Fort Thompson Mounds is a major archaeological complex along the Missouri River in central South Dakota, where a chain of low earthen burial mounds extends for about 6 miles above the bottomlands. Generally linked to the Plains-Woodland period beginning around 800 CE, the site has produced evidence of some of the area’s earliest pottery-making peoples. Excavations also revealed far older cultural deposits, including a radiocarbon date of about 2450 BCE, showing nearly 5,000 years of Indigenous occupation. Salvage archaeology beginning in 1957 documented burials, hearths, pottery, and stone tools before dam construction and inundation. The complex became a National Historic Landmark in 1964.