The Big Walnut Preserve, also called the Big Walnut Creek Preserve, is a 2,400-acre complex of largely forested lands located in Putnam County, Indiana, near Bainbridge. Identified as a beech–maple forest with a substantial admixture of tulip poplar, the wooded land parcel complex was designated as a National Natural Landmark in 1985. The complex is co-managed by the Nature Conservancy and by the Indiana Department of Natural Resources (IDNR).[1]