A devastating flood may have led to the demise of the thriving Native American city of Cahokia around 1200 A.D., according to research reported at the Geological Society of America conference. The community sprang up in an area near modern-day St. Louis and was just reaching the height of its population when the flood hit, after which Cahokia fell into decline and eventually became a ghost town. Researchers from the University of Wisconsin-Madison examined sediment cores from a lake near the Cahokia site, finding a layer of silty clay left behind by the floodwaters. "These floodplain lakes have been ignored for a long time as sources of these kinds of records, and they can be really valuable," said Samuel E. Munoz, a geographer who studies pollen records.
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