My family farm is in NW Iowa -- O'Brien county. For the past 3 years, this county has the highest land value of any Iowa county. When I was a kid digging holes for corner fence posts, we could dig down as deep as 5 feet before running into blue clay. Glacier-formed lakes were just a few miles away.
Northern Iowa has great soil. Southern Iowa soil is mostly crap, so much of it is grassland & woodland.
The upper Midwest has the best soils. I'm talkin' the Cornbelt for sure.
Proud subscriber of TURF Magazine. (thanks Ron)