The term “gumbo” is quite generally understood by the farmers of this state to refer to a very dark colored, heavy type of soil, occurring on certain flat areas, either river bottoms or the very level uplands. Usually it is inky black. It is more adhesive and bakes more easily than any other type of soil in this state. Yet any one who has had experience with gumbo will testify that it can at times be put into excellent tilth, having a fine mealy appearance, which is quite deceptive of its real nature. A seed bed will sometimes work up as mellow as an ash heap and remain so all summer if it is not puddled by being stirred while too wet.
Stevenson, W. H. and Barker, J. F.
"The Gumbo soils of Iowa,"
Bulletin: Vol. 10
, Article 1.
Available at: https://lib.dr.iastate.edu/bulletin/vol10/iss119/1