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eglandulosus, Uva-ursi tomentosa, and, in the San Bernardino 
Mountains, Uva-urst pungens, are perhaps the most characteristic. 
Pseudotsuga macrocarpa grows with these species, especially on 
the north slopes. This tree becomes more abundant at higher 
altitudes and extends into the lower part of the Transition Zone. 
In the canyons, Quercus chrysolepis, Acer macrophyllum and 
Umbellularia californica seldom descend lower than 750 meters; 
but Alnus rhombifolia often follows living streams into the 
edges of the valleys. Platanus racemosa is mostly confined to 
the lower altitudes, and occurs on the canyon floors, often following 
the washes well out into the valleys. 
The following trees and shrubs are mainly restricted to the 
Interior Sub-district: 
Pseudotsuga macrocarpa Ceanothus crassifolius 
Ribes indecorum Uva-ursi pungens 
Adenostoma sparstfolium Trichostema Parishit 
X ylothermia montana tomentosa Pentstemon ternatus 
Lupinus Halli Pentstemon antirrhinoides 
Ceanothus divaricatus eglandulosus Ericameria Parishii 
Desert slopes —The Upper Sonoran Area on the desert slopes of 
the mountains is commonly called the pifon and juniper belts, 
the two conifers, Pinus monophylla and Juniperus californica 
being the most characteristic species. The pion occurs in the 
upper altitudes of the zone (1200-1800 meters). The juniper, 
on the other hand, occupies the lower altitudes (goo—-1200 meters), 
and along the lower edges of the belt mingles with the yuccas and 
other shrubs characteristic of the Lower Sonoran.? In the Provi- 
dence Mountains Juniperus utahensis replaces Juniperus cali- 
fornica. This is the only locality where this species enters into 
our territory, but in the Panamint Mountains it also. replaces 
Juniperus californica, and extends from there eastward over south- 
ern Nevada and Utah. Each of these species may be considered 
as representing a distinct floral district. 
Several trees and shrubs which belong properly to the Intra- 
montane district penetrate through Tejon Pass and extend in a 
7The juniper belt is retained in the Upper Sonoran with reluctance, for 
over a large part of the belt the associating species are predominantly Lower 
Sonoran. On the coastal slope if we found the juniper at all we should expect 
it in the Upper Sonoran, if it actually belongs in that zone, but instead it 
occurs only in the Lower Sonoran of the interior valleys. 
