At 62ft high and 240ft in diameter, the Grave Creek Mound in the Ohio River Valley in West Virginia is one of the largest conical-type burial mounds in the United States. The builders of the site, members of the Adena culture, moved more than 60,000 tons of dirt to create it about 250–150 BC. The earthwork mound is located in present-day Moundsville near the banks of the Ohio River.The first recorded excavation of the mound took place in 1838, and was conducted by local amateurs. The largest surviving mound among those built by the Adena, it has been designated a National Historic Landmark.In 1978 the state opened the Delf Norona Museum at the site. It displays numerous artifacts and interprets the ancient Adena Culture. In 2010, under an agreement with the state, the US Army Corps of Engineers gave nearly 450,000 artifacts to the museum for archival. These were recovered in archeological excavations at the site of the Marmet Lock, and represent 10,000 years of indigenous habitation.DescriptionGrave Creek Mound is the largest conical type of any of the mound builder structures. Construction of the mound took place in successive stages from about 250–150 B.C., as indicated by the multiple burials at different levels within the structures. In 1838, road engineers measured its height at 69ft and its base as 295ft. Originally a moat of about 40ft in width and 5ft in depth, with one causeway across it, encircled the mound. Inside the mound, archaeological researchers have discovered Adena Hopewell remains and ornaments, along with a small sandstone tablet, the Grave Creek Stone, believed by modern scholars to be a hoax.