34 



UNIVERSITY OF COLORADO STUDIES 



Pinus scopulorum :• 



Pseudotsuga mucronata *<! 



Fig. i. — Distribution of Rock Pine and Douglas Spruce. — The dots in the 

 map show the relative frequency of the pines, except in the case of the scattered trees on 

 the east end where individual trees are shown. The more dense growth of trees along 

 the north crests of the mesas is especially noticeable. The south slopes are almost devoid 

 of trees while on the north there is a considerable growth. The trees extend out farther 

 on the north slopes than on the south slopes. The scattered trees shown growing toward 

 the mesa ends are in every case young trees which are invading the grassland. Young 

 trees are also found growing all over the mesas among the older trees. These older 

 trees are more common on the upper part of the mesa top and along the north crests 

 out to a point about half-way to the end of the mesa. On the north slopes the pines are 

 found on the drier parts where the soil is rockier and more devoid of grass. Douglas 

 Spruce grows only in the deeper and moister parts of Bluebell and Pole Canyons, on the 

 north exposures. Cemetery Gulch does not furnish enough shade and moisture for a 

 growth of this tree. 



