86 



KORKST 



Tin- sixth section includes the Bitter Root Valley. ;in area 

 of about 3000 square miles. It is hounded on the west hy the 

 summit <!' the Bitter Hoot Mountains and on the southeast it 

 reaches to the crest of the Continental Divide. On the east its 

 margin rests upon the top of the divide between the Bitter Root 

 River and Rock Creek. 



Table 14. The Forests of the Bitter Hoot Section. 



It will be observed that the prevailing species in this sec- 

 tion are those adapted to drier conditions, viz., the yellow and 

 loduepole pines and the Douglas spruce. All others are in a 

 small minority. The species of the humid forests, the white 

 pine and its associates, are now mostly confined to the upper 

 canyons of the Bitter Hoot Kanjre. This conforms exactly to the 

 climatic conditions of the section. The Bitter Hoot Valley has 

 an annual precipitation record of 10.71 inches, representing the 

 average ( ,f a good many years of observation. This is a lower 

 figure than is shown at most of the plains stations in eastern 

 Montana. They are, however, tl bservat ions at only one sta- 

 tion that of Hamilton near the center of the valley. It is easy 

 to understand this condition since the whole valley is sheltered 

 on the west by the lofty Bitter Hoots, which effectually intercept 

 the rain bearing western winds. Tin- temperature of the Bitter 

 Valky is. moreover, usually a little higher than that <f the 

 iH-iirhborini: localities, which must further influence its water 

 supply. 



The lower limits of vertical distribution are considerably 



