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The Goler Formation is the only rock unit on the West Coast of North America that has yielded a diverse assemblage of Paleocene vertebrates. Intense prospecting of strata representing member 4 of the formation over the past two decades has resulted in recovery of over 70 specimens of eutherian mammals, representing 18 species. All specimens were recovered from member 4a and the lower part of member 4b, except an isolated tooth referred to Phenacodus cf. P. vortmani from member 4d in the uppermost part of the formation. Three taxa are new, the plesiadapid, Nannodectes lynasi, and two hyopsodontid condylarths, Promioclaenus walshi and Protoselene ashtoni. Also present are four species of Phenacodus, two species of Protictis, and single species representing Goleroconus, Mimotricentes, Lambertocyon, Ignacius, Paromomys, Bessoecetor, Thryptacodon, Dissacus, and a taeniodont. The mammalian fauna from member 4a and the lower part of member 4b is collectively referred to as the Goler Assemblage because taxa recovered from sites throughout this 500 m stratigraphic interval are too similar to subdivide into discrete biostratigraphic units. Based on comparison to faunas from well-known Tiffanian sites in the Western Interior, the Goler Assemblage is probably middle Tiffanian (Ti3–Ti4a), although a Ti5a age is also possible. The Goler Assemblage exhibits significant endemism as 40% of its taxa are not reported elsewhere and only four of 18 Goler Assemblage eutherians can be confidently referred to known species. Comparison to seven Ti3–Ti4a aged sites from the Western Interior indicates that the Goler Assemblage has a closer affinity to more southern faunas (southern Wyoming, Colorado, and Texas), than northern faunas (northern Wyoming, North Dakota, and western Canada), and is most similar to the mammalian assemblage from the Ledge Locality in the Bison Basin of southern Wyoming. Presence of late Paleocene—early Eocene marine strata in the uppermost member of the Goler Formation indicates that the Goler Basin was probably adjacent to the Pacific Ocean during most of its existence. Also, significant distances and one or more paleodrainage divides separated the Goler Basin from Western Interior basins, factors that limited the dispersal of mammals between the West Coast and the continental interior and contributed to the formation of a discrete faunal province on the West Coast of North America during the late Paleocene.