GEOGRAPHY AND TOPOGRAPHY OF SANTA CATALINA MOUNTAINS. 7 



feet, 2,875 m.). To the northeast of the San Pedro River rises the 

 GaUuro range of mountains, the main ridge of which is approximately 

 35 miles (57 km.) distant from the Santa Catalinas. The next moun- 

 tains encountered in passing northeastward are the Pinaleno or Graham 

 range, about 60 miles distant from the Santa Catahnas, and exceeding 

 them in altitude by about 1,400 feet (427 m.). Beyond the upper 

 course of the Gila River lie the Gila Mountains, and still further to the 

 northeast the White Mountains, which reach an elevation of 11,280 

 feet (3,440 m.) in Escudilla Peak. The White Mountains present one 

 of the largest elevated land masses of the State, connecting to the 

 northeast, through the Mogollon Mesa, with the elevated region which 

 surrounds the San Francisco Peaks and supporting a heavy body of 

 forest which extends from the New Mexican boundary nearly to the 

 Grand Canon. East of the White Mountains the elevated country ex- 

 tends for about 75 miles (121 km.) into New Mexico, breaking up into 

 several diverging ranges which form a part of the Continental Divide, 

 draining westward into the Gila and eastward into the Rio Grande. 



The Santa Catahna Mountains are thus seen to stand at the south- 

 western terminus of a series of isolated elevations which stretch away 

 from the southern edge of the Colorado Plateau. The valley of the 

 Rio Grande and its tributaries, several undrained basins, and the 

 valley of the Little Colorado combine to separate the entire chain of 

 elevations — San Francisco Mountains, Mogollon Mesa, White Moun- 

 tains, and the mountains of western New Mexico — from the Sangre 

 de Cristo, San Juan, and Jemez mountains of northern New Mexico, 

 which are virtually a part of the Rocky Mountain system. A consider- 

 able degree of isolation from the north is thus given to the entire series 

 of mountains in southeastern Arizona. 



To the south and southeast of the Santa Catalinas an irregular but 

 close-set series of mountains gives them a connection with the Mexican 

 Cordillera which is much closer than their connection with the Rocky 

 Mountains. To the west the nearest forest-clad elevations are the San 

 Jacinto and San Bernardino Mountains of southern California, which 

 are about 300 miles (480 km.) distant. 



The relative isolation of the Santa Catalina Mountains and the 

 directions in which they possess easy stages of connection with other 

 elevated regions are of first importance in relation to the genesis and 

 history of their flora, a subject which will be only briefly touched upon 

 in this paper (see p. 36). 



The southern face of the Santa Catalinas, to which the present in- 