Topsoil in the plains was many feet prior to the dustbowl. Probably not everywhere but many prairie plants have roots down to 15-20 feet. Topsoil is what we c

Topsoil in the plains was many feet prior to the dustbowl. Probably not everywhere but many prairie plants have roots down to 15-20 feet. Topsoil is what we call the upper "living" aerobic portion of soil. It is the portion of soil that participates in nutrient cycling. Roots into subsoil turn it into top soil over time. Tilling kills topsoil. So, its not that all the dirt flew away. Some did, but mostly it just died and turned back into subsoil.