Obsidian samples from two locations in the western Great Basin, the northern Fish Lake Valley and the Volcanic Tablelands in northern Owens Valley, were collected and analyzed using Instrumental Neutron Activation Analysis. These locations had not previously been described as sources of obsidian, although they contain small, weathered nodules on the surface. Obsidian from the former provides a chemical signature distinct from all other previously documented sources in the area, while the latter is chemically similar to obsidian from the Mono Glass Mountain area. Variability in Tablelands obsidian sheds light on the distribution and availability of Mono Glass Mountain obsidian and suggests the presence of a distinct subsignature on the Tablelands. The dispersed nature and small size of nodules in both areas probably precluded intensive use, but minor exploitation may have been important in the flaked stone economy of prehistoric inhabitants of the region. Recognizing these sources in regional obsidian studies should help refine models of prehistoric exchange and mobility.