Sentinel of Silicon Valley: The Radar Tower at Mount Umunhum is Saved

Sentinel over Silicon Valley. Photo: Courtesy of Jitze Couperus CC BY 2.0
Sentinel over Silicon Valley. Photo: Courtesy of Jitze Couperus

It was a clandestine military post, a mysterious mountain tower, and a secret control room filled with the blips and bleeps of sci fi-worthy technology. During the Cold War, the radar tower atop Mt. Umunhum embodied the stuff of Cold War fantasy. Besides guarding the Santa Clara Valley from Soviet bombers, the post was a catalyst for technological advances that paved the way for today’s Silicon Valley.

Yet after 22 years of protecting the valley, the long-decommissioned tower is now the subject of an impassioned debate about its future.

Radar Tower. Photo: Basim Jaber Photography
The boxy radar tower atop Mt. Umunhum. Photo: Basim Jaber Photography

How Silicon Valley Learned to Stop Worrying and Love Radar

By the end of World War II, the rivalry between the US and the Soviet Union had heated up enough to kick-start the Cold War. The Soviet Union detonated their first atomic bomb in 1949 and, as the former regime began annexing Eastern European countries, US officials began planning an expansive air defense system to secure the country’s perimeter. Until the advent of intercontinental ballistic missiles, the biggest threat to American shores was airborne, nuclear-armed bombers.

In 1958, Almaden Air Force Station was founded as an early warning site at Mt. Umunhum, the fourth-highest peak in the Santa Cruz Mountains. (If you think the Soviets didn’t have their eyes trained on the San Francisco Bay Area, take a peek at this fascinating Cold War era map.) Named for the Ohlone Indian word for “resting place of the hummingbird,” Mt. Umunhum became the site of a self-sustaining military community — complete with swimming pool and bowling alley — of 125 airmen and their families. At the center of the station, a spinning radar swept the skies for hostile aircraft.

Keeping watch at the radar tower, 1964. Photo: Basim Jaber Historic Archives
Keeping watch at the radar tower, 1964. Photo: Basim Jaber Historic Archives

This was not the first radar in the Santa Clara Valley. Stanford University, Moffett Field naval air station, and nearby defense-funded technology firms made the valley the home of numerous radar advances and military research in the early 20th century. In the 1930s, Stanford University initiated a pioneering research park and invited Varian Associates to be its first tenant so that it could build radar components for the military.

Ops Room,1960. Photo: Basim Jaber Historic Archives
Operations room, 1960. Photo: Basim Jaber Historic Archives

Yet when Almaden was opened, radars were still manual, isolated, and couldn’t offer the panoptic view that defense officials craved. Enter IBM’s Military Products Division. Eager to win a significant post-war military contract, the computing giant linked radars by designing the world’s first computer network, something that would herald the modern Internet.

SAGE-Topped Mountains

In 1961, The Almaden Air Force Station became part of an innovative nationwide network dubbed SAGE, for Semi-Automatic Ground Environment. Engineered by IBM, SAGE was a series of interconnected computers that captured info from radars around the nation to form one central picture of US airspace. This data was fed to the North American Aerospace Defense Command, known as NORAD, as information for a military response via jets or missiles from nearby bases.

Clouds over Mt. Umunhum. Scene from Santa Teresa County Park. Photo:Don DeBold CC BY 2.0
Clouds over Mt. Umunhum. Scene from Santa Teresa County Park. Photo: Don DeBold

SAGE had the distinction of being the largest, most expensive computer system ever built and the first online network of geographically distributed computers in the world. The station atop Mt. Umunhum was one node in a network of 24 SAGE “direction centers.” The central building in each center was a windowless blast-resistant concrete behemoth. Known simply as Building 102, the center at Mt. Umunhum was topped with a massive 85-ton radar “sail” that oscillated and covered a whopping 250-mile range. Local residents soon learned to live with a regular zip of interference on radios and television screens as byproducts of the radar that stood sentinel high above the valley.

SAGE Display Scope. Photo: Joi Ito CC BY 2.0
SAGE Display Scope. Photo: Joi Ito

The enormous SAGE computers filled a room and required a staff of 100 to operate. Airmen sat at round monochromatic screens, or display scopes, with pulsating lights that made Pong look cutting-edge. The SAGE computer system was captured in two time capsule-worthy films produced by IBM: A TV commercial that introduced the system to the public and “On Guard!,” a 12-minute short with a paternal narrator who reminded us that SAGE was on the job around the clock.

SAGE Computer History Museum. Photo:Steve JurvetsonCC BY 2.0
The real SAGE computer displayed at the Computer History Museum. This is a great museum in Mountain View. Click here for hours. Photo: Steve Jurvetson

At the Movies

SAGE didn’t just star in propaganda shorts. It made appearances in feature films, including the Cold War satire “Dr. Strangelove,” where it surrounds a frantic Peter Sellers trying to stave off nuclear Armageddon. The wheelchair-bound character of Dr. Stangelove was based on one of the architects of SAGE who was also principal member of the Manhattan Project, John von Neumann. As SAGE was dismantled, pieces were used as set props in movies such as “Lost in Space,” “Planet of the Apes,” and “War Games,” a sci fi flick that pits an unknowing hacker against a nuclear-ambitious supercomputer in Sunnyvale, California.

