PIERRE, SOUTH DAKOTA—Erosion of the banks of the Missouri River uncovers artifacts left behind by people ranging from prehistoric villagers through nineteenth-century fur traders who fueled the beaver hat craze. Evidence of prehistoric trade includes Knife River flint from North Dakota, obsidian from the Yellowstone area, and exotic materials quarried in other parts of South Dakota. Archaeologists also find fishhooks, squash knives, and hoes made from bison bones. “People now gravitate to the same areas for the same reasons that people for millennia have gravitated toward those areas—shade, shelter, resources. It provided a source of food and water,” said archaeologist Richard Harnois of the U.S. Army Corps of Engineers and the Omaha District’s Oahe Project Office.