Pennsylvanian Period Fossils and Exhibits

During the early Pennsylvanian Period, northwestern Illinois was at the western edge of the Illinois Basin. The basin was a spoon-shaped depression that covered nearly all of Illinois, southwestern Indiana, and western Kentucky. It was a region of swamps and shallow seas, dotted by a few upland areas 15 to 30 meters (about 50–100 ft.) above sea level. This reconstruction is based on fossils and the preserved landforms from one of these uplands. They were uncovered in a quarry in Milan, Illinois.
Learn more about Mazon Creek and its fossils in our Mazon Creek Fossils online exhibit.