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m 



Figure 4. — From the high forests along the Ritterrool Mountains the country slopes vceslv:ard to a rolling prairie which sweeps into II ashtngton and Oregon. 

 This prairie is, in general, highly productive and given over to grain and pea farming. In this tieic, taken in the heart of the famous Palouse country, the 

 outer flank of the forest, a bell of ponderosa pine, is discerniile in the background. Moscow is in the upper center. (Courtesy of 4lsl Division .Iriation, 

 IVashington Sational Guard.) 



several broad valleys which were originally almost com- 

 pletely forested but which now contain a considerable area 

 of land cleared for agricultural use. The rivers of northern 

 Idaho all drain into the Columbia. 



A close relationship between elevation and climate is 

 indicated by the available data. The average precipita- 

 tion at each of five weather stations scattered through the 

 mountainous territory varies between .^2 anti 4'> inches per 

 year,' but most of these stations are in valleys, whereas 

 the heaviest fall of rain and snow occurs on the slopes 

 above. .Along the high eastern bounilarv of northern 

 Idaho the average annual precipitation is probal>ly well 

 above 40 inches, but by contrast, at seven jxiints m or 

 bordering the prairie section it is only about 25 inches. 

 There are also differences in temperature, the prairie 

 stations averaging somewhat warmer than the valley and 

 slope stations during all seasi)ns. In general, the weather 

 in northern Idaho is hot and drv in the summer and 



' Hak;, I. T., Davis, K. P., ami Wkioman, R. H. nafirai. rk- 

 i;bnerai'ION in the western white imne tyi-e. V. S. Dept. .Vgr. 

 Tech. Bui. 767, 99 pp., illus. 1941. 



relatively ct)l(.l in the winter when most ot the precipitation 

 occurs. 



The effects of climate and topography are directly 

 apparent in the natural vegetation. Proceeding westward 

 from the higher elevatitins in that portion of the area lying 

 north of the Clearwater River, the vegetative cover changes 

 from subalpine forest stands to stands of western white 

 pine and associated species, to ponderosa pine stands, and 

 finally to grassland (see colore*.! map at end of report). 

 S<iuth of the Clearwater River is a similar graiiation ot 

 forest types from the high. nu>ist, and cih>I back, country 

 to the lower, drier, and warmer prairie lanvis (fig. 4\ 

 but here the western white pine is ot only ivcasional 

 occurrence. 



Northern Idaho, although only about one-fourth of the 

 State, incluiles 12.5 million acres of land area or U',5tX^ 

 square miles a greater area than New Hampshire and 

 N'ermont combineil. Ol this, 83 {X-rcent is torcst land 

 and 1~ }">erccnt nonforest (table 1). Most ot the non- 

 forest area is improvcil farm land and natural grassland 

 tound mainly along the western margin. Cleared tartn 



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