Searching the banks of the Mazon River for fossils. Photo courtesy of http://www.flickr.com/photos/lapstrake/2391568434.

Ever since I was old enough to pick up a pebble, I’ve been fascinated by rocks. By the time I was a teenager, I had become a passionate rockhound, hauling boxes of specimens back from every family vacation. Over the years, my collection grew to include some fine specimens. I specialized in minerals that had been buried in the earth for eons, gradually forming sparkling, multi-colored crystals. Some, I bought. Some I dug from the ground. Others came my way when I traded with other rockhounds.

I added to my collection whenever I traveled, since the Chicagoland area offered little in the way of mineral collecting. But that all changed when I moved 60 miles southwest of Chicago to the town of Morris, Illinois and rented an apartment on the shores of the Mazon Creek. Here, in the midst of endless flat plains, I discovered one of the word’s greatest fossil collecting sites.

Three hundred million years ago, this area of Illinois was dominated by shallow seas and swamps. As plants and animals died, they fell into the water and were covered with successive layers of mud. Bacteria caused the organic matter to decompose inside the mud, producing a carbon dioxide “bubble” in the sediments around the remains. The carbon dioxide combined with iron from the groundwater to form an ironstone nodule. Gradually, the layers of mud in which the nodule was embedded hardened into shale.

Oval nodule embedded in layer of shale is certain to contain a fossil

Semi-rare Annularia specimen

Since these oval-shaped nodules are some of the finest fossil specimens in the world, they are highly sought by collectors. Following every rain, rockhounds descend on the Mazon Creek to search the shallows of the river and its exposed banks. While much of the river runs through private property, there are many access points on public lands, and even a site that is devoted to fossil hunting at the Mazonia Braidwood State Fish and Wildlife Area.

Neuropteris specimen

Kids are absolutely astounded when the nodules are struck with a hammer and split into two halves, revealing a perfectly preserved leaf or animal. For a more perfectly preserved fossil, place the rocks in a freezer overnight and then drop them into boiling water. Not only is fossil hunting fun for the whole family, it is an excellent educational activity. And if you’re really lucky, you may find a specimen of the elusive Tully Monster, which was was designated the Illinois State Fossil in 1989 and is only found in and around the Mazon Creek.

Fossilized remains of the unique Tully Monster are found only around the Mazon Creek

In addition to rockhounding, north central Illinois offers abundant fishing, hunting, boating, birding, and hiking opportunities, as well as numerous local attractions and festivals throughout the year, and a wide range of accommodations are readily available.

Article by Barbara Weibel of Hole In The Donut Travels