From the back of the book:
Here's Mud In Yer Eye!
Actually, mud may be the least of your posse's problems when they're messing about on the mighty Mississippi River - especially near the mysterious mound city of Cahokia.
This strange collection of earthen mounds near St. Louis, Missouri, has baffled the best archaeologists from Back East, the identity of its builders lost to the mists of time. It's a deserted city shunned by people and animals alike.
Until now, that is. Something odd is going on in Cahokia - something sinister. The mound city's ancient builders have returned from a journey that's taken them outside the boundaries of time itself - and they're not the friendly folks they used to be!
This adventure for the Origins Award-winning Deadlands The Weird West roleplaying game pits your heroes against these ancient people and their mad plan to save the world from the horror of the Reckoning-by destroying it utterly!