( 320) 
In addition to the typical Lower Sonoran species there are a 
number of other shrubby species peculiar to the San Diego region 
which are often the principal components of the chaparral. These 
species are: Cercocarpus minutiflora, Adenostoma fasciculatum ob- 
tusifolium, Ceanothus verrucosus, Xylococcus bicolor, and Coma- 
rostaphylis diversifolia. Pinus Torreyana is also restricted to this, 
with the exception of a small grove on Santa Rosa Island. 
Mohave Desert—The Lower Sonoran Area occupies nearly the 
entire area of the Mohave Desert, only in the upper altitudes of 
the mountains is it replaced by the juniper and pion belts of the 
Upper Sonoran. Wherever the soil conditions are favorable 
Covillea tridentata predominates. This shrub, commonly known 
as the “creosote bush,” is the most characteristic species of the 
entire Lower Sonoran Area, at least in the arid parts; but, on 
account of its wide range and its association in the various regions 
with markedly different floral elements, it cannot be utilized in 
segregating phytogeographical districts. 
Along the upper edges of the Covillea belt, and often extending 
into the edges of the juniper belt, are a number of characteristic 
desert shrubs, such as Grayia spinosa, Tetradymia spinosa, Tetra- 
dymia stenolepis, Amygdalus Fremontii and Adelia neo-mexicana. 
Associated with these is the tree yucca (Cleistoyucca arborescens), 
locally known as the “Joshua tree.”” The great stretches of this 
desert yucca that spread over the gradually sloping plains resemble 
immense orchard tracts, and form a prominent feature of the 
landscape. 
The following Lower Sonoran trees and shrubs have been re- 
corded in the Mohave Desert within the limits of our territory: 
* Ephedra nevadensis * Echinocactus Lecontet 
* Ephedra californica * Echinocactus polycephalus 
* Yucca mohavensis Menodora spinescens 
Cleistoyucca arborescens Adelia neo-mexicana 
* Populus Fremontit Ramona pilosa 
*Salix vallicola Ramona capitata 
*Salix argophylla *Lycium Coopert 
Eriogonum Plumatella Lycium Andersontt 
* Atriplex lentiformis Salazaria mexicana 
* Atriplex polycarpa * Chilopsis linearis 
* Atriplex confertifolia * Hymenoclea Salsola 
Atriplex Parryi Gaertneria eriocentra 
