Green River Formation

The Green River Formation is an Eocene geologic formation that records the sedimentation in a series of intermontane lakes. The sedimentary layers were formed in a large area of interconnecting lakes, named for the present-day Green River, a tributary of the Colorado River. The area of the formation exists as three separate basins around the Uinta Mountains of northeastern Utah: an area in northwestern Colorado east of the Uintas, a larger area in the southwest corner of Wyoming just north of the Uintas known as Lake Gosiute, and the largest area, which lies in northeastern Utah and western Colorado south of the Uintas, known as Lake Uinta. Fossil Butte National Monument in Lincoln County, Wyoming is located in a part of the formation known as Fossil Lake because of the abundance of exceptionally well preserved fish fossils found in the area.
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