I've seen parts of southern Iowa where there is zero top soil left. There are many hilly areas around there and resulted in the exposed top soil from "traditional" row crop farming easily washing away in heavy rains. It should never have been farmed to begin with. Once it became unusable for row crop farming they just put cattle on it which causes even more erosion. Because the ground is mostly only clay now any rain easily causes flooding. The best part is where a lot of the farmers there dump all their trash in the ravines (tires, appliances, household garbage, etc) that are formed from all the erosion to create some form of "erosion control".
