(Radio Iowa) –  Repeated Mississippi River flooding is threatening prehistoric burial mounds that comprise Iowa’s only national monument, and the U-S Army Corps of Engineers is looking for public input on plans to protect the area. Kim Warshaw, the Corps’ project manager, says the Effigy Mounds National Monument in Harpers Ferry is being placed at risk by the lock-and-dam system, climate change, land use changes and altered hydrology.

Warshaw says shoreline erosion is causing “irreparable and unacceptable damage” to the ancient mounds, believed to have been built during the first millennium. The Corps is looking to use river sand and rock to stabilize the shoreline to ensure the rare mounds aren’t lost forever.

Marching Bear mounds at Effigy Mounds. (National Park Service photo)