Burial sites presumably lost to history in southeast Iowa may be rediscovered after all.

Researchers at the University of Iowa report using magnetic imaging to locate ancient indigenous burial mounds on land that had been plowed and leveled. In the study, the researchers identified at least six flattened mounds at a farm in southeast Iowa that are associated with the Havana Hopewell culture. This indigenous group lived in Iowa and other parts of the Midwest from about 100 BC to about 300 AD.

“Mounds and earthworks are highly susceptible to damage by agricultural practices,” the researchers write, but careful measurement of soil magnetism shows that “leveled mounds are detectable and may retain subsurface integrity even when above-ground evidence has disappeared."

While magnetometry has been shown to be useful to identify signs of ancient communities, “we showed that we can also locate mounds by measuring soil magnetism,” says John Doershuk, head of the Office of the State Archaeologist at Iowa. “These mounds may have features such as burial pits that are still partly intact below the depth of plow disturbance. Earlier magnetic studies in Ohio had identified flattened earthworks—geometric enclosures with infilled ditches—but not burial mounds."

The study is titled, “Geophysical Detection and Assessment of Leveled Mounds: An Example from the Upper Mississippi Valley.” It was published online in early January in the journal American Antiquity. The study’s corresponding author is William Green, former head of Iowa’s Office of the State Archaeologist, with co-authors from the Midwest Archeological Center, National Park Service.