Anderson Marsh State Historic Park is a California State Historic Park and nature reserve preserving a tule marsh, archaeological sites of the Pomo people, and historic ranch structures. It is located in Lake County, California, USA. Anderson Marsh is located at the head of Cache Creek on the southeast corner of Clear Lake, the largest natural lake completely within the borders of California. The park is between the cities of Lower Lake and Clearlake on State Route 53, north of Calistoga in the wine country. The park is open year-round.