This species is endemic to a five-county area of west-central Idaho in the United States (Yensen and Sherman 1997). The northern subspecies (brunneus) presently is known only from Valley and Adams counties at elevations of 1,150-1,550 m asl; most populations are small and often isolated by several kilometres (Yensen 1991). The southern subspecies (endemicus) has a patchy distribution at lower elevations (670-975 m asl) north of the Payette River in Gem, Payette, and Washington counties. The species is apparently extirpated in the area between the extant populations of the northern and southern subspecies (Yensen 1984, 1991, Yensen et al. 1991, Yensen and Sherman 1997). Even within subspecies, populations are disjunct.