Discovery of Eocene mammals in the San Juan Basin by Cope in 1874 and subsequent collecting of these faunas are reviewed, as well as the broader outlines of early Cenozoic stratigraphic studies here from Newberry, 1859, to the present time. A review of the stratigraphic nomenclature leads to the conclusion that a Paleocene Nacimiento formation, with the Puerco and Torrejon faunas (not formations), is recognizable but that the overlying formation, commonly but incorrectly called "Wasatch," has had no acceptable name. The new name San Jose'' formation is proposed for the "Wasatch" of authors in the San Juan Basin. In s. Colorado there was nearly continuous deposition through the later Paleocene into the Eocene. In the type region, the San Jose'' has two distinct ciay facies and these contain mammalian faunas also recognizably different in facies. These faunas are all Wasatchian and probably extend over the early and middle parts of that age, rather than the middle and later parts as commonly supposed. The Tiffany fauna of s. Colorado, well known to be of late Paleocene age, is in beds not now separated from the San Jose but probably separable and only tentatively assigned to that formation.