The gallery below will contain a mere sampling of more than 400 flora and 300 fauna that have been identified in the Mazon Creek assemblage. The astonishing diversity includes cnidarians, echinoderms, worms, snails, clams, shrimps, eurypterids, fish, hexapoda (including insects, millipedes, centipedes), arachnids (scorpions and spiders) amphibians, and horseshoe.

The Mazon Creek fossils are conservation lagerstätten found near Morris, in Grundy County, Illinois. The fossils are found in ironstone concretions, formed approximately 300 mya in the mid-Pennsylvanian Epoch of the Carboniferous Period of the Paleozoic. These concretions frequently preserve both hard and soft tissues of faunal and floral life, including many soft-bodied organisms that rarely fossilize.

The majority of the Mazon Creek collecting areas are the spoil heaps of abandoned coal mines, and the most famous of these is Peabody Coal Pit 11. Pit 11 now serves as a cooling pond for the Braidwood nuclear power plant, but with over 100 other localities, specimens still are found.