Clarkforkian

The Clarkforkian 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 56,800,000 to 55,400,000 years BP. It is usually considered to be within the Paleocene, more specifically the Late Paleocene. The Clarkforkian is preceded by the Tiffanian and followed by the Wasatchian NALMA stages.

The Clarkforkian shares its upper boundary with the Thanetian and is considered to contain the following substages:
 * Cf3: (shares the upper boundary) and lower boundary source of the base of Clarkforkian (approximate) and upper boundary source of the base of the Ypresian (approximate).
 * Cf2: Is the lower boundary source of the base of the Clarkforkian (approximate)
 * Cf1: Upper boundary source of the base of the Ypresian (approximate)