Sugarloaf Ridge State Park is a state park in Northern California, United States. Located in the Mayacamas Mountains north of Kenwood, the park straddles the boundary between Sonoma and Napa counties. The park contains the 2,729-foot Bald Mountain and the headwaters of Sonoma Creek including a 25-foot tall seasonal waterfall. The park is also home to the volunteer-run Robert Ferguson Observatory.