13 



3. Physiographic province: The range of 

 Lesquerella humilis lies along the boundary 

 of the Rocky Mountain and Idaho batholith 

 provinces of the Rocky Mountain System (Hunt 

 1974) . 



4. Physiographic and topographic 

 characteristics: The Bitterroot Range 

 escarpment is a fault block at the eastern 

 edge of the Idaho batholith. The latter is a 

 granitic mass which is faintly gneissic in 

 character. 



The populations occur on level to moderately 

 steep slopes at elevations of 2685 to 2925 m 



(8800 to 9590 ft.). The sites are on heights 

 of land between tributary streams of the 

 Bitterroot River within hydrologic unit 

 17010205 of the U.S. Geological Survey 



(1980) . 



5. Edaphic factors: Lesquerella humilis occurs 

 on poorly developed, sandy or stony soils 

 derived from metamorphic bedrock. No 

 analyses of soil characteristics have been 

 done. The St. Mary and St. Joseph massifs 

 consist of high grade metamorphic rocks, 

 mostly gneiss and schist, locally penetrated 

 by granitic rocks (Lackschewitz 1970, 1986; 

 Ross et al. 1955) . Although appearing 

 largely granitic in character, the rocks on 

 St. Mary Peak are slightly reddish-orange in 

 color, and the St. Joseph Peak massif is 

 similarly colored. Lesquerella humilis is 

 restricted to this area, but it is not known 

 whether this restriction is strictly edaphic 

 in nature. 



6. Dependence of this taxon on natural 

 disturbance: Lesquerella humilis is 

 associated with open sites that are exposed 

 to strong winds. Consequently, these sites 

 are sparsely vegetated with little soil 

 development. Steeper sites may also be 

 subject to some disturbance from soil creep 

 or solif luction. 



7. Other unusual physical characteristics: None 

 observed. 



