The Wasatch Formation is a widespread Early Eocene rock unit across parts of Idaho, Montana, Wyoming, Utah, and western Colorado, first named by Ferdinand Vandeveer Hayden in 1873. Deposited in rivers, floodplains, and lakes, it consists mainly of sandstone, siltstone, mudstone, and shale, with some coal and lignite beds. It is among the western United States’ most important fossil-bearing formations, preserving diverse mammals, birds, reptiles, fish, plants, invertebrates, and trace fossils. Especially significant is its record of the Wasatchian interval, when major mammal groups such as euprimates, perissodactyls, and artiodactyls first appeared, while also preserving evidence of warm climates, shifting landscapes, tectonic activity, and valuable energy resources.