Much of that topsoil is now located as silt in the river deltas along the coastlines.

@OldGoat43 Not? or Now?

@Robecology. Sorry. Badfinger.

@OldGoat43 I did more research...and you have a point...some of that was natural erosion...

But I found this, when I googled "loss of Topsoil in America"

On average, farmed fields were 1.2 feet below the prairie, per Science News. After measuring soil height in each area, the team found that, on average, topsoil is eroding at a rate of 1.9 millimeters per year, Harvest Public Media reports.Apr 19, 2022.

So my estimates were modest/low.

[smithsonianmag.com]

Most farmland in our country was grassland which only had a few inches of topsoil. Modern farming relies mostly on chemical fertilizers, herbicides and pesticides.

@OldGoat43 The prairie was centuries in the making of fertile soil thru fire & renewal. The 1st Euros thought it was unfertile as there were few trees. Discovering just how deep the earth was resulted in the destruction of our prairie & the Dust Bowl. Modern farming is depleting & toxic. Few minerals remain. My virgin soil on 4 acres is 10 inches deep with black rich soil on a layer of clay. I have a mix of prairie & oak savannah never plowed & full of native plants.

@Mooolah . Bison droppings on the plains and leaves from the forests made many areas fertile but not all of it was gifted the nutrients. It took me ten years to enrich the rocky clay on my farm in upstate New York with my composting work. Here's a photo of one of my crops with my girlfriend.
Where are you living now?

@OldGoat43 I am in southern Wisconsin which used to be more progressive than Illinois. I may move back as cannabis is legal there & Wisconsin ain't what it used to be. That photo made me salivate. Gorgeous.

@Mooolah . I've lost the farm due to over taxation from NY State. They wanted more taxes from residential land rather than farm land. I've moved to central Pennsylvania and now grow cannabis in my basement with lots of grow lights.

@OldGoat43 Indica or Sativa?

@Mooolah. Mostly indica, White Widow strain. Grown in 50-gallon pots of my mix of soil and earthworm castings, under six banks of 1000 watt LED fullspectrum lights hung from the basement ceiling. The whole setup only draws about 600-700 watts of power. All on one timer set at 16 hours of light & 8 hours of darkness.