Mount Umunhum & The Tower of Doom, San Jose, CA

What is that ominous-looking cube on the mountain in South San Jose? Perched atop Mount Umunhum (pronounced: oom-un-hum), a mysterious concrete cube stands watch, overlooking Silicon Valley. If you’ve ever wondered about the “Tower of Doom” as we’ve been lovingly calling it, you’re not alone. Locals also refer to it as “the Cube” or “the Box”. But whatever you want to call it, we were determined to see what it was! After a little snooping around, we found the road that leads to the site, so we hopped in the car and ventured to the summit of Mount Umunhum to uncover its mysterious secret.

What to see once you’re on top of Mount Umunhum?

1) The Views from Mount Umunhum

From the summit, the world seems to unfold beneath you. On a clear day, the entire Bay Area stretches out like a patchwork quilt – cities, valleys, and ridgelines fading into the horizon.

Looking east, we easily spotted downtown San Jose’s skyline, with distant glimpses of Oakland, Mount Diablo, and even San Francisco shimmering far off in the haze. To the west, the Santa Cruz Mountains roll endlessly toward the coast, and if the weather’s right, you’ll catch the glint of the Pacific Ocean.

There’s something surreal about standing between a bustling metropolis and the raw, untamed beauty of the coast. It’s a view that lingers long after you’ve left.

Fun Facts

• Mount Umunhum (Santa Clara County): 3,486 feet
• Mount Hamilton (Santa Clara County): 4,265 feet—home to the Lick Observatory
• Mount Diablo (Contra Costa County): 3,848 feet
• Mount Tamalpais (Marin County): 2,579 feet

Weather permitting, you can see all of the other three peaks from Mount Umunhum. Not bad for a single vantage point! Next time we’ll remember the binoculars!

2) Native American History, Mount Umunhum

What does the name Mount Umunhum mean?

The name Umunhum carries a deep and spiritual meaning: “the resting place of the hummingbird.” For the Amah Mutsun (Ohlone) people, this mountain has long been a sacred site for creation, healing, and spiritual visions.

As you explore the summit, you’ll find a large ceremonial circle—a powerful reminder of the land’s enduring significance to the Amah Mutsun Tribal Band. The surrounding area is also home to over 150 plant species that hold cultural importance for the Ohlone people.

The ongoing preservation of this sacred space is a testament to the partnership with the Midpeninsula Regional Open Space District, which in 2017 granted a cultural conservation easement to support the Amah Mutsun in stewarding the mountaintop. This collaborative effort helps protect the mountain’s cultural and ecological integrity for generations to come.

3) Cold War History—Almaden Air Force Station

That mysterious concrete cube—the one we affectionately call the “Tower of Doom”—is actually a relic of the Cold War. From 1957 to 1980, this 85ft tall behemoth (without radar) served as the nerve center of the Almaden Air Force Station, one of 23 radar towers in California built to monitor for Soviet threats.

In its Cold War prime, the base supported a small on-site community of over 160 military personnel and their families. Despite the remote location, they enjoyed a sense of “normalcy” thanks to amenities like a general store, a swimming pool, and even a bowling alley!

The doors at the base of the Cube have been completely sealed off (yes, we checked 😊), but we couldn’t help imagining how perfect it would be as a small museum. Maybe a space to showcase Cold War operations, military life at the site, and a deeper history of the Ohlone people and their sacred land.

While there’s no museum yet, you’ll find a lovely shaded observation deck beside the Tower of Doom, complete with benches and educational plaques about the area. And yes, there are also well-maintained parking lots and restrooms.

4) Outdoor Adventures in the SF Bay Area

Mount Umunhum is just one part of the vast Sierra Azul Open Space Reserve, a 19,000-acre wonderland for outdoor enthusiasts. While we enjoyed the easy access to the summit, the area is crisscrossed with trails perfect for hiking, biking, horse riding, and birdwatching. 

During our visit, we spotted dozens of purple martins, the largest swallow in North America, flitting around the summit. While we weren’t lucky enough to spot any golden eagles, their presence in the area added a thrilling sense of anticipation… Besides the sites and birdwatching, this entire area is perfect for finding your own slice of tranquility or a new adventure to conquer.

Practicalities—Visiting Mount Umunhum

Ready to plan your trip to Mount Umunhum? Here’s everything you need to know for a smooth visit.

• Getting There: The summit is accessible by car. From San Jose, it’s about a 50-minute drive, though the last few miles on Mount Umunhum Road are winding and steep, so drive with caution. Note that the only public access is via Hicks Road to Mount Umunhum Road; some GPS directions may lead you to private, locked roads.
• Parking: Ample parking is available at the summit. The main lot is the Mount Umunhum Summit Parking Area. There are also a limited number of ADA-accessible parking spaces in a separate lot closer to the summit area.
• Access for All Abilities: The site is designed to be inclusive. There are ADA-accessible pathways at the summit that lead to key viewpoints, the ceremonial circle, and a shelter. This allows visitors of all abilities to experience the stunning 360-degree views.
• Summit Hikes: While you can drive directly to the summit, dedicated hikers can take the Mount Umunhum Trail, a 3.7-mile trail from the Bald Mountain parking area to the summit. This is a multi-use trail for hikers and bikers, though the final section at the very top is for hikers only.
• Hours: The preserve is open from 7 a.m. to a half-hour after sunset. It’s always a good idea to check the official Midpeninsula Regional Open Space District website for any last-minute closures due to weather or maintenance.
• What to Bring:
  • Water: There is no drinking water available at the summit, so bring plenty of your own, especially on warm days.
  • Layers: Even on a sunny day in the Bay Area, the summit can be windy and much colder.
  • Binoculars (recommended): To get the best view of distant landmarks and wildlife. There’s a lot to see from up there!

Dogs: Unfortunately, No dogs are allowed in the Mount Umunhum area, including on the trails, at the summit, in the parking lots, or even in cars on Mount Umunhum Road.

Ready to see the “Tower of Doom” for yourself? The drive up is scenic and manageable, and once you get there, the 360-degree views are worth every minute. For more outdoor adventures in the San Francisco Bay Area, check out our articles on Uvas Canyon Park, Alum Rock Park, or Foothills Park to start with. Any other places you’d recommend us to write about next? Let us know in the comments below, and subscribe to our blog!