The prairies can be very flat, to rolling hills, depending on where you are located at. Most of the soils, especially in North America, come from windblown silt called loess. In the north, the loess is on top of glacial sediments, and in the south, it is over river and old ocean sediments.no wrong , it got there by Glacier , scraped up from elsewhere and deposited.
if you genuinely want to learn about soil, start with learning about Geology first.