VEGETATION OF THE SANTA CATALINA MOUNTAINS. 23 
yos on the bajada, is found here growing with Parkinsonia microphylla, 
which it eventually exceeds in vertical distribution by nearly 500 feet 
(153 m.). Prosopis is even more abundant at 4,000 feet (1,220 m.) 
than it is on the lowest slopes, and attains a trunk circumference of 
6 feet (2 m.) at 4,200 feet elevation (1,280 m.), within 600 vertical 
feet (183 m.) of its upper limit. Such common shrubs of the bajada 
as Lycium, Zizyphus, Krameria, Jatropha, and Momisia are now very 
sporadic in their occurrence, and the compact, hemispherical and 
vividly green Chrysoma laricifolia has become very frequent and con- 
spicuous, together with the white-tomentose Artemisia ludoviciana and 
the less conspicuous Eriogonum wrightii. 
On northerly slopes, just below 4,000 feet (1,220 m.), are encountered 
the first individuals of the rosaceous tree Vauquelinia californica and 
of Agave palmeri and Dasylirion wheeleri (sotol). Along the arroyos 
the most conspicuous forms are Erythrina flabelliformis, the large leaves 
and brilliant scarlet flowers of which recall its tropical congeners, 
Manihot carthaginensis, with leaves of striking form, and Ingenhousia 
triloba (wild cotton), with tripartite leaves and large white flowers 
which strikingly resemble those of the cotton plant. 
THE UPPER DESERT SLOPES. 
The slopes lying between 4,000 and 4,500 feet (1,220 and 1,372 m.) 
constitute the upper edge of the desert. On these slopes all the char- 
acteristic species of the bajada are confined to southerly slopes, and 
all but half a dozen of them find their uppermost limits. On the Upper 
Desert slopes Vauquelinia becomes common, although confined to 
ledges of rock, and Juniperus pachyphlea, Quercus oblongifolia, and 
Quercus arizonica occur for the first time away from cafions. On the 
northerly slopes, where these trees form the lowest attenuated edge of 
the Encinal region, Dasylirion occurs in abundance together with the 
lowest individuals of Nolina microcarpa (bear grass), Arctostaphylos 
pungens (manzanita), Agave schottii, and Yucca macrocarpa. 
The physiognomy of the Upper Desert slopes is made distinctive 
from that of the Lower Desert slopes not only by the entrance of these 
plants of striking form, and the exit of the desert species, but also by 
the abundance of perennial grasses, root-perennials, and small shrubs, 
which combine with the ephemeral plants, or their dead remains, to give 
a much more complete ground cover than is to be found in any part of 
the bajadas. The compact and extended patches of Agave schottit are an 
important element in this low cover, and so are the scattered plants of 
Boutelouarothrockii and the bunches of Boutelouacurtipendula, Bouteloua 
oligostachya, Muhlenbergia dumosa, Andropogon scopartum, Eragrostis 
lugens, and Heteropogon contortus (see plates 8 and 9). 
Commonest among the low shrubs and other perennials of the Upper 
Desert are: Chrysoma laricifolia, Acacia suffrutescens, Eriogonum 
