Eocene Period, 58-36 million years B.P. A Knightia alta fossil fish in a rectangular matrix. 217 grams, 11 cm (4 1/3 in.). Green River region, Wyoming, USA. Acquired 1980s. Pradi collection, Boston, USA. Seasonally some 58 million years ago, in the Green River region of Wyoming, torrential rains would occur in the mountains. The rain would flow down the mountain sides and then wide shallow lakes would form in the valley below. When the dry season would occur, these lakes would dry up due to evaporation (similar to certain parts of Africa today). Millions of fish would die in this short period of time. This climatic cycle happened over a 20-thousand-year period. Layer upon layer of mud was deposited over these years entombing all these fish. At a much later date volcanic activity uplifted this area to expose all those layers of fossil fish. [No Reserve]