Devonian Fossil Gorge Hike

Kids and adults can search for fossils at Devonian Fossil Gorge in the spillway at Coraville Lake north of Iowa City.

We walked a total of a mile finding fossils in the gorge and then walking along the road to where we parked.

The gorge is also scenic with its small pools with fish and other aquatic life along with going up short cliffs and around large rocks. (Main photo)

History of the Gorge

Created when water overflowed into the emergency spillway on July 5, 1993. This overflow continued for 28 days and reached 17,200 cubic feet per second, washing away a road, a campground, and removing up to 17 feet of soil and rock exposing the Devonian bedrock and forming this fossil gorge.

In 2008 floodwaters again swept through the gorge, with flow reaching 19,500 cubic feet per second widening the canyon significantly.

The water exposed a 375 million ocean floor with the gorge dating back to 200 million years before the dinosaurs.

*Learn about the geology of the area at the start of the hike.*

Beginning the Hike

Paved at the start and leads to a plaza. Blue hexagon markers lead you to information about the gorge and fossils. The sidewalk leads down to the gorge and then the trail is on the natural surface of the gorge. Careful walking around here since it is a rocky surface and is not level.

Hexagon one found in the plaza. — *Hexagon one found in the plaza*.

Hexagon 1

The monoliths in the plaza are made from a sedimentary rock called limestone. Hexagons on the monoliths in the plaza have information about the fossils and geology of the area.

Hexagon 2

Along the sidewalk, you will find five boulders going from the youngest to the oldest formation. The first boulder has scratches, called glacial striations, from the most recent glacial episode one million years ago. Observe how the boulders change in color and fossils increase with depth.

Hexagon 3

Now we headed into the gorge. Above hexagon three in the rock you will see colonial coral called Hexagonaria (named for its six-sided shape) and the honeycomb-like Favosites.

These colonial corals created reef-like structures similar to what we find in tropical seas today along with a habitat for many Devonian creatures.

Hexagon 4

Found in these rocks are Crinoids. They are also called “sea lilies” due to their flower-like resemblance. Related to modern-day anemones and starfish.

The crinoid lived anchored to the sea floor by flexible, segmented stems, and used their tentacle-like arms to capture and filter food from the ocean current.

Hexagon 5

The solitary horn corals resemble bugle chips. Horn corals can range in size from less than an inch to many inches in length. These corals live alone and unattached, unlike colonial corals. Also, the rust color in the limestone is a chemical reaction called iron oxidation. This reaction is the same that causes rust on your car or old nails.

Hexagon 6

A white crack here is calcite. Many sea organisms make their shells out of calcite by pulling carbon dioxide from the seawater. As these organisms die, their shells, coral, or other debris accumulate on the sea floor, forming limestone. An interesting chemical property of calcite is its ability to effervesce, or fizz, with hydrochloric acid.

Hexagon 7

You are now standing on the roof of a collapsed cave, formed by groundwater eroding the limestone over a long period of time. Over time, erosion exposed the colonial coral that you can see here today.

Hexagon 8

Looking north toward the overflow spillway, you will see examples of karstification. Groundwater dissolved parts of the bedrock and is responsible for the irregularly shaped limestone.

Hexagon 9

At this point, you will notice slabs of limestone that dip down toward the direction of the floodwater. The 2008 flood created this boulder-thrown landscape.

Hexagon 10

Deposited by an ancient river was this mysterious mound. It contains poorly sorted sand and gravel including small igneous pebbles, which is a clue that it was brought down by glaciers.

Hexagon 11

This is the largest fault zone of the gorge. A fault is a break in the earth’s crust along which movement occurs. The pattern of down-drop limestone blocks is caused by faults and folds. All faults in the gorge have been inactive for millions of years.

Hexagon 12

Couldn’t find the hexagon, but it marks the asphalt trail that we used to go back to the parking area.

Final Thoughts

My son enjoyed finding the hexagons along the trail. I read him the descriptions so we could figure out what we were seeing along the way.

More information online at: https://www.mvr.usace.army.mil/Missions/Recreation/Coralville-Lake/Recreation/Devonian-Fossil-Gorge/

*Note: A lake is located towards the end of the walk.*

DETAILS

NOTE: The nearest restrooms are located at Tailwater West Campground.

Drive: From St. Louis take U.S. 61 north. In Wayland keep going straight ahead onto Highway 27 which becomes U.S. 218. In Iowa City take exit 89 toward Riverside Drive and continue on Old Highway 218 going north which becomes Riverside Drive. Make a right on Park Road then a left on Dubuque Street and then a right onto Overlook Road NE. Next a right onto Prairie Du Chien Road and then another right and look for parking for the fossil gorge on the right.

Hours: 6 a.m. – 10 p.m. daily

Address: 2850 Prairie Du Chien Rd NE, Iowa City, IA 52240

MORE TOURIST STOPS ON THE WAY TO IOWA CITY

We drove to Iowa City from the St. Louis area. Along the way, we stopped at the Columbus Junction, Iowa Swinging Bridge and, the Battle of Athens near the Iowa and Missouri border.

Touring the Battle of Athens State Historic Site

A walk through history as you tour mill ruins, historic homes, and a battleground at the Battle of Athens State Historic Site. The site is located about three hours north of St. Louis near the Iowa border. General Store We first stopped at the former Athens, Mo., General Store.