New geological mapping near Anvil Lake in the west central part of the Tay River map sheet, south-central Yukon, has highlighted unrecognized stratigraphy within, and re-defined the extent of, Devono-Mississippian formations. Previously mapped Cambro-Ordovician rocks have been newly assigned to the Earn Group based on micro- and macro-fossil data and U-Pb geochronology. The lowermost part of the Earn Group in this area is made up of black chert and recessive shale with rare fossiliferous lenses that yield late early to early Middle Devonian macro-fossils. Sitting conformably above these rocks are coarse sandstone and conglomerate interlayered with siltstone and shale and intermediate volcanic rocks. The latter are andesite flows and crystal tuffs both of which have U-Pb ID-TIMS ages that range from 363-365 Ma. The uppermost part of the Earn Group in this area comprises a succession dominated by fine grained, quartz-rich clastic rocks with lesser limestone that contain Upper Devonian to Lower Mississippian conodonts and radiolarians. Our new detailed mapping and age constraints are improving the stratigraphic knowledge of Devono-Mississippian successions and providing the basis for regional correlation and paleogeographic analysis.