The Eminija Mounds are the largest and most numerous burial mound group in South Dakota, built by Native Americans of the Late Woodland Period and possibly dating from 500 to 1000 A.D. The original group had at least 38 dome-shaped burial mounds scattered irregularly for nearly a mile along the edge of the Big Sioux River flood plain northwest of this spot. It is supposed that the builders carried thousands of baskets of dirt to form each mound. Their original height is unknown, but they now stand three to four feet above ground level, and the largest range from 60 to 110 feet in diameter. Today only 15 remain substantially intact, while others have been destroyed by artifact hunters, agricultural cultivation, and natural erosion. Over the years, amateurs repeatedly dug into the mounds, sometimes using horse-drawn scrapers and dynamite in their searches for artifacts. In 1860, A.J. Hill, a St. Paul geographer, first visited, mapped, and named these sharply defined, highly visible mounds. Nine mounds have been excavated, beginning in 1869 by Dr. J.F. Boughter, a Fort Dakota surgeon. In 1883, A.H. Stites, later mayor of Sioux Falls, excavated the largest mound, then ten feet high, and reported boulder outlines of a turtle and two large fish on opposite sides, effigies that have since disappeared. Professional survey groups found skeletal remains of at least 78 humans. All original burials were below ground level, generally in the center of the mounds, with only a few associated artifacts, including objects of bone, red ochre, ornamental beads, disks made of local and marine shells, and a few ceramic pot shards in Woodland patterns. W.E. Myers of the Bureau of American Ethnology excavated several mounds in 1921 and believed there may also have been intrusive burials by both Ponca and Omaha Indians. All excavation studies have been partial and exploratory, and much remains to be learned about the people who built the mounds, their construction methods, burial practices, and accompanying artifacts. In 1986, through the vision and generosity of landowners Wendell and Eva Shafer, an easement for historic preservation in perpetuity was filed to protect the remaining 15 mounds, requiring that the surface area remain completely undisturbed as a cultural and historic resource for the people of this region.