Bale Grist Mill State Historic Park 3369 Saint Helena Hwy N, Saint Helena, CA94574-9660 Bale Grist Mill State Historic Park is a public park operated by the state's parks and recreation department. It…More features a wind-powered mill originally constructed in 1846, for use by Napa Valley settlers to grind corn and wheat and serve as a prominent social center. The parks amenities include hiking trails, picnic areas and more. Tours and milling demonstrations are available on weekends. The park is also open to school groups on Tuesdays by appointment.