Hartley Fort State Preserve features the remains of a prehistoric fortified village. This 2-acre, privately owned preserve is located along the Upper Iowa River in Allamakee County. Early archaeological investigations of this area date back to the late nineteenth century. The site was studied by the Office of the State Archaeologist in 1964 and was dedicated as an archaeological state preserve in 1970. Additional studies were carried out by the Office of the State Archaeologist in 1993. The preserve sits on a terrace marking the position of an ancient floodplain. As the river meandered across the valley between 14,000 to 17,000 years ago, it deposited alluvium whose surface is now about eighty feet higher than the present valley floor. The first known human occupants of this site, about a.d. 1000, were Woodland Indians. They constructed a large, square palisade or stockade reinforced by a ditch and earthen embankment to enclose the main village area. They also constructed nine conical mounds near the village. Later, Oneota people also occupied the site. Ceramics collected from the preserve have shown influence from the Mill Creek culture of northwest Iowa and the Late Woodland culture in southern Wisconsin. The site is significant for understanding the interaction of late prehistoric groups in the Quad-State Region of the Upper Mississippi River valley. The human remains recovered from the site have been repatriated to the Iowa and Otoe-Missourian tribes and reburied.