Most fossil plants and animals from hundreds of millions of years ago were preserved in swampy lowland areas where they had the good fortune to die and be buried quickly by sediments in water. The water preserved the specimens long enough for the living tissues to be replaced by minerals or for the specimen to create an impression in the soft mud that hardened into shale or sandstone under heat and pressure. The fossils collected at the Allied Stone Company, located between Rock Island and Milan, Illinois, represent a different habitat, one that was higher in elevation and well drained, and less favorable for preserving fossils. These less common fossils help scientists broaden their understanding of plants, and sometimes animals, that lived in uplands. Scientists also gain more insight into diversity of species and the evolutionary progress that was underway 300-350 million years ago.

Fossils collected at this site represent plant species from the late Mississippian and early Pennsylvanian periods (known together as the Carboniferous period where carbon stored in plants is preserved today as coal). Dr. Richard Leary, Geology Curator Emeritus of the Illinois State Museum, collected fossils at the site for several years beginning in 1970. While the site yielded mostly plants, a few animals also have been found, including a fossil scorpion that was used to describe a new species (Labriscorpio alliedensis). The specimen used as the standard for the new species is known as the holotype. The collection from Allied Quarry is impressive, taking up two aisles of cabinetry in the Research and Collections Center.