Devonian Fossil Gorge is the result of the prolonged overflow of the Coralville Reservoir Spillway between July 5 and August 2, 1993. This area is just south of the Coralville Dam (near Iowa City), managed by the Army Corps of Engineers.

From the Iowa Department of Natural Resources

The most abundant fossils in this area are crinoid stem fragments; these look like small washers such as you might find in a hardware store, and there are some layers exposed in the roadcut that are almost solidly made of these.