Open Space and the Fight for Preservation

As technologies advanced and satellites began to eclipse radars, the staff at Almaden dwindled and the station was ultimately shuttered in 1980. In 1986, it was sold to the Midpeninsula Regional Open Space District, or Midpen, a Bay Area land preservation agency. Midpen is in the process of restoring the land to its natural state so that the previously restricted property can be enjoyed by the public as an open space preserve. In 2011, KQED detailed the restoration project in an engaging 10-minute film. The new park is scheduled to open on October 22, 2016 with interpretive trails, natural and cultural history exhibits, and sweeping top-of-the-world views.

Mt. Umunhum From Almaden Lake in San Jose. Photo: Basim Jaber Photography
Mt. Umunhum from Almaden Lake in San Jose. Photo: Basim Jaber Photography

Given the time-worn disrepair to the radar structure and a lack of a background in historic preservation, Midpen announced plans to demolish the iconic tower, the last remaining structure on the former air force station. In 2014, the Santa Clara Valley unexpectedly lost a similar Cold War landmark, the boxy operations center used for tracking spy satellites from the former Onizuka Air Force Station in Sunnyvale — what locals called The Blue Cube. It was demolished in 2014.

The threat to the Almaden radar tower mobilized a group of individuals to form the Umunhum Conservancy to help save the structure. Midpen agreed to halt plans to raze the tower if the conservancy could raise $1.5 million by 2017. Basim Jaber, a founding director of the conservancy and de facto historian of Almaden AFS, is a strong advocate of the tower’s preservation. In advocating for the significance of saving the atomic age icon, Basim states, “Not only did air defense technology help shape Silicon Valley, it contributed to the blanket of protection that let this valley thrive to what it is today.” Jaber brings the Almaden Air Force station back to life in vividly detailed slideshows presented every other month. Held at the Quicksilver Mining Museum, in the shadow of Mt. Umunhum, the free demonstrations are buoyed by Jaber’s extensive collection of historical photos and archives. For a schedule of upcoming slideshows, check the conservancy’s website.

The effort to save the radar tower has recently made great strides. The Santa Clara County Board of Supervisors voted on May 10, 2016 to put it on the county’s Heritage Resource Inventory, a designation making it immune from demolition as long as the building is cared for and not falling down. The Umunhum Conservancy plans to take great care of it. As of May 2016, they have raised about $375,000 toward their $1.5 million goal.

Mt. Umunhum Sunset. Photo:Dawn Ellner CC BY 2.0
Mt. Umunhum sunset. Photo: Dawn Ellner

Be sure and check out this Cold War gem and the surrounding hiking trails when Midpen opens the area to the public. It was scheduled to open on October 22, 2016, but has been delayed to mid-next year due to construction delays and increased costs. When it does open, Basim Jaber has graciously offered to give Mobile Ranger fans a guided hiking tour after it opens. If you are interested, please say so in the comments section that follows.

Updated October 24th, 2016

  1. Sources

About The Author

Garrick Ramirez

Hi, I'm a writer and photographer based in San Francisco. As a California native, I have a passion for -- and encyclopedic knowledge of -- destinations throughout the state. I know its cities, weekend escapes, and trends. I indulge each of these things through my writing, photography and blog, Weekend del Sol.

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  1. Daniel Rich

    Great piece on the tower, but there I have one correction for you. “… The Blue Cube. It was demolished without warning under the cover of early morning darkness.” — that’s not really accurate, the demolition lasted for months. They started dismantling the building in Sept of 2013 and performed the final demolition over two days in April 2014. The final demolition was somewhat secretive more likely due to the secure nature of the site, not to avoid any preservation attempts.

  2. ASHIS poddar

    We live right below the mountains of alamaden and love take a guided tour.i would love to help the conservancy in some form or shape if possible.Whenever I drive home back from north, the tower gives a feeling of home-coming after a long tirng day 🙂 thanks to all who put great effort saving this landmark

  3. Tim McMurray

    Please add me to the list for the guided hiking tour. I can see the radar tower from my front yard.

  4. Glenn Thompson

    An interesting article that both brought back memories & provided some surprising new insight for me. Once, back in the 60s, as a teenager, I rode my motorcycle up the Mt. Umunhum road, on through the radar station, & on down the other side, ignoring the stern warnings not to do so. Interestingly enough for me, by 1965, I was being trained to maintain SAGE computers, then deployed to Sioux City Air Base, & finally to Hancock Field, before being discharged in Nov, 1968. I still have considerable SAGE training material saved from my military classes.
    One clarification I might make to the narrative: The passage that reads “The station atop Mt. Umunhum was one node in a network of 24 SAGE “direction centers.” is misleading. Almaden Air Force Station was a radar site, not a Direction Center, that fed radar data into a Direction Center, probably Hamilton Air Force Base. The figure of 24 DCs throughout the country sounds correct, although the number varied throughout the SAGE era. There were also a smaller number of or Combat Centers (CCs) to accompany the DCs. This early experience was pivotal to my ultimate career which revolved around IBM mainframe computers, as was the case with a good number of others trained on these systems.

  5. John Haskey

    “It was demolished without warning under the cover of early morning darkness”

    This statement is misleading. The demolition took place over many days and was visible to the surrounding area. At the time I was working in Sunnyvale and a co-worker took daily ‘progress’ photos of the demolition as it happened.


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