Mazon Creek, Paleontological site in Grundy County, Illinois, United States.
Mazon Creek is a paleontological site in Grundy County, Illinois, known for its remarkable fossils from the Carboniferous period. The remains lie within rounded ironstone concretions often found along creek beds and in old mining spoil heaps.
The fossils date from the Pennsylvanian epoch around 309 million years ago, when the region was covered by shallow seas and coastal swamps. Official recognition as a National Historic Landmark came in 1997, honoring the scientific importance of the deposits.
School groups and collectors often visit the area on weekends to search for fossils and learn how to extract them from the concretions. Local communities see the area as a window into a time when swamps and tropical forests shaped the landscape.
Collecting specimens requires a permit and should only happen in designated areas to avoid disturbing the deposits. It helps to go during dry weather, when concretions are easier to spot along exposed surfaces.
Many specimens show soft tissues and details like wing patterns or skin texture that usually disappear in the geological record. The mineral process acted like natural preservation, protecting even delicate body parts from decay.
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