The fish fossils are found in an area called Fossil Lake, which is a part of the Green River Formation, the world’s largest fossil fish find. This ancient lake was located near erupting volcanoes. The fish are between 40 million and 50 million years old. There are many theories that may explain why these fish died by the thousands in these particular layers. These theories include poisonous volcanic gases, temperature fluctuations, and food shortages. The fish are found in limestone.
This fossil requires special care - exposure to water and other chemicals, such as cleaning products or aerosols, will damage it over time. If you polish the stone, use a dry cloth only, or an air duster that does not contain any disinfectant or other chemicals.