Enjoy it while visiting Iowa City in Iowa
Devonian Fossil Gorge is a remarkable geological wonder located just north of Iowa City near Coralville Lake. This ancient ocean floor, dating back more than 375 million years, offers visitors a rare opportunity to walk through a prehistoric marine environment and observe well-preserved fossils embedded in limestone bedrock. The gorge was dramatically exposed in recent decades by floodwaters that stripped away layers of soil and vegetation, revealing one of the most significant fossil sites in the Midwest. What makes the Devonian Fossil Gorge particularly special is that the fossils here are not enclosed in a museum display but are fully exposed and accessible along a natural landscape that visitors can explore firsthand.
The story of the Devonian Fossil Gorge begins during the Devonian Period, when the region that is now Iowa City was covered by a shallow tropical sea. Over millions of years, the calcium carbonate remains of marine organisms accumulated on the seafloor, compacting into thick layers of limestone that would eventually form the bedrock underlying much of eastern Iowa. This ancient seabed remained buried beneath layers of sediment and soil for millennia, its fossil treasures hidden from view. That changed dramatically in 1993 when catastrophic flooding of the Coralville Lake reservoir stripped away the overlying soil and vegetation, exposing the underlying limestone bedrock with its extraordinary array of fossils for the very first time. A second major flood in 2008 revealed additional sections of the fossil-bearing rock, expanding the accessible exposure area.
Today, the Devonian Fossil Gorge stands as a living laboratory where amateur paleontologists, geology students, and curious visitors can observe ancient marine fossils in their natural setting. The University of Iowa maintains interpretive signage and self-guided tour information at the site, connecting modern visitors with the incredible biodiversity of Devonian seas. The most prominent fossils are the colonial corals that formed extensive reef structures, including species of Hexagonaria and Favosites. These corals built massive reef complexes across the shallow sea floor, similar in function to modern coral reefs but constructed by ancient marine organisms that have no direct living descendants.
Brachiopods dominate certain sections of the gorge. These dome-shaped, two-shelled marine animals attached themselves to the seafloor and filtered food from the water. Their fossils appear as distinctive symmetrical shapes pressed into the limestone, sometimes found in dense clusters that suggest thriving communities on the ancient seafloor. Crinoid fossils are among the most visually striking at the site. Often called sea lilies despite being animals, crinoids possessed long stalks anchored to the seafloor with feather-like arms that captured food particles. The gorge contains exceptional crinoid specimens, including rare articulated stems that can extend over a foot in length.
Exploring the Devonian Fossil Gorge combines nature walking with scientific discovery. The site features a 1,000-foot self-guided trail that winds through the exposed limestone bedrock, with marked focus areas highlighting significant fossil discoveries. The surrounding Coralville Lake area offers additional recreational opportunities including hiking trails, picnic areas, and scenic overlooks of the Iowa River valley. The trail through the gorge is relatively easy to navigate, with a firm limestone surface suitable for most visitors including families with children. Photography is a popular activity at the gorge, with visitors capturing images of the distinctive fossil specimens, the surrounding landscape, and the interpretative signage.
The Entry Plaza serves as the main gathering point for visitors, featuring hexagonal display plates made from Silurian dolomite that echo the structure of the fossil corals found throughout the gorge. Visitors can pick up self-guided tour leaflets here or obtain one from the Visitor Center at the dam. The address is 2850 Prairie Du Chien Rd NE, Iowa City, IA 52240, and the site is open year-round from 6am to 10pm daily. The best fossil viewing typically occurs in the morning or late afternoon when sunlight angles across the rock surfaces and highlights the three-dimensional detail of the fossils. Photography during these times produces the most striking images of the ancient marine specimens.
The most popular time to visit is during the spring and fall months when temperatures are moderate and the site is comfortable for extended exploration. Summer provides the longest days for exploration but the lack of shade at the gorge can make midday visits uncomfortable during heat waves, so early morning summer visits are recommended. Fall is arguably the finest season to visit, with cooler temperatures ideal for walking the trail and the surrounding deciduous forests displaying the rich colors of Iowa autumn. Winter visits are possible though challenging due to ice and snow on the rock surfaces, but the frozen landscape offers a dramatically different perspective on the ancient seafloor.