28 VEGETATION OF A DESERT MOUNTAIN RANGE. 



The heaviest stands of the Upper Encinal constitute a relatively- 

 dense thicket in which the trees are from 18 to 30 feet in height and 

 so closely placed that it is very diflScult for a mounted man to make 

 his way among them. This is partly due to the fact that the oaks, the 

 juniper, and the pinion all branch freely from a point near the ground, 

 and partly to the size and hemispherical habit- of Arctostaphylos, in 

 which many of the stiff branches are placed in a nearly horizontal 

 position near the ground. These dense stands of the Upper Encinal, 

 between 5,600 and 6,200 feet, are made up of the same species that 

 form the very open Lower Encinal in so far as concerns the trees, shrubs 

 and larger perennials. There are, however, many root-perennial her- 

 baceous plants in the Upper Encinal which are not to be found below 

 5,500 feet, nearly all of which extend upward into the lower portions 

 of the Forest region. 



Quercus emoryi is still a common tree at 5,600 feet, Quercus arizonica 

 is replaced by the closely similar Quercus reticulata, Quercus hypoleuca 

 makes its first appearance, and Juniperus pachyphlcea and Pinus cem- 

 broides reach their maximum abundance between 5,500 and 6,500 feet. 

 Dasylirion, Nolina, and Yucca are still conspicuous elements of the 

 vegetation even in the most dense stands of oaks, but Agave schottii 

 is no longer found and Agave palmeri, Hke the cacti, is found only on 

 ridges and rocks. A common tree of the lower forest region. Arbutus 

 arizonica, is first found in the Upper Encinal, where its isolated indi- 

 viduals are conspicuously different from the oaks. The only trees of the 

 mountain, excepting the desert species, the ranges of which lie wholly 

 below the Upper Encinal, are Vauquelinia calif ornica and Quercus oblong- 

 ifolia, while Quercus arizonica reaches its upper limit in this region. 



Phoradendron californicum, the mistletoe, which so commonly infests 

 Prosopis and the other trees of the desert, is found throughout the 

 Desert region of the mountains, while in the Encinal Phoradendron 

 fiavescens var. villosum is found on several hosts and Phoradendron 

 juniperinum is extremely common on Juniperus, but does not extend 

 with it to its highest occurrences. 



The vegetation of the Upper Encinal is extremely poor in shrubs 

 of the type so common in the Upper Desert and still frequent in 

 the Lower Encinal. In the open spots there may be found a few 

 individuals of Artemisia ludoviciana, Parosela wislizeni, Anisolotus 

 argensis, and other dwarf shrubs of the Lower Encinal, while in the 

 shade of the heaviest stands of oaks are to be seen Pteris aquilina var. 

 pubescens, Muhlenbergia affinis, Polygala alba, Comandra pallida, 

 Hymenopappus mexicanus, Cordylanthus wrightii, Chenopodium fre- 

 montii, and other species of root-perennials. The vegetation of rocks 

 and exposed ridges is still suggestive of the desert, both in its physiog- 

 nomy and in its phyletic relationships. In the crevices of rocks, where 

 the amount of soil is extremely scant and the supply of moisture must 



