To download soil information for your area, check out ESRI's SSURGO Downloader.
And why do we have such great topsoil here in Iowa? Partly because of the prairie environment that covered Iowa for thousands of years. For an easy view of what your county may have looked like, the Iowa Prairie Network publishes maps of the original landcover of each Iowa county. Or from the Department of Natural Resources GIS Data Library, you can download a shapefile version of the original Government Land Office survey from the mid 1800s.
Check it out and see if your home is on historical prairie, oak savanna, or something more surprising!