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 difficult for a mounted man to make 
his way among them. This is partly due to the fact that the oaks, the 
juniper, and the pifiion 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 emory? 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 pachyphlea 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 schottit 
is no longer found and Agave palmer, like 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 californica and Quercus oblong- 
tfolia, 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 
flavescens 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 wrightit, Chenopodium fre- 
montit, 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 
