CHAPTER I. 



Topography. 



THE region here under consideration lies mostly between 

 the 45th and 49th parallels of north latitude. Its width 

 from north to south is 276 miles, and, measured west 

 from the 104th meridian it extends 624 miles across the main 

 and secondary ranges of the Rocky ^Mountains. The tctal area 

 is close to 175,000 square miles. This embraces nearly all of 

 the State of ilontana and includes a portion of eastern and 

 northern Idaho. 



The mountain ranges of IMontana have mostly a southeast 

 to northwest direction. They are thus essentially parallel with 

 valleys of greater or less width between, ilost of these inter- 

 mountain valleys have in width from two to twenty miles of 

 river bottom and bench land, mostly the latter, which ascends 

 gradually or abruptly into foothills, behind which rise ri^gged 

 mountains, dissected by numerous strong tributaries of the main 

 streams. The valleys proper are, but narrow strips as a rule in 

 the broad drainage basins of which they form a part. 



The mountains and valleys have been formed by successive 

 faulting and tilting on a grand scale. The eastern slope of a 

 range usually represents its fault face (7), the western slope 

 inclines more gradually to the foot of the next abrupt ascent. 

 Only two great mountain chains, however, figure conspicuousl.v 

 as barriers in the spread of the flora of the state, the others are 

 of subordinate or negligible importance. One of these is 

 the Bitter Root ^Mountains and those shorter ranges to the north- 

 west in the same general alignment, the other is the Continental 

 Divide. 



The eastern border of ^lontana on the ^lissouri lies 189S feet 

 above sea level. Prom this point the laud gradually rises to 

 the summit 400 miles to the west and drops down again to about 

 1800 feet where the Kootenai River crosses the western boundarv 

 of ilontana, the lowest point in the State. The altitude of half 

 the State or more is above 3000 feet. The highest point is 



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