Marin County Parks Open Space Leash Policy: Dogs on leash are welcome to enjoy trails. Dogs are allowed off-leash under strict voice control on fire protection roads. Please follow posted rules.

The 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.

When you drive up Coach Road toward the preserve’s gate, you’re entering land that locals fought hard to keep open. The rolling meadows here feel worlds away from the highway below, even though you’re just minutes from Mill Valley’s main drag. In spring, wildflowers dot the grassy slopes, and year-round you’ll see those characteristic horses moving across the hillside—which is why keeping your dog leashed on the main trails matters. If your dog hasn’t spent much time around horses, a startled reaction could spook them or create a dangerous situation for everyone.

Dedicated volunteers have restored many acres of this preserve’s native habitats by waging an ongoing battle against French broom and other invasive plants. The restoration work is visible as you walk—native oak woodlands and grasslands are slowly reclaiming space from the exotic species that had taken over.

The Bob Middagh Trail connects Horse Hill with the Camino Alto Preserve to the west, giving you options to extend your walk. The network of trails here ranges from gentle slopes to steeper climbs, and the elevation gain offers views back toward the bay. The fire protection roads allow off-leash walking if your dog has reliable voice control, giving you more flexibility once you’re away from the horse pasturing areas.