During the middle of this period the temperature became warmer and dryer than today. Prairies expanded into areas that are now covered with forests. Some areas had active sand dunes that were shifting across the land, just like those that are found in the deserts of the southwest today.
At the end of the period the temperature became similar to what we are familiar with today. Water levels on Lake Michigan also fluctuated greatly during this time. Sometimes the lake levels were higher than today, and at other times they were lower. Rising lake levels have left some Archaic sites under water.