Big Stone National Wildlife Refuge in west-central Minnesota protects a rare tallgrass prairie and wetland landscape at the headwaters of the Minnesota River. Shaped by glacial Lake Agassiz, River Warren, and ancient exposed granite bedrock, the area preserves prairie pothole wetlands formed as the Wisconsin glaciation ended. Modern refuge lands emerged after failed lake-control efforts on Big Stone Lake were reworked under the Flood Control Act of 1965 and transferred to the US Fish and Wildlife Service in 1975. Today its marshes, grasslands, and prairie remnants support more than 250 bird species, major waterfowl migrations, and several notable wildlife reintroductions.