Alto Bowl Open Space Preserve,
Marin County Open Space District,
Marin County
In brief:
2.2 mile out and back hike through preserves bordering Mill Valley residential neighborhoods.

Distance, category, and difficulty:
This 2.2 mile out and back hike is easy, with about 250 feet in elevation change. Trailhead elevation is about 330 feet. The hike dips to about 170 feet, then climbs back to about 350 feet. On the return, you'll face the same, in reverse. There is one steep stretch. You can use this trailhead as a staging area for long and more challenging Mount Tam hikes (via Camino Alto Open Space Preserve), but there are other trailheads with more parking and easier access to the heart of Tam.

Mostly exposed.

Trail traffic

Trail surfaces
Dirt trails and fire roads and one short sidewalk segment.

Hiking time
1 hour.

Good anytime, although often muddy in winter and early spring.

Getting there:
From US 101 in Marin County, exit East Blithedale/Tiburon Boulevard. Drive west on East Blithedale about 0.8 mile, then turn right onto Camino Alto. Drive north on Camino Alto about 1.2 miles, to a pullout on the right side, about 120 feet from an open space gate on the right.

Get driving or public transit directions from Transit and Trails:

GPS coordinates* for trailhead:
Latitude 3754'58.32"N
(* based on Google Earth data, shown as degrees, minutes, seconds)

Gas, food, and lodging:
Gas, pay phones, stores, and restaurants back around Camino Alto and Blithedale in Mill Valley. No camping in the immediate area.

Trailhead details:
Parking for about 4 vehicles in a narrow roadside pullout (parking is only available on the west side of the road, so it makes sense to approach the trailhead from Mill Valley rather than Corte Madera). This trailhead can be tricky to find. There are several likely-looking pullouts, but the one you're after is the first pullout past a wooden guardrail dotted with a multitude of reflectors, also on the right. If you miss the pullout (if you reach the crest of Camino Alto and the Mill Valley/Corte Madera border, you've gone too far), there is no parking available past the trailhead. You'll have to carefully turn around (I've done this at Chapman, which is the street just at the crest, and it's doable, but tricky), drive back downhill to Overhill, turn right, and then head back uphill on Camino Alto and try again. There are no parking or entrance fees. No drinking water, maps, or restrooms. No designated handicapped parking, and trails are not wheelchair accessible. There is no direct public transportation to this trailhead. You could pedal from bus stops on either Blithedale in Mill Valley or Tamalpais Drive in Corte Madera, but it's not a safe walk from either direction on Camino Alto to the trailhead.

Dogs are permitted on leash on trails; they are permitted off leash under voice command on fire roads, and dog owners must have a leash for each dog. Two Alto Bowl trails are multi-use, but no bikes are allowed on Bob Middagh and Horse Hill Trails.

The Official Story:
MCOSD's Alto Bowl page
MCOSD 415-499-6387

Map Choices/More Information:
• Use AAA's San Francisco Bay Region map to get there.
• Download preserve map pdf from MCOSD
• Open Spaces:  Lands of the Marin County Open Space District, by Barry Spitz (order this book from has a simple map and detailed trail descriptions.
• Hiking Marin by Don and Kay Martin (order this book from has a useful map and a suggested hike through Alto Bowl.
Friends of Horse Hill website.

Alto Bowl in a nutshell -- a printable, text-only guide to the featured hike.

View photos from this hike.

