Fish Fossils

The various fossil beds of the Green River Formation span a 5 million year period, dating to between 53.5 and 48.5 million years old. This span of time includes the transition between the moist early Eocene climate and the slightly drier mid-Eocene. Rocks of the Green River Formation contain a story of what the environment was like about 50 million years ago in what is now parts of Colorado, Utah, and Wyoming. At that time, forces within the Earth were almost finished with the job of uplifting the Rocky Mountains, and the landscape consisted of rugged mountains separated by broad intermountain basins.