STUDY AREAS 



This study was designed to fill major geographic gaps in the picture of botanical diversity at the 

 south end of the Butte District, with particular emphasis on the Dillon Resource Area. The three 

 study areas were identified using available biological information and also by consultation with 

 Bureau of Land Management personnel in the Dillon and Headwaters Resource Areas. These 

 areas had not previously been systematically surveyed for sensitive plant species but were 

 considered as having high potential for sensitive plant species. Areas include: the Big Hole 

 Study Area west of Twin Bridges, the Grasshopper Study Area west of Dillon, and the Upper 

 Madison Valley study area south of Ennis (Figure 1). A fourth area around Sage Creek was 

 surveyed during the same time and reported separately (Lesica and Vanderhorst 1995). All areas 

 are located mainly within Beaverhead County, but also to a lesser extent in Madison County and 

 in a comer of Silver Bow County. 



The three BLM study areas treated in this report are in low elevation settings of intennontane 

 valleys or foothills, and they constitute the largest share of public land in these settings. They are 

 administered not as discrete management units but as allotments and other project units. The 

 names used to refer to the separate study areas are strictly for the purpose of distinguishing them 

 in this report. 



Climate of all three areas is semi-arid. The closest weather stations are in Dillon at 5218 ft., and 

 in Ennis at 4953 ft. Mean monthly temperatures in Dillon for January and July are 20.2° F and 

 66.4° F, respectively; mean annual precipitation is 9.6 inches (NOAA 1982). Mean monthly 

 temperatures in Ennis for January and July are 22.6° F and 64.7° F, respectively; mean annual 

 precipitation is 11. 5 inches (NOAA 1982). At both stations, May and June are the wettest 

 months. 



The study areas are within an area of the state possessing an exceptionally di\'erse flora and 

 relatively high levels of vascular plant endemism (Lesica et al. 1984). The endemic species are 

 referred to as either state endemics found only in southwestern Montana, or as regional endemics 

 found also in immediately adjoining areas of neighboring states. The rest of the southwestern 

 Montana flora is made up of many species with biogeographic affinities that include the common 

 Northern Rocky Mountain and the Great Plains elements, as well as Great Basin, Southern 

 Rocky Mountain, Snake River Plain, and Columbia Plateau species. Many are arid climate 

 species favored by the combination of soil, climate, and location features unique to Montana. 

 Thus, the presence of species which are at the margins of their ranges is also high, and the 

 majority of the Montana Species of Special Concern from this area are made up of taxa wliich are 

 peripheral in the state. 



All of the three present study area units are known to harbor sensitive species, but they had not 

 previously been systematically surveyed. Botanical status survey studies conducted in or near 

 the four study areas have provided single-species baselines, including sur\'eys tor Arabisfecunda 

 (Lesica 1985, 1993, Schassberger 1988, \990) Astragalus scaphoides {Lesica \984), Lesquerella 



