Evanston Formation, Geological formation in southwestern Wyoming, United States
The Evanston Formation is a geological layered sequence in southwestern Wyoming with multiple rock types. It consists of gray siltstone, reddish sandstone, and coal seams spanning across Lincoln and Uinta counties.
This formation developed between about 66 and 59 million years ago during the transition from the Late Cretaceous to the early Paleocene. It formed through sedimentary processes that accumulated thick layers of material during this period.
Researchers from various institutions study this formation to understand the transition between dinosaurs and early mammals through fossil examination. The layers help piece together what life was like during this distant period.
Visitors can see different layers of this geological formation in natural exposures, particularly where erosion has revealed the strata. It is best explored on foot to observe the various rock types and how they are arranged across the landscape.
The formation has preserved a remarkable collection of fossils from a time when larger and smaller animals lived side by side. Among the discoveries are large dinosaurs like Triceratops and Alamosaurus as well as early mammals and primitive primates from a period when both groups shared the earth.
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