We exploited an elevation (climate) gradient ranging from 1,700 to 2,500 m in Poudre Canyon of Larimer County, CO, to determine climatic correlates of abundance per 15-s drag sampling time unit (hereafter referred to as abundance) of the human-biting adult life stage of the Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae), in a key risk habitat for tick exposure: south/west-facing, rocky hillsides with mixed grass–brush–conifer vegetation. The relationship between elevation and abundance was parabolic, with peak tick abundances occurring at mid-range elevations (2,200–2,400 m) and tick abundances approaching zero at ≈2,100 and 2,500 m. Regression modeling demonstrated that abundance of host-seeking adult ticks in south/west-facing exposures was accurately predicted by several climate variables related to temperature (e.g., mean annual minimum temperature, maximum temperature, and base 10°C growing degree-days, and median length of annual freeze-free period; r² values ranging from 0.771 to 0.864), whereas mean annual precipitation, snowfall, or relative humidity were uninformative in this respect (r² values ranging from 0.020 to 0.316). Abundance of D. andersoni adults peaked at a mean annual maximum temperature of ≈10°C and a mean annual growing degree-day value of ≈650. Relationships between climate variables and abundance of D. andersoni adults were used to create geographic information system (GIS)-based models for predicted tick abundance in south/west-facing exposures in Larimer County. This is the first GIS-based model developed for spatial patterns of abundance of D. andersoni. Finally, preliminary data from Poudre Canyon indicate a shift toward peak abundances of D. andersoni adults occurring in sheltered northern/eastern exposures, rather than in drier and hotter southern/western exposures, at elevations below 2,100 m.