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 Canon 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 canon and prevented the outwash of 

 erosion material. Similarly, in Soldier Canon 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 sunomit 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 to a loam 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 sufl&ciently deep for shrubs and trees to 



