I . INTRODUCTION 



A sensitive plant survey of the Centennial Valley and 

 Mountains was conducted during the summer of 1993. The primary 

 purpose of this investigation was to determine the occurrence, 

 frequency and distribution of the rare plant species considered 

 potentially sensitive by the Bureau of Land Management (BLM) . 

 This inventory of sensitive plants is a management tool for the 

 BLM to revise the draft BLM list of sensitive plants in Montana 

 and to implement a sensitive species program in the Centennial 

 Valley. 



The Centennial Valley has among the highest numbers of rare 

 species of all BLM land areas in Montana. Although there had 

 been no extensive systematic survey of BLM lands prior to this 

 study, thirteen of the thirty-six known state species of concern 

 in the Centennial Valley (Table 1) had been documented on BLM- 

 administered lands at the start of this project based on such 

 studies as represented in Dorn (1968) , Lowry (1979) , Lesica 

 (1985), Schassberger (1988) and Heidel (1993). 



II. STUDY AREA 



The Centennial Mountains form much of the Continental Divide 

 along the border between southwestern Montana and Idaho (Fig 1) . 

 The Centennial Mountains are on of the few ranges in North 

 America that run in an east-west direction. The mountains are 

 bounded on the north by the Centennial Valley and on the south by 

 the Snake River Plains. This area is represented by a wide range 

 of floristic and vegetational diversity including: open 

 sagebrush desert; open, rocky canyons and streambanks ; open, 

 disturbed roadways and trails; dry, open grasslands; seasonally 

 moist, montane coniferous forests; seasonally moist aspen groves; 

 moist stream courses; montane and subalpine meadows and slopes; 

 subalpine and alpine lakes; subalpine and alpine coniferous 

 forests; alpine scree and talus slopes; meadows, grasslands, and 

 windswept ridges; a wide range of wetland habitats including 

 lakes, ponds, wet meadows, marshes, and seepage area; and sand 

 dunes and hills (Lesica, 1984; Lowry, 1979). 



The Centennial Valley is a high elevation (6600 feet) 

 intermontane valley centered on the Red Rock River headwaters. 

 The valley is located between 44^' 31' and 44" 40' latitude and 

 111° 40' and 112° 20' longitude (Figure 1). Centennial Valley is 

 approximately 4 miles long and 7 miles wide, bordered on the 

 northeast by the Gravelly Range and the Snowcrest Mountains to 

 the northwest. The Centennial Mountains are oriented 

 approximately in an east-west direction, forming the southside of 

 Centennial Valley for 40 miles from Monida Pass, Montana to the 

 Henry's Fork of the Snake River in Idaho. Mount Jefferson on the 

 east side of the range is the highest point, reaching an 

 elevation of 10,211 feet (MAPS 1990). 