Go to Bay Area Hiker Home page

With US 101 just beyond its eastern border, TrailheadHorse Hill has a very public face. Many travelers lift their eyes from US 101 to the horse-dotted rolling hillside, and when in the early 1990's the property was threatened with a housing development, locals struck up a campaign to preserve the grassy knoll. Today, Horse Hill is part of the Alto Bowl Open Space Preserve, and the grazing horses are an historic link to a ranching legacy that's been mostly shrunk and pushed to the northwest corner of Marin County.
     While the hill itself is pretty, hiking so close to the highway never really appealed to me. Luckily the west side of Horse Hill is even prettier than the east, and much more peaceful. Although the entire preserve is squeezed between parcels of private property, Alto Bowl nicely illustrates the benefits of open space at the fringes of residential areas. Grass and oak woodland provide habitat for wildlife, and locals can take a daily stroll, run, or dogwalk on trails rather than sidewalks. Bob Middagh Trail
      Alto Bowl's trail network consists of two trails and two fire roads, strung together from Camino Alto to Lomita Drive. There's no parking on Lomita, so start a hike from Camino Alto and turn back when you've had enough. Most likely you'll want to walk all the way to Horse Hill, but if you happen to be stuck in traffic on US 101, a short stroll out-and-back on Bob Middagh Trail will probably perk your mood up considerably (and your dog's too). Evergreen trees along the trail don't provide much punch in autumn, and the trails get muddy in winter, but spring and summer are pleasant, particularly when there are wildflowers in bloom.
     Begin at the pullout on Camino Alto. Walk north on the side of the road about 120 feet, then turn right onto signed Bob Middagh Trail. View from Horse Hill Trail, back to Bob Middagh Trail and Mount TamA canopy of coast live oak, California bay, and buckeye shade the narrow trail, open to hikers and equestrians only. Beware of poison oak in the understory. Bob Middagh Trail heads north just downslope from Camino Alto, and as you walk you'll probably hear the "thump, thump, thump," of cars running over the Botts' dots on the center line. The trail steps out of the woods and curves right, while a shortcut path heads back uphill to Camino Alto on the left. Descending gently, Bob Middagh Trail passes through grassland, with coyote brush and broom dotting the hillside. On the left, groves of eucalyptus tower over a hilltop at the border between Corte Madera and Mill Valley. Look for California bays and oaks clustered around a rock outcrop on the right. The trail drops with a bit more conviction, and houses come into view straight ahead. Veering right, Bob Middagh Trail passes through a damp area lined with thickets of willow and blackberry.Horse Hill Trail Expect serious mud and standing water in winter. The trail rises a few feet to a clearing and unsigned junction at 0.46 mile. Turn right onto Alto Bowl Fire Road.
     The vegetation along the broad level, multi-use fire road is a mixture of natives and escaped ornamentals. There's plenty of red-berried cottoneaster, along with toyon, pine, oak, and broom. At 0.56 mile, the fire road ends at an open space gate. Just beyond, you'll reach a cul-de-sac and some houses. It feels like a dead-end, but look to the left for a diminutive wooden fence. One segment has a lowered board, and this "stepover" is the unsigned beginning of Horse Hill Trail. Turn left.
     The initial climb is quite steep on this eroded trail closed to bicycles. A few large houses sprawl to the right, but the sloping hillside on the left is still undeveloped. Some coast live oaks line the trail. At 0.72 mile, Horse Hill Trail crests and reaches an unsigned junction across from a power pole. Turn right to remain on Horse Hill Trail.
     The trail heads south through grassland, with oaks on the right and houses on the left.Take a look back to the north for impressive views of Mount Tam. You may be able to pick out Bob Middagh Trail as well.Looking west from Horse Hill There's a small pocket of coast live oaks where you might see hound's tongue in winter, and then Horse Hill Trail reemerges in grassland at a breathtaking viewspot. A fallen coast live oak, still majestic but near death, lies prostrate in the grass. The west flank of Horse Hill is visible. Although a likely-looking path heads straight along a plateau toward an oak, Horse Hill Trail bends left, skirting the fallen oak. The trail then angles across the hillside, squeezing through some broom so close to a few houses that I could smell laundry tumbling in someone's dryer. You'll reach a gate into the grazing section of Horse Hill at 1.00 mile. Watch your step, but it's nearly impossible to cleanly navigate the horse poop-lined path, which splits around a tree. Take either fork, and at 1.12 miles, you'll reach the crest of Horse Hill and the turn-around point for this hike. Bob Middagh Trail, on the return trip to the trailhead On a clear day the view extends to the San Francisco skyline. Traffic noise from US 101 is omnipresent. Horse Hill Trail ends at this hilltop, and Horse Hill Fire Road continues downhill to the west. (You can extend this hike downhill, but you'll have to climb back up when you reach the end of the fire road.) When I hiked here in January 2002, I was privileged to watch a pair of coyotes languishing in the grassland. The horses didn't seem to mind, although the neighborhood dogs were barking themselves into a frenzy. When you're ready, retrace your steps back to the trailhead.

Total distance: 2.24 miles
Last hiked: Thursday, January 24, 2002