrome yellow"), lead(II,IV) oxide, (, "red lead"), and lead(II) carbonate (, "white lead") are the most common forms.. Lead is added to paint to acceler ...

asbestos Asbestos ( ) is a group of naturally occurring, Toxicity, toxic, carcinogenic and fibrous silicate minerals. There are six types, all of which are composed of long and thin fibrous Crystal habit, crystals, each fibre (particulate with length su ...

, fuel storage containers and PCB transformers; and

deconstructed Deconstruction is a philosophical theory. Deconstruction or Deconstructed may also refer to: Music Albums * ''Deconstructed'' (Bush album), a 1997 compilation album * ''Deconstructed'' (EP), an EP by Kesha * ''Deconstructed'' (Steve Swallow a ...

13,680 tons of concrete, asphalt, wood and other materials." Despite these measures access to the summit area surrounding the cube was closed again in 2018 pending additional cleanup. The demolition of the cube was considered, but in May 2016, the

Board of Supervisors listed it on the County Heritage Resource Inventory, giving it official historic status and protecting it from demolition. On September 18, 2017, the road, a

mountain biking Mountain biking (MTB) is a sport of riding bicycles off-road, often over rough terrain, usually using specially designed mountain bikes. Mountain bikes share similarities with other bikes but incorporate features designed to enhance durability ...

and

hiking A hike is a long, vigorous walk, usually on trails or footpaths in the countryside. Walking for pleasure developed in Europe during the eighteenth century. Long hikes as part of a religious pilgrimage have existed for a much longer time. "Hi ...

trail to the summit were opened. Facilities include new pavement, restrooms, interpretive displays and a small parking lot at the summit. It is a spur of the

Bay Area Ridge Trail The Bay Area Ridge Trail (shortened as Ridge Trail) is a multi-use trail along the hill and mountain ridgelines surrounding the San Francisco Bay Area, in Northern California. It is planned to extend ; , have been established. When complete, ...

. In 2017, the Midpeninsula Regional Open Space District granted an

easement An easement is a Nonpossessory interest in land, nonpossessory right to use or enter onto the real property of another without possessing it. It is "best typified in the right of way which one landowner, A, may enjoy over the land of another, B" ...

to the tribal band, descendants of the

Native American people who inhabited the region before it was settled by Europeans. The easement authorized the band to build a garden and hold ceremonies on the mountaintop. In March 2022, the $2 million renovation project to preserve the historical building was completed.

Facilities

The mountain is topped by an eight and a half story (84.5 feet tall) concrete radar tower (5 floors interior), known locally as "the Cube" or "the Box". The tower was part of Almaden Air Force Station, a radar

surveillance Surveillance is the monitoring of behavior, many activities, or information for the purpose of information gathering, influencing, managing, or directing. This can include observation from a distance by means of electronic equipment, such as ...

post which operated from 1958 to 1980. The mountain is also the site of the Bay Area

NEXRAD NEXRAD or Nexrad (Next-Generation Radar) is a network of 159 high-resolution S-band pulse-Doppler radar, Doppler weather radars operated by the National Weather Service (NWS), an agency of the National Oceanic and Atmospheric Administration (NOAA) ...

weather radar A weather radar, also called weather surveillance radar (WSR) and Doppler weather radar, is a type of radar used to locate precipitation (meteorology), precipitation, calculate its motion, and estimate its type (rain, snow, hail etc.). Modern w ...

. The high elevation is necessary for line of sight in the region's varied terrain, but it also limits the ability to detect storms with bases lower in the atmosphere.

Gallery

Image:P3030017MtUmunhumSnow crwb.jpg, Mount Umunhum is occasionally dusted with snow File:Umunhum2017.jpg, Aerial view from the north File:Mount Umunhum aerial with Monterey Bay.jpg, Aerial view with Monterey Bay in background File:View of radar tower on Mount Umunhum.jpg, The abandoned radar tower and parking lot in 2020 File:Mount Umunhum Cube from close up.jpg, The abandoned radar tower in 2020 File:Radar tower Mount Umunhum April 2022 3.jpg, The radar tower and parking lot in 2022 after renovation File:Radar tower Mount Umunhum April 2022 2.jpg, The radar tower in 2022 File:Mount Umunhum - NEXRAD Weather Radar.jpg, NEXRAD weather radar File:Mount Umunhum - West from Mount Umunhum Rd.jpg, Mount Umunhum, looking west from Mount Umunhum Rd File:Mount Umunhum from Bald Mountain.jpg, Mount Umunhum as seen from Bald Mountain

References

External links

* * 10m, 18s. * * * * {{DEFAULTSORT:Umunhum, Mount Mountains of Santa Clara County, California Mountains of the San Francisco Bay Area Santa Cruz Mountains Mountains of Northern California