Morrison Formation

Composition and depositional environments

The lithology of the Morrison includes mudstone, sandstone, siltstone and occasional limestone. Colors range from light gray and greenish-gray to reddish tones. These rock types record sediments laid down in rivers, floodplains, lakes and shallow ponds. Most vertebrate fossils are recovered from greenish siltstones and lower sandstone beds that represent former channels and overbank deposits of ancient rivers and floodplains active during the Jurassic period.

Fossils and scientific importance

The Morrison is celebrated for a diverse vertebrate fauna that includes large sauropod and theropod dinosaurs, stegosaurs, and many smaller animals, plus fish, turtles, crocodile-like reptiles and plant remains. Classic genera recovered from Morrison rocks include some of the most familiar names in paleontology. These fossils have been central to research on dinosaur anatomy, ecology and behavior, and they continue to inform studies of Late Jurassic terrestrial ecosystems.

History of study and geographic extent

First recognized in the late 19th century during geological surveys, the Morrison Formation became a focus for paleontologists during the bone wars and later systematic fieldwork. It extends through several states, appearing in badlands, cliffs and quarries where erosion has exposed the layers. Because the formation varies in thickness and local appearance, regional studies correlate its members across basins to understand ancient environments and sediment sources.

Uses, distinctions and notable facts

• Scientific value: a primary source for Late Jurassic terrestrial fossils and paleoecological information.
• Architectural/industrial aspects: some sandstones serve as local building stone and some units contain mineral resources studied by geologists.
• Stratigraphic character: the formation sits above older, often marine or marginal marine rocks and is overlain by younger Cretaceous deposits in many areas.

Together, the Morrison's varied rocks and exceptional fossil record make it a key formation for understanding North American landscapes and life near the end of the Jurassic. For more detailed maps, stratigraphic charts and specimen records see resources linked here: age overview, lithology, distribution maps, dinosaur lists, regional summaries, mudstone data, sandstone data, siltstone data, limestone occurrences, fossil catalogs, depositional studies, Jurassic context.