Table I .--Average temperature and precipitation at selected localities in the ponderosa 

 pine forests of the northern Rocky Mountains (U.S. Weather Bureau) 



Average temperatur e : Average precipitation 



T ,or a 1" \ on 



; June 



: July 



: Aug . 



:Sept . : 



Ye ar '. 



J UT16 



: Julv : 



Aug. : 



: Sept . : 



Yc s.r 









Degrees 



F - 







- - Inches - - 







Chewelah, Wash. 



61 



67 



64 



57 



46 



l . l 



0.6 



0.6 



1 . 1 



19 . 8 



Spokane, Wash. 



62 



70 



68 



61 



48 



1.5 



.4 



.4 



. 8 



17.2 



Kalispell, Mont. 



59 



66 



63 



55 



43 



2.2 



1.0 



1 . 1 



1.0 



15.4 



Missoula, Mont. 



58 



67 



64 



54 



43 



1.9 



.8 



. 7 



1.0 



12.8 



Darby, Mont. 



57 



65 



63 



55 



45 



1.9 



.8 



.8 



1.2 



15.7 



Grangeville, Idaho 



58 



67 



66 



58 



46 



3.0 



.9 



. 8 



1.5 



22.6 



New Meadows, Idaho 



56 



63 



60 



53 



41 



2.0 



.6 



.6 



1.2 



25. 3 



Council, Idaho 



63 



73 



70 



62 



48 



1.8 



. 4 



.4 



.9 



26.8 



Idaho City, Idaho 



58 



67 



65 



57 



45 



1.4 



.3 



. 3 



.6 



23.2 



Bryce Canyon, Utah 



59 



63 



60 



48 



40 



0) 



1 . 1 



2.9 



3.4 



12.7 



Less than 0.06 inch. 



In the Intermountain Station territory there are extensive areas of shallow soil 

 with bedrock often close to the surface. These are frequently intermingled with deeper 

 soils on level plateaus and, more generally, on minor ridges and major drainage 

 boundaries. The total acreage of shallow soils is not known, but surveys on two timber 

 sale areas in central Idaho revealed that the proportion is considerable. On 480 acres 

 on the Boise Basin Experimental Forest supporting ponderosa pine, soil was less than 

 24 inches deep in 23 percent of the area. On Zena Creek, a tributary of the South Fork 

 of the Salmon River, Payette National Forest, a soil survey showed 31 percent of the 

 area to have soils only 8 to 16 inches deep on bedrock. 2 



Most commonly, the south and west aspects support shallower soils than the north 

 and east aspects. Soil depth generally decreases, regardless of asnect, toward the 

 top of ridges. The deeper soils occur in the ravine bottoms where the topography tends 

 to be gentle, although exceptions occur on some plateaus as in eastern Utah. Cox and 

 others (1960) point out that in western Montana forest productivity is influenced 

 principally by the depth of soil in which tree roots can develop. 



Shallow soils affect si lvicultural practices (Curtis 1961). For example, certain 

 units may be eliminated from a proposed cutting because soil is not deep enough for 

 adequate site preparation for regeneration or because the potential for erosion or 

 site deterioration following cutting is too great. 



^0. C. Olson. Soils of the Zena Creek logging study, Payette National Forest, 

 Region 4 unpubl. ms., illus. 1960. 



3 



