| Mount Umunhum | |
|---|---|
 Mount Umunhum from the southwest | |
| Highest point | |
| Elevation | 3,489 ft (1,063 m) NAVD 88[1] |
| Prominence | 586 ft (179 m)[1] |
| Coordinates | 37°09′38″N121°53′55″W / 37.1605016°N 121.8985666°W /37.1605016; -121.8985666[2] |
| Geography | |
  Mount Umunhum Location in California | |
| Location | Santa Clara County,California,United States |
| Parent range | Santa Cruz Mountains |
| Topo map | USGS Los Gatos |
| Geology | |
| Rock age | Oligocene |
| Climbing | |
| Easiest route | Mount Umunhum Rd |
Mount Umunhum (/ˈʌmənʌm/UH-mə-num) is a peak in theSanta Cruz Mountains, located inSanta Clara County,California. It is the fourth-highestpeak in the Santa Cruz Mountains, afterLoma Prieta,Crystal Peak, andMount Chual. Most of the mountain is located within theSierra Azul Open Space Preserve.
Mount Umunhum consists of ageologic formation that is known as theCoast Range Ophiolite. Thisophiolite is a piece of MiddleJurassicoceanic crust andmantle that has beenobducted onto land and largely been converted toserpentinite. It has been extensivelyfaulted anddiapiricallyuplifted anderoded to form Mt. Umunhum and extensiveoutcrop 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.[3][4]
Mount Umunhum and nearbyLoma Prieta are pushed upward by local collision forces associated with a left bend in theSan Andreas Fault. Starting nearUvas 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 archetypalrestraining bend which acts to opposestrike-slip motion along the fault.[5] From the perspective of Mount Umunhum and other mountains atop theSierra Azul block, thePacific Plate is trying to shear them off theNorth American Plate but can't break them off. Rather, the resultingtranspression force pushes up the local terrain and helps explain why these are the highest peaks in theSanta Cruz Mountains.[6]
Mount Umunhum is fromOhlone and means "Resting Place of the Hummingbird".[7]
The Cube, aradar tower which housed an 85.5-tonAN/FPS-24 radar, was completed in 1962 and used to watch for hostile aircraft during theCold War. Its signal caused electronic interference in many radio, TV and sound systems within its 250-mile range on each rotation.[8]
The summit was closed to the public due to hazardous materials and unsafe conditions caused by partially demolished structures from the formerAir Force station. Plans were made to clean it up and restore it for public use.[9][10] "In 2009, with federal funding,Midpeninsula Regional Open Space District removed 3,000 cubic yards of hazardous materials, includinglead paint,asbestos, fuel storage containers andPCB transformers; anddeconstructed 13,680 tons of concrete, asphalt, wood and other materials."[11] Despite these measures access to the summit area surrounding the cube was closed again in 2018 pending additional cleanup.[12] The demolition of the cube was considered, but in May 2016, theSanta Clara County Board of Supervisors listed it on the County Heritage Resource Inventory, giving it official historic status and protecting it from demolition.[13] On September 18, 2017, the road, amountain biking andhiking trail to the summit were opened. Facilities include new pavement, restrooms, interpretive displays and a small parking lot at the summit.[14] It is a spur of theBay Area Ridge Trail.[15]
In 2017, theMidpeninsula Regional Open Space District granted aneasement to theAmah Mutsun [Wikidata] tribal band, descendants of theOhlone Native American people who inhabited the region before it was settled by Europeans.[16] The easement authorized the band to build a garden and hold ceremonies on the mountaintop.[16]
In March 2022, the $2 million renovation project to preserve the historical building was completed.[17]
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".[18] The tower was part of Almaden Air Force Station, a radarsurveillance post which operated from 1958 to 1980.[19]
The mountain is also the site of the Bay AreaNEXRADweather radar.[20] 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.
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