JW, the whelk shells went all over the Deep South, Midwest, and southern Great Plains. Those mound builders were able to obtain materials from all over the continent. Just as a sampler, they obtained canel coal from the Dakotas, copper from the Great Lakes, white shark teeth from the Atlantic, Mica from the Appalachians, igneous rock form the Ozarks, and . . . well you get the idea. They had a trade network, and perhaps sent people on long trips to get what they wanted.
Amazing folks. Too bad we know so little about em.