Until the floods of 1993 at Coralville Lake, no one knew the gorge even existed. The floods of 1993 exposed some of the gorge, when flood waters rushed through the spillway of the Coralville Lake Dam, washing away the road, campground and huge amounts of river bottom silt and sand, exposing the Middle Devonian Cedar Valley Group limestones below.
While the flood waters in 2008 did some damage to the site, it was discovered that even more of the fossil bed had been exposed.
So, how did a hidden sea emerge in Iowa? Well, 375 million years ago, Iowa was actually located south of the equator. The area that is now the gorge was once a tropical sea, similar to the Caribbean. What remains in the gorge today are fossils of the plants and marine life that once lived and thrived in the sea’s waters.
When you arrive at the site, make sure to stop in at the Entry Plaza, where you’ll see displays that offer basic information about the site, including the dam, the floods that exposed the gorge, and the fossils that you’ll discover.
Once you’ve left the Entry Plaza, you’ll pass through a walkway lined with Devonian limestone boulders, each progressively older as you approach the gorge. The display highlights both the history of the limestone in the area, and its importance to Iowa’s economy.
Once you reach the gorge itself, you’ll find multiple discovery points where you can learn more about the fossils you’re seeing. When visiting the gorge, please keep in mind that damage or removal of fossils is strictly prohibited.
You’ll see diverse and well-preserved fossils in the gorge, including horn corals, brachiopods, crinoids (often called sea lilies) and more. You’ll also see old river sediments and imbricated slabs indicating the path and direction of the floodwaters.
If you want to learn more about Iowa’s geological history, you can make a stop at the Iowa Museum of Natural History, located at the University of Iowa in MacBride Hall, in downtown Iowa City. 17 N Clinton St., Iowa City, IA.
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