Some of the best collecting sites in Illinois are in the cliffs and bluffs along our major rivers, the Mississippi, Illinois, Ohio, Wabash, and their tributaries. At these places whole fossils are often weathered out and may be picked up easily. Well-known collecting sites for plant fossils are coal surface mines of Illinois. Perhaps the most famous is the Mazon Creek area near Braidwood in northeastern Illinois which has supplied beautifully preserved impressions of ferns, tree leaves, and a few insects to museums throughout the world. Many surface mines yield fine brachiopods , snails, clams and cephalopods .
Highway cuts through bedrock commonly expose beds containing fossils.
Be careful along road cuts, especially if there is heavy traffic. Stopping on Interstate highways is against the law. Extensive excavation of a road cut may be considered to be destruction of state property. Ice Age fossils, such as mammoth and mastodon teeth and tusks, have been found mostly in gravel pits but also in foundation excavations and ditches in all parts of the state. Most of Illinois' major rivers have bluffs covered by windblown glacial dust, called loess.