The following reply to the comments by Nolan and Cook makes the following points. The Palmer Drought Severity Index (PDSl) is not a measure of summer rainfall. Cahokia's "Big Bang " dates to the end of the Edelhardt phase and continued through the Lohmann phase. The "American Bottom " refers only to the Mississippi River floodplain in the vicinity of East St. Louis, and the exact nature of human response to climate change cannot be predicted from PDSI data alone.
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