VEGETATION OF THE SANTA CATALINA MOUNTAINS. 11 
truncated at its lower edge by the Rillito, which flows at right angles 
to the slope of the bajada, and on the western side of the range the 
Cafiada del Oro has worn off the lower edges of the detrital slopes in 
similar matter. The well-developed bajadas which lie between Pima 
and Ventana Cajfions fall at the grade of 150 to 175 feet per mile. 
Between Ventana and Bear Cafions the uppermost portion of the 
bajada has been worn away, so that at present a shallow valley lies 
between the hase of the mountain and the lower portion of the old 
bajada, now cut into isolated and rounded hills. On the northeast 
side of the Santa Catalinas the bajada which extends down to the San 
Pedro River exhibits approximately the same grade as the bajada at 
Pima Cafion. Its surface is crossed, however, by so many drainages 
from the steep northeast face of the mountain that the bajada region 
consists of a series of rounded ridges extending out from the base of 
the mountain, very unlike the relatively flat bajadas of the Santa Rita 
and El Rincon ranges. 
VEGETATION OF THE SANTA CATALINA MOUNTAINS. 
The journey from the base to the summit of the Santa Catalina 
Mountains brings to the eyes of the observer a constantly changing 
panorama of vegetation. New types of plants are constantly being 
encountered with increase of altitude, while types already familiar are 
being left behind. There is no portion of the mountain, at least below 
7,500 feet, in which a climb of 500 feet does not materially alter the 
physiognomy of the surrounding vegetation. The course of the vege- 
tational panorama is not merely a gradual transition from the open 
desert of succulents and microphylls to the heavy fir forest which 
occupies the summit of Mount Lemmon (plate 1). There are inter- 
posed between these vegetations two distinct belts of plant life through 
which this tremendous transition takes place. 
The arborescent cacti and the trees and shrubs of the desert give 
way gradually to evergreen oaks, leaf-succulents, sclerophyllous shrubs, 
and perennial grasses. This open but arborescent vegetation reaches 
a full development and then gives way to pine forest, with a distinctive 
accompanying carpet of herbaceous perennials. The pine forest is 
then, in turn, invaded by spruce and fir and the heavy stands of these 
trees are accompanied by still another assemblage of shrubs and her- 
baceous plants. The striking character of these gradations of vegeta- 
tion is not due solely to the contrast between the varied vegetation 
of the open desert and the monotony of the closed coniferous forests, 
but is quite as largely due to the striking types of plants which are 
to be found both in the desert and in the region of evergreen oaks. 
A first and most general observation of these vegetational stages will 
discover the distinctive regions of desert, of park-like semi-desert and 
of forest. The first is like the desert of the extensive bajada slopes 
which surround the entire mountain; the second is similar to plant 
