Morrison Formation

Morrison Formation
Stratigraphic range: Upper Jurassic (Kimmeridgian to Tithonian), 156.3–146.8 Ma PreꞒ Ꞓ O S D C P T J K Pg N
The distinctive banding of the Morrison Formation, a group of rock layers that occur throughout Dinosaur National Monument and the source of fossils like those found at the Dinosaur Quarry
Type	Geologic formation
Underlies	Cedar Mountain Formation, Cloverly Formation, Lakota Formation, Burro Canyon Formation
Overlies	Summerville Formation, Beclabito Formation, Curtis Formation, Bell Ranch Formation, Sundance Formation
Thickness	Up to 200 m
Lithology
Primary	Mudstone
Other	Sandstone, siltstone, limestone
Location
Coordinates	39°39′04″N 105°11′17″W / 39.651°N 105.188°W / 39.651; -105.188
Approximate paleocoordinates	40°24′N 53°12′W / 40.4°N 53.2°W / 40.4; -53.2
Region	Central North America:  Arizona  Colorado  Idaho  Kansas  Montana  Nebraska  New Mexico  North Dakota  Oklahoma  South Dakota  Texas  Utah  Wyoming
Country	United States[1]
Extent
Type section
Named for	Morrison, Colorado

The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone, and limestone and is light gray, greenish gray, or red. Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period.

It is centered in Wyoming and Colorado, with outcrops in Montana, North Dakota, South Dakota, Nebraska, Kansas, the panhandles of Oklahoma and Texas, New Mexico, Arizona, Utah, and Idaho. Equivalent rocks under different names are found in Canada.^[2] It covers an area of 1.5 million square kilometers (600,000 square miles), although only a tiny fraction is exposed and accessible to geologists and paleontologists. Over 75% is still buried under the prairie to the east, and much of its western paleogeographic extent was eroded during exhumation of the Rocky Mountains.

It was named after Morrison, Colorado, where some of the first fossils in the formation were discovered by Arthur Lakes in 1877. That same year, it became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope. In Colorado, New Mexico, and Utah, the Morrison Formation was a major source of uranium ore.