 | This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. (August 2018) |
| Nachusa Formation | |
|---|---|
| Stratigraphic range: Ordovician | |
| Type | Formation |
| Location | |
| Region |  Illinois |
| Country |  United States |
The Nachusa Formation is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.