1907] YOUNG 



ORADO 337 



t 



I 



Water content 



I5cni jy_^^cm 



Station x\.^ (June 26) 43.7 per cent. 14.6 per cent. 



Station B.* (June 26) 30.0 per cent. 



Station C.f (July 30) 21 . 2 per cent, 



* Observations made tollowing a period of showery weather. 

 t Rain two days previous. 



. (3) THE PINUS-SCOPULORUM PORMATION {fig, 2) 



This formation covers the dry slopes of the mountains from their 

 base at an altitude of 1650"^ to about 2400"^. It is exceedingly 

 open, the pines seldom exercising any decided control on the sur- 

 rounding vegetation, except when associated with the Douglas firs. 

 While the Pseudotsuga characteristic of the Pseudotsuga-Picea for- 

 mation extensively overlaps the Pinus scopulorum formation, I have 

 thought best to consider the two as distinct, because the character- 

 istic habitat of each is distinctly different. Pseudotsuga, in the lower 

 part of its range, is restricted to the north slopes and the canon 

 bottoms, while Pinus scopulorum occurs indifferently over north and 

 south slopes alike, and is absent from the cool, moist canon bottoms 

 (see below). Pinus scopulorum is frequently associated in more or 

 less dense clumps with Pseudotsuga, and where such is the case, or 

 where the pines themselves grow densely, there is present no under 

 layer whatever, with the exception of a few mosses and lichens. As 

 soon as the formation becomes thinned out a little, shrubs and grasses 



w 



from neighboring areas wander in. Sahina scopulorum is found in 

 scattered association with the pines throughout the formation. 



According to old residents of the county, the pines were formerly 

 much more numerous than at present, having been largely cut for 

 timber, this species having been formerly the principal timber tree 

 of the mountains. At present comparatively little is being cut. The 

 formation is in a dynamic condition. Large numbers of pine saplings 

 are springing up throughout its extent, and on the mesas, which 

 extend peninsula -like from the mountains on to the plains, are numer- 

 ous strips of open pine forest, gradually invadingjhe grass land of 

 the plains.^ An exposed sandstone cliff 11^°" from the base of the 



5 Ramaley {op. clt.y p. 31) explains the presence of trees on the west end of the 

 mesas and their absence on the east end by a difference in moisture between the two. 

 Since the pines grow on exposed south slopes of the mountains, however, where the 

 water content is very low, this explanation does not appear to me fully satisfactory. 



