Mazon Creek Locality

Map showing location of Mazon Creek fossils

Ironstone concretions containing Mazon Creek fossils are found in various types of natural and man-made outcrops of a rock called the Francis Creek Shale.

Most of the fossils come from the Mazon Creek area of Grundy, Will, Kankakee, and Livingston counties. In this area fossils are recovered from natural exposures on Mazon Creek, from active and abandoned strip mines, from shaft mines, and from mine spoil piles.

Fossils like those from Mazon Creek are recovered from a few other areas in Illinois. The Francis Creek Shale is exposed along streams and in strip mines in LaSalle county between the Vermillion River and Marseilles.

Mazon Creek nodules and fossils are also found in museums worldwide. This is because the fossils from the area are abundant and exceptionally well-preserved. Most major natural history museums in the world probably have at least a few nodules.

The most important collection of Mazon Creek nodules is probably at the Field Museum of Natural History.

The Illinois State Museum also has an important collection of Mazon Creek fossils, including numerous type and figured specimens. Some of these fossils are shown in this exhibit.