90 FOREST DISTRIBUTION 



importance <n the different mountain ranges in this section. 

 Leihen: (32 gives the volume per cent for the different species 

 in tlie Little Kelts as follows: 



Pinus flexilis 8.2 



" <ilhi<-<ii(!i (KM) 



contotia - 34.2 



" ponderosa 07 



ric<(t I^n(/t hniiiuiii 11.4 



Pseudotsuga la.i'ifulia 44.7 



Abies lasiocarpa 1.4 



In addition to the above species it is probable that Ji<ni}>< rii* 

 si-nfuilnrnni and J. cotn munis are likewise present. Isolated as 

 most of the outstanding ranges are, the influence of the climatic 

 conditions are readily felt, so that the lower timber line is fixed 

 at elevations unusually high. In sheltered canyons and valleys, 

 however, many of the species may descend to where they open 

 out upon the plains. 



The Three Forks Section (No. 10) is an area 140 miles from 

 eaM to west and KM) miles in round figures from north to south. 

 The westward direction of the Continental Divide from the vicin- 

 ity of Unite, and its wide curve to the south and thence to the 

 ast to Yellowstone Park forms a huge embayment, drained by 

 the three main sources of the Missouri, the Gallatin, the Madi- 

 son and .Jefferson rivers, which push their ultimate branches 

 to the hiirh walls of this huge amphitheater. The western por- 

 tion of the basin is known as the Bighole, particularly that part 

 drained by the Hiuhole River which is the main western branch 

 of tin- .lefTi-ixdii. The basin is traversed by several low moun- 

 tain ranges. ;ind in altitude most of its floor lies above 5000 feet. 

 The country is largely prairie and only the highest elevations 

 arc forested ;iud these with few speejes and comparat i vely meairi-r 

 L'rowth. It is largely glaciated and climatically dry and cold. 



