Well, I'm from Illinois, and though I don't live near Cahokia, I've been there. Cahokia is the center of the Mound Builders culture. Although many tribes buried their dead in mounds, most such mounds are rather small. From around 600 AD - 1400 AD, the Cahokia mound builder culture existed. It is believed that the extremely fertile soil along the banks of the Illinois and Mississippi rivers allowed these people to grow an excessive amount of corn (more than they could possibly eat themselves) and began to export the corn for trade among other lesser successful tribes across North America. Most native tribes live as hunter/gatherers or the most primitive neolithic agriculture techniques - most tribes spent the majority of their time finding enough food to survive. Because the Cahokia people had more food than they could eat, their culture advanced. Most tribal warriors spend a part of their time defending their people, and most of their time hunting and doing other chores in order to survive. Cahokia warriors were full-time soldiers, and the rest of Cahokia society was an early form of a caste system. Cahokia had full time religious practitioners and other full time workers in their specific niche. The Cahokia mound pyramids are the largest in the world, larger even than the Egyptian pyramids, though the Cahokia didn't use brick, rather rammed earth as their building medium, but they built literal mountains of dirt, capped by temples.

Although restored without full assurance of accurately depicting the original art, but the surface side of one of the earthen mounds had art of a giant thunderbird - believed by native Americans to ride the stormfronts from the south to periodically visit their region. Cryptozoology suggests these birds were/are real (I've known people who claim to have witnessed them in this area). I am sure their are other examples of Cahokia art, but the giant thunderbird on the mound has been reported since the French arrived here in the late 1600's, and was seen as late as the early 20th century. In the 1970's a native artist recreated the thunderbird, as by current times all traces of that art were gone.

It is believed climate change ended Cahokia society.