doubtless due in large part, to the 3. eel: of sunlight, for the 

 species persists on very steep slopes the. tf ace the sun. A 

 concrete example of the effect of exposure is found on the ridge 

 "between Hughes Creel: and the west Tori: of Hughes Creel:. Here 

 yellow pine extends to the top of the ridge, occurring on very 

 steep, dry ground, facing sotith. It "becomes more dense ancT 

 vigorous on the moderate slopes near the top. Yellow pine is 

 absent from the steeper part of the northern side of the same 

 ridge and is not important on any part of this exposure. 

 SOIL 



Mr. Girhreath describes the I' ores t in general as a 

 sea of eruptive roclrs with "islands" of sec" imentary character . 

 He observes the. t yellow pine follows 'one eruptive formations 

 while Douglas fir is most successful on water-laid roclrs. 

 He cites the remarlra"ble isolation of areas of yellow pine on 

 Silver and Porphyry Creelrc at high elevations, in a region V7here 

 the general geologic: 1 character ia reversed; i.e. where erup- 

 tive rocks occur in the small "islands" of the watersheds rjust 

 named. Yellow -?ine occinies these eruptive islrrnds. iDhe 

 neighboring region is made up of Douglas fir and loclgepole stands 

 with c onsi derail e grass areas. 



It is quite prohaole that the loose tesrfcure of vol- 

 canic soils, favoring rapid drying', is of greater importance 

 than chemical differences in affecting forest composition. 



