Judith River Formation

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 80 and 75 million years ago, 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 and the Oldman Formation of Alberta.
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 . Modern work has found nearly complete skeletons of the hadrosaurid Brachylophosaurus.

The Judith River Formation is composed of mudstone, siltstone and sandstone. Coal beds, bentonite and coquinas are also observed.

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