It came back as St. Louis. :^)
I live in this latitude of Illinois, there is a huge hill within about 15 miles of me that is said to be of the Indians. Plus Burrows Cave is within about 20 miles in the other direction, although the artifacts from that cave seem to be from thousands of years ago instead of from Cahokia's accepted era. Maybe there was a major Indian thouroughfare along the approximate route of Route 40 and Interstate 70. I'll have to keep my eyes open for anomalies when I'm out mushroom hunting. :^)