Taxonomic history
Originally described 1873 as single species, Blue Grouse, with 8 subspecies in two groups “Dusky” (D. o. obscurus, D. o. richardsonii, D. o. oreinus and D. o. pallidus : Rocky Mountain and Great Basin ranges from Arizona and New Mexico north to Yukon and Northwest Territories). And “Sooty” D. o. fuliginosus, D. o. sierrae, D. o. sitkensis and D. o. howardi : Sierra Nevada, Cascade Mountains, and coastal ranges to southeast Alaska)
“The groups were split into two species, D. obscurus and D. fuliginosus (AOU 1931), but subsequently reunited by Peters (1934) and the AOU (1944). These taxonomic actions were controversial …... The literature (Munro & Cowan 1947; Jewett et al . 1953) cited as providing justification for lumping sooty and dusky grouse (e.g. Mayr & Short 1970) did not include any of the quantitative description and analysis that has come to be expected for avian contact zones (e.g. Rising 1983).  Rather, species accounts for blue grouse refer only to the existence of a few intermediate specimens from a small number of localities in the mountains of north-central Washington and south-central British Columbia (Pitelka 1941; Munro & Cowan 1947; Aldrich 1963). Thus, the species status of blue grouse has not been resolved.” (Barrowclough et al 2004)
Current re-organization reverts to 1931 classification with subspecies groups from original description comprising a coastal species Sooty Grouse Dendragapus fuliginosus and an inland species Dusky Grouse Dendragapus obscurus. There is a geographically small (relative to entire range ) area of interbreeding in central WA and south-central British Columbia in the Okanagan Valley.