Judith River Formation

Judith River Formation
Stratigraphic range: Campanian, 79–75.3 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Judith River Formation, Upper Missouri Breaks National Monument
Type	Geological formation
Unit of	Judith River Group
Sub-units	Parkman Sandstone Member, McClelland Ferry Member, Coal Ridge Member, Woodhawk Member
Underlies	Bearpaw Formation
Overlies	Claggett Formation, Pakowki Formation
Thickness	max 360 meters (1,180 ft)[1]
Lithology
Primary	Mudstone and sandstone
Location
Region	Montana
Country	United States
Type section
Named for	Judith River near the confluence with the Missouri River
Named by	F.V. Hayden, 1871;[2] F.B. Meek, 1876.[3]

The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the Late Cretaceous, between 79 and 75.3 million years ago,^[4] corresponding to the "Judithian" land vertebrate age. It was laid down during the same time period as portions of the Two Medicine Formation of Montana^[5] and the Oldman Formation of Alberta.^[6] It is an historically important formation, explored by early American paleontologists such as Edward Drinker Cope, who named several dinosaurs from scrappy remains found here on his 1876 expedition (such as Monoclonius). Modern work has found nearly complete skeletons of the hadrosaurid Brachylophosaurus.