In the Summer of 1993, a torrential flood overcame this area of the midwest. Finally the spillway at the Coralville Dam (which had never been utilized up until this point), overflowed exposing fossils over 300 millions years old.
It is an interesting place to visit and one full of history, check out the following links if you would like further information on the gorge.
http://www.mvr.usace.army.mil/coralville/devonian_fossil_gorge.htm
http://www.icccvb.org/members_details.asp?I=51
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