Approximately 50 million years ago, the Green River Formation comprised an area of more than 25,000 square miles (65,000 sq. km) of interconnected subtropical lakes spread across the current states of Wyoming, Utah, and Colorado. Today, the region of ๊the Green River Formation known as "Fossil Lake" boasts some of the most abundant and well-preserved freshwater fossils anywhere in the world.

Highlights of this fossil fish plate include the large surface-feeder Diplomystus dentatus, characterized by its distinctive upturned mouth bristling with teeth, two fine examples of the temperate bass species Cockerellites liops, as well as Wyoming's state fossil, the herring-like Knightia eocaena. The included log creates a more comprehensive vision of the flora and fauna that existed during the Early Eocene in what is now tꦛhe American West.