The OES visited the Seip Earthworks on July 10, 2006. Built by the Hopewell Culture sometime between 100 BC to 500 AD, the Seip Earthworks once enclosed about 121 acres, forming a small circle, an irregular circle and a square with 10,000 feet of embankment walls that were up to ten feet high. Inside this enclosure were several structures, a large mound at the center of the irregular circle, three smaller conjoined mounds, and some smaller mounds. Most of the earthworks were degraded or destroyed by agriculture and erosion, but several have been preserved and restored. In all, only ten percent of the earthworks are preserved in this roadside park. Seip Mound is the most recognizable feature of the earthworks today. At 240 feet long, 130 feet wide, and 30 feet high, Seip Mound is one of the largest burial mounds in the Middle Ohio River Valley. It contained over 100 burials and numerous artifacts, earning Seip Mound a place on the National Register of Historical Places.
Modern culture first published a survey and description of the Seip Earthworks in 1820. In 1846, the earthworks were again surveyed and published in the book Ancient Monuments of the Mississippi Valley. The Ohio Historical Society explored the three conjoined mounds from 1906 to 1909, and then excavated Seip Mound between 1925 and 1928. During Seip Mound's excavation, researchers discovered 122 burials and various artifacts, including thousands of freshwater pearls, Isle Royale copper, Carolina mica, and Tennessee River Valley effigy pipes. In 1971, archaeologists discovered impressions of the posts of a Hopewell house measuring 38½ feet long and 35 feet wide near Seip Mound. Further excavation revealed mica fragments, broken flint knives, pieces of pottery, and animal bones. It is believed that the house may have been occupied by the craftsman who made the artifacts found during the 1920s excavation.