Effigy Mounds National Monument at English => English (The Britannica Concise) Of Explained:
National preserve, NE Iowa. Located on the Mississippi River, it covers 1,475 acres (597 hectares). Established in 1949, the monument has 183 known mounds, some of which are in the shape of birds and bears. The mounds were built over the course of the Woodland period (1000 BC-1200 AD), with the effigy mounds probably constructed between AD 400 and 1200. Some of the mounds have yielded copper, bone, and stone tools of Indian origin. One of the bear mounds is 137 ft (42 m) long and 3.5 ft high.