That “pyramids and plaza” look to the artist’s conception drawing is evocative of PreColumbian Mexico and Central America, and the culture appears to have spread up the Mississippi; furthermore, two-way trade of goods over thousands of miles has been documented in recent decades. However, piling up dirt results in a pyramid-like pile of dirt, so...
See #7. Some archeologist argue that the migration went the opposite direction — from WI to Mississipi to Mexico City.
It's frustrating and tantalizing to realize there was a flourishing and sophisticated culture in that region but without a written language or permanent structures we know so little about it.