From 290 million to 1.8 million years ago, Illinois must have been a hotbed of geological, biological, and climate change, but clues about what happened here during this long interval are mostly missing.
The Age of Dinosaurs and most of the Age of Mammals came and went without leaving much trace in Illinois. Rocks were either not deposited, or they were eroded away.
During this time Illinois moved from its position just south of the equator to a position about 4,500 kilometers (2,800 miles) north of the equator. The environment varied widely throughout this time interval—from tropical rain forests to dry deserts.