Here are some pictures I took at the Devonian Fossil Gorge, near Iowa City. The Gorge is the result of the overflow of Coralville Reservoir Spillway between July 5 and and August 2, 1993. 
This area is just south of the Coralville Dam, managed by the Army Corps of Engineers. It is the product of the '93 flood, during which the water level behind the dam rose to over 4.5 feet above the crest of the spillway and poured over in a torrent, tearing away vegetation, pavement, topsoil, sediment, and loosely cemented bedrock from the area downhill from the paved spillway apron and even tearing into the solid limestone bedrock in some places. For 28 days as much as 17,000 cubic feet of water per second flowed down the Spillway. Fifteen feet of unconsolidated river-bottom silt and sand were rapidly eroded, exposing the Middle Devonian Cedar Valley Group limestones below. Up to 5 feet of limestone was then eroded near the end of the Spillway, and blocks weighing as much as two or three tons where carried hundreds of feet downstream. When the flood abated, the eroded Gorge surface revealed a succession of 375 million year old bedding planes with diverse and abundant fossils commonly standing out in relief. 
The fossils are amazing...
If you click on these pictures you can explore by zooming-in and seeing even more Devonian fossils! Make sure you zoom-in on the one at the very top of this post, also! The area really is a window into Iowa's geologic past. (Hard to believe that Iowa once was covered by warm, shallow seas similar to the Caribbean Sea today.) I really enjoyed walking around the area, taking it all in, and thinking about what has past here before...
