TOPOGRAPHY 31 



ually toward the valley of the Clark's Fork of the Yellowstone. 

 The canyons in this section are often mere narrow rifts between 

 nearly perpendicular rock walls, which sometimes rise to nearly 

 3000 feet above the floor of the canyon, which here and there 

 is strewn with boulders and glacial debris. 



Toward the west the country decreases in elevation. The 

 lowest canyons are 4000 feet above sea level and from that all 

 elevations occur up to 10,000 the usual elevations of the East 

 and West Boulder Plateaus. Here again glacial action has left 

 its traces, but not of such a character as to indicate that they 

 have been reduced much in height since the ice age began. 

 Through all this region of high peaks there is net a snow cap, 

 so completely is the not too ample snow dissipated by the sum- 

 mer's wind and sun. Some perennial snow fields lie in the lee 

 of high ridges and peaks where the winds have piled the snow 

 too deep for it to disappear entirely during the short summer. 



In this group the Bridger and some lesser ranges form 

 lower plateaus or rounded ridges, forested to the summits, and 

 in outlines far less severe than those of their more lofty neigh- 

 bors. 



In the second area are several groups of mountains which 

 constitute forest islands in the central part of the State. The 

 most western of these, the Big Belt Range, is the only group 

 which is extended in the form of a chain. They lie parallel 

 with the main divide at a distance of 40 to 60 miles for nearly 

 100 miles in a direction from southeast to northwest. Through 

 the intervening valley flows the Missouri River in places through 

 narrow gorges which Lewis and Clark called the Gate of the 

 Mountains. East of the Big Belts are the Little Belts with 

 spurs radiating from a central elevation and supplying the 

 sources of Smith and Judith Rivers and other minor affluents 

 of the Missouri. South of the Little Belts at a distance of 50 

 miles more or less are the Crazy Mountains and east at about 

 the same distance lies the Snowy Range. These several ranges 

 are separated by valleys of greater or less agricultural possibil- 

 ities, and with broad rolling grassy uplands, which gradually 

 merge into sparsely timbered foothills. The higher elevations, 

 in conformity with meteorological conditions, support ample 



