Wasatchian

The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 55,400,000 to 50,300,000 years BP. It is usually considered to be within the Eocene, more specifically the Early Eocene. The Wasatchian is preceded by the Clarkforkian and followed by the Bridgerian NALMA stages.

The Wasatchian is considered to contain the following substages:
 * Lostcabinian: (shares upper boundary) and lower boundary source of the base of the Wasatchian (approximate).
 * Lysitean: Lower boundary source. Base of Wasatchian (approximate) and upper boundary source of the base of the Bridgerian (approximate).
 * Graybullian: Lower boundary source: base of Wasatchian (approximate) and upper boundary source of the base of the Bridgerian (approximate).
 * Sandcouleean (shares lower boundary) and upper boundary source of the base of the Bridgerian (approximate).