8 VEGETATION OF A DESERT MOUNTAIN RANGE. 



The highest elevations lie between Mount Lemmon (9,150 feet, 

 2,790 m.) and Green Mountain (7,900 feet, 2,410 m.), which are only 

 7 miles (11 km.) apart. Samaniego Ridge and Oracle Ridge extend 

 northward from the vicinity of Mount Lemmon, falling rapidly in 

 elevation and terminating in the high plain which lies in the direction 

 of the Tortilla Mountains. A very rugged ridge extends southwest- 

 ward from Mount Lemmon and terminates in Pusch Ridge. To the 

 south of the main ridge an extensive elongated drainage basin has been 

 developed which lies parallel to the south face of the range and finds 

 its outlet through Sabino Canon. Several important streams drain the 

 south slopes of the main ridge and are tributary to Sabino Canon. To 

 the east of Sabino two important drainages — Bear Canon and Soldier 

 Caiion — drain the eastern end of the main ridge in the vicinity of Green 

 Mountain, and west of Sabino are Pedregosa, Ventana, Pima, and other 

 canons which rise in the rugged southwestern portion of the mountain. 

 All of these streams flow into the Rillito, a tributary of the Santa Cruz 

 which also drains a portion of El Rincon range. The north face of the 

 main ridge between Oracle and Samaniego ridges is drained by the 

 Canada del Oro, which flows at first north, then west, and finally south- 

 west, emptying into the Santa Cruz. On the northeast slopes of the 

 range the topography is relatively simple, the high elevations falling 

 away rapidly in the direction of the San Pedro River. A large number 

 of minor streams drain this region and give to the San Pedro perhaps 

 less than one-fourth of the total run-off of the mountains. 



The main drainageway of Sabino Canon is the only one in the Santa 

 Catalinas which possesses a constant flow of water, which is due both 

 to the great extent of its cachment basin and to the fact that it has 

 its source on the north slopes of Mount Lemmon in the heaviest body 

 of timber on the mountain. In the Caiiada del Oro, in Bear and Soldier 

 Canons, as well as in a few of the larger canons of the north slopes, 

 water may be found at all times of the year in certain locaUties where 

 the local configuration of the valley or the occurrence of resistant dikes 

 of rock forces the underflow to the surface. During the rainy seasons 

 water may, of course, be found in any of the large drainageways. The 

 heavy local showers of summer often convert even the smallest stream- 

 ways into rushing torrents for a few hours. 



The small size of the Santa Catalinas together with their elevation 

 gives a steep gradient to all of the major streams. The main stream 

 of Sabino Caiion falls from 7,700 feet at Webber's Cabin to 3,700 feet 

 at the west end of Sabino Basin, a distance of 6 miles, or a gradient 

 of fall of 667 feet per mile. From the west end of the Basin to its 

 emergence onto the desert this stream falls only 1,000 feet in a distance 

 of 5 miles. The Canada del Oro falls at a rate of 494 feet to the mile 

 from its source, just west of Mount Lemmon, to the confluence of its 

 main tributary from the west slopes of the Oracle Ridge, and at the 



