Of, relating to, or designating an interglacial stage of the early Pleistocene in North America, between the Nebraskan and Kansan glaciations.
It is now thought that the identification of the Nebraskan, Aftonian, and Kansan stages was based on an incorrect analysis of glacial and interglacial deposits, and the names are becoming superseded by the inclusive term ‘Pre-Illinoian’.
With the. The Aftonian interglacial or its deposits.
Late 19th century. From Afton, the name of a town in Iowa, U.S.A., where an exposure of these deposits was found + -ian.