E-Mail IMAGE: Archaeologists at Washington University in St. Louis found scant evidence that 'wood overuse' at Cahokia caused local flooding and subsequent collapse. view more Credit: Joe Angeles / Washington University Whatever ultimately caused inhabitants to abandon Cahokia, it was not because they cut down too many trees, according to new research from Washington University in St. Louis. Archaeologists from Arts & Sciences excavated around earthen mounds and analyzed sediment cores to test a persistent theory about the collapse of Cahokia, the pre-Columbian Native American city in southwestern Illinois that was once home to more than 15,000 people. No one knows for sure why people left Cahokia, though many environmental and social explanations have been proposed. One oft-repeated theory is tied to resource exploitation: specifically, that Native Americans from densely populated Cahokia deforested the area, an environmental misstep that could have resulted in erosion and localized flooding.