MESA AND FOOTHILL VEGETATION 49 



are mostly Indian currant. The small lateral ravines on the south slope of Horse Mesa 

 support chiefly a growth of young thorn apple, choke cherry and skunk bush. 



Fig. 3.- — Invasion of grassland by rock pines. The coarseness of the soil is indicated 

 by the numerous boulders. It is in such situations as this that young pines are able to 

 become established while it would be much more difficult in the fine-grained soil of the 

 plains. 



Fig. 4. — The view shows numerous rock pine seedlings getting started along a road 

 on the mesa. Seedlings are common along old road beds and other places where the 

 ground is bare. 



