Pets are not permitted in Muir Woods. The park is very small and can get very crowded. To protect the wildlife, other visitors, and your pet, we suggest that you visit nearby areas such as the Coastal Trail at Muir Beach, and some trails in the Marin Headlands where they are permitted.
Service dogs, as recognized by the Americans with Disabilities Act, are allowed.
Marin County is a playground of trails for humans and their pets alike. The area is managed by several different agencies. Although Mount Tamalpais State Park does not allow pets on trails in general, dogs are permitted on leash on almost all trails of the Marin Municipal Water District and Marin County Open Space District.
Consider boarding your pet for a few hours at a nearby pet lodging facility. Please do not leave your pets in your vehicle. Your vehicle can quickly reach a temperature that puts your pet at risk of serious illness and even death, even on a day that doesn't seem hot to you. (Information from American Veterinary Medical Association.) Pets in vehicles left unattended in weather over 70 F can be removed and vehicles will be impounded at owner's expense.
Courtesy Jan Null, CCM; Department of Geosciences, San Francisco State University