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The Green River Formation in southwest Wyoming was a series of three lakes during the Tertiary Period. Lake Uinta, Lake Gousiute and Fossit Lake lay in a series of intermontane basins formed by geologic events that uplifted the Rocky Mountains in the early Tertiary. During the Eocene Epoch, the climate was subtropical and supported flora such as large palm trees and fauna including crocodiles, alligators, boa constrictors and various fish families.Over time these lakes were filled with sediments and ash from volcanic activity in the region. Many fish are found preserved in the successive layers laid down in the lake beds 40 to 60 million years ago. The fish are found singularly or in large groupings referred to as 'mortality layers' which are believed to be the result of extensive ash fall-out after ancient volcanic eruptions. Quarry operators in the fossil beds split flat pieces of limestone hoping to split through layers that contain fossils. Remaining limestone is cleaned away to reveal the bones and skin fragments that were preserved. |
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