38 POREST nisTKMiii TION 



indicate tlint some of the stivams it flood may attain more than 

 inoo times their low water volume, hut more often the increase 

 is about 120 to 30 fold. 



The tributary valleys of western Montana mostly have a 

 north and south direction and occupy trench-like depressions 

 between hiuh ranges. The valleys are often or even usually 

 narrow, but occasionally broaden out into numerous inter- 

 niountain basins, as some parts of the Flat head and the upper 

 Blackfoot Valley. Some are the basins of old lakes with the 

 evidence of their ancient shore lines still intact. The positions 

 of the ranges and their alternating valleys in most cases is 

 squarely across the lines of eastward or westward movement. 



