Ten burial mounds at Oakwood Lakes, typical of numerous mounds in eastern South Dakota, date from about A.D. 300 to A.D. 1400 and were probably left by late Woodland or Middle Missouri cultures. All are strikingly similar, about 3 to 6 feet high and about 100 to 150 feet in diameter. The people who built them made pottery, stone hammers, and projectile points that may still be found in the area. Whatever purposes the mounds may have served, whether fortification, shelter, or religious use, nearly all that have been excavated have contained human remains. These remains show both primary burials, with skeletal remains in natural arrangement, and secondary burials, in which bones were gathered from an initial burial, possibly a scaffold-type burial, then wrapped in skin or bark and reinterred, often scattered randomly in the pit. One or several individuals may be buried in each mound, which were likely built by people carrying baskets of earth on their heads and dumping the dirt to form the mounds.