Marin County Parks and Open Space Department

This is a small preserve (37 acres), but it’s story is a perfect example of how many areas that are now open space were spared from development. As the town of Mill Valley grew in the late ‘60’s, the citizens realized that the surrounding ridges would soon be covered with buildings. Grassroots activism squelched the plans of several developers, and eventually the County was able to acquire the first 50 acres, which form the eastern half of the preserve.

Alto Bowl DetailThe southern half of the Alto Bowl Preserve is known as “Horse Hill” and is leased for horse pasturing by the Alto Bowl Horseowners Association. The sight of horses grazing peacefully on this grassy hillside has been a landmark for decades. Slated for development in the 1980s, the credit for its preservation goes to the horse owners, their supporters, the Marin County Open Space District, the Marin Community Foundation, and the City of Mill Valley who together raised 2.4 million dollars.

Dedicated volunteers have restored many acres of this preserve’s native habitats by waging an ongoing battle against French broom and other invasive, exotic plants. The Bob Middagh Trail connects the Alto Bowl Preserve with the Camino Alto Preserve to the west.


From Hwy 101 in Mill Valley, take the exit for E Blithedale Ave west for 1.4 miles. Turn right at Camino Alto, turn right at Azalea Dr, turn right at Vasco Dr (becomes Underhill Rd), and turn left at Coach Rd. MCOSD gate is at the end.

Visit,,, or dial 511 to find out about alternative transportation and public transit options from your location.

Open Space Field Guide

The open grasslands and forests of Alto Bowl are home to a thriving community of plants and animals. Coyotes and Bobcats are frequently sighted here. American Kestrels, Red-tailed Hawks and Northern Harriers are nearly always overhead, hunting for rodents and reptiles on the open hillsides.

eNature BirdsBirds
eNature ButterfliesButterflies
eNature ReptilesReptiles & Amphibians
eNature MammalsMammals
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Birds, Wildflowers


24 hours

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