Mount Umunhum


Length 7.7 mi · Climbing 1130 ft
California > San Francisco Bay Area

The Mount Umunhum radar tower

Topped with its distinctive blocky radar tower, Mount Umunhum is one of the most recognizable landmarks in the South Bay. The peak was long off limits, but after a major cleanup operation removed almost all of an abandoned air force station, it was opened to the public in 2017. You now have a choice of driving or hiking to the top.

The hike uses a new purpose-built singletrack trail that switchbacks up to the summit. The trail runs through somewhat patchy woods mixed with scrub. You get a few brief glimpses of the surrounding landscape, but no really sweeping views until the very end. The trail is also longer than it needs to be because it has an average grade of only 5.4%, only half as steep, for example, as the ultra-popular Mission Peak. So the climb is a little monotonous, especially the long series of switchbacks near the top, but reaching the summit makes it worthwhile.

The trail is surprisingly popular given that it’s kind of remote, and that you can just drive to the summit, which is by far the best part of the hike. At peak times you might see a group about every 5 minutes on the trail.

Hike description

Click map to show all roads and trails
Part of the Almaden Valley trail map from Redwood Hikes Press (digital download for mobile devices)

Here’s the trailhead location in Google Maps.

Start from the Bald Mountain parking lot, halfway up Mount Umunhum Road. The lot only has 25 parking spots, and it can be difficult to find parking on weekends. The trail starts across the road and a little uphill from the parking lot.

The trail immediately enters the woods and begins a steady climb. There are mileage markers to help you keep track of your progress, but they seem to be a little too closely spaced; after the 3.0 mile marker it’s still a long way to the peak.

Much of the Mount Umunhum Trail is wooded

The most significant landmark along the way is the Guadalupe Creek Overlook, a short side trail to a viewing area with a somewhat restricted view of the Santa Clara Valley. The overlook also marks the beginning of the switchbacks.

As it nears the peak, the trail breaks out of the woods for good. After climbing a flight of stone stairs, the trail curves around the peak, offering the best views so far. But it’s not until you finally reach the peak that the most dramatic views open up.

The trail breaks out of the woods and makes its final climb to the peak

A paved trail loops around an oddly barren, rocky hill near the radar tower. There’s no vegetation here yet beacuse this area was once bulldozed flat, and the park created the rocky hill to restore the original topography of the peak.

Descend to the summit parking lot by way of a long flight of stairs, then cross the road and pick up the trail where it begins next to a small picnic area. From here, descend the same way that you came.

Sierra Azul Open Space Preserve and the Santa Clara Valley as seen from the peak

The Bald Mountain Trail (1.4 mi)

Just across from the start of the Mount Umunhum Trail is the Bald Mountain Trail, which in some ways is actually more enjoyable. The mostly level dirt road winds through attractive open grasslands with views of the rugged green mountains, climbing slightly to a sweeping view of the vast Santa Clara Valley and the Coyote Valley. Together, the Mount Umunhum and Bald Mountain Trails make about a 9-mile hike.

The Bald Mountain Trail

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© 2017, 2022 David Baselt