The mounds were built by an Effigy Mound tribe, ancestors of the Oneota, between 500 and 1050 CE. About 950 years ago mound construction stopped, and Effigy Mound people seem to have abandoned most if not all of the interior hill country of western Wisconsin. Archaeologists have suggested that human populations in the region became too large to be supported by wild resources.
White-tailed deer may have become scarce in the open oak savannas and prairies of western Wisconsin, and the Effigy Mound people might have had too few deer to survive the winters. It is at the end of Effigy Mound time that these people begin to grow corn, suggesting that their needs were no longer met by wild resources.
