GEOGRAPHY AND TOPOGRAPHY OF SANTA CATALINA MOUNTAINS. 9 
rate of 200 feet to the mile from there to its emergence from the moun- 
tain at 3,400 feet. The result of the passage of intermittent and tor- 
rential streams through such steep drainageways has been the wearing 
down of the stream beds to solid rock throughout almost the entire 
drainage system of the mountain. There are no parks nor mountain 
meadows, such as are present in some of the largest southwestern 
mountains. The flood-plains and alluvial bottoms are all small and 
scattered. The spots in which meandering streams may be found are 
very few indeed. In Bear Cafion a flood-plain nearly half a mile in 
length has been formed as a result of a large body of highly resistant 
rock, which has narrowed the cafion and prevented the outwash of 
erosion material. Similarly, in Soldier Cafion there is a small flood- 
plain below which the stream falls 300 feet in a very short distance 
through a narrow gorge. Although Sabino Basin is a locality in which 
several converging streams undergo a sudden reduction in their gradi- 
ent of fall, there has not been any considerable deposition at that place. 
On the contrary the region is one in which the streamways are bordered 
and bedded by large boulders in a matrix of coarse sand and are sub- 
jected to active scouring by the torrential floods of summer. 
Whatever may have been the original form of the Santa Catalinas 
they have been so far worked upon by erosion and weathering that 
they now possess almost no relatively level areas or regions of inde- 
terminate drainage. All of the higher portions of the main ridge and 
of the lateral ridges as well are extremely narrow. The only localities 
in which the topography broadens and is relatively level are at points 
where several drainages have their origin, or places just above precipi- 
tous cliffs. On the summit of Mount Lemmon there is a nearly level 
area of at least 100 acres (see plate 36 a and B), from which a flat-topped 
ridge extends eastward for half a mile, terminating in an abrupt drop, 
in the course of which two narrow ridges have their origin. This re- 
stricted area of nearly level land is a last relic of a portion of the original 
structural form of the mountain, and it will not be many centuries 
until it is reduced to the narrow form of the lower ridges. 
In the eastern and central portion of the Santa Catalinas the gneiss 
weathers readily and gives rise toaloam soil. The precipitate topog- 
raphy gives little opportunity for the accumulation of this soil, and 
it is thin in almost all localities. Throughout the lower portions of the 
range, below the pine forest, the soil has the appearance of being ex- 
tremely coarse by reason of the surface coating of angular fragments 
from 1 to 5 mm. in diameter. Surface drainage is able to move this 
material but slowly by reason of its size and angularity. Just beneath 
it may be found a fine soil, still mingled with coarse particles but held 
in place by the mulch of stones, which is analogous to ‘desert pave- 
ment.” The outcropping rock and larger boulders serve to retard 
erosion and to preserve a soil sufficiently deep for shrubs and trees to 
