20 



classified as cool and dry, with locally 

 greater amounts of precipitation in the 

 mountains; there are numerous summer 

 thunderstorms. For the distributional 

 area of P. lemhiensis in Montana, the 

 nearest, climatological stations are 

 located' in Darby (1180 m (3880 ft.)), 

 Dillon (1590 m (5215 ft.)), and Wisdom 

 (1850 m (6068 ft.)). Data for the period 

 1951-1980 are provided by the U.S. 

 Department of Commerce (1982) . At Darby, 

 the mean annual precipitation was 40.11 cm 

 (15.79 in.); the mean annual temperature 

 was 7.44°C (45.4°F), and the mean July 

 maximum temperature was 28.83°C (83.9°F). 

 At Dillon, the mean annual precipitation 

 was 24.21 cm (9.53 in.); the mean annual 

 temperature was 5.9'C (42. 6* F), and the 

 mean July maximum temperature was 2 8.5°C 

 (83.3'F). At Wisdom, the mean annual 

 precipitation was 29.06 cm (11.44 in.); 

 the mean annual temperature was 1.7'C 

 (35.1*F), and the mean July maximum 

 temperature was 25.7'C (78.2'F). 



c. Local microclimate: Penstemon lemhiensis 

 generally occurs on open slopes with east 

 to southwest exposures. These sites are 

 likely to have comparatively warm 

 microclimates . 



2. Air and water quality requirements: Unknown. 



3. Physiographic province: The range of P. 

 lemhiensis lies in the Rocky Mountains and 

 Idaho batholith provinces, within the Rocky 

 Mountain System, as mapped by Hunt (1974) . 



4. Physiographic and topographic characteristics: 

 The geologic structure of southwestern Montana 

 is highly complex, consisting of many types of 

 sedimentary and igneous rocks. The major 

 formations with which P. lemhiensis is 

 associated include the intrusive granitic rocks 

 of the Idaho batholith, Cenozoic Tertiary 

 sediments of the Willow Creek formation, the 

 Precambrian Upper Belt formations of the Piegan 

 and Missoula groups, and the Paleozoic 

 Mississippian, Pennsylvanian, and Permian 

 formations (Perry 1962) . 



The Big Hole Basin appears to be underlain by 

 Tertiary lake beds; these beds are generally 



