Effigy Mounds National Monument preserves more than 200 prehistoric mounds built by pre-Columbian Mound Builder cultures, mostly in the first millennium AD, during the later part of the Woodland period of pre-Columbian North America. Numerous effigy mounds are shaped like animals, including bears and birds. The monument is located primarily in Allamakee County, Iowa, with a small part in Clayton County, Iowa, in the midwestern United States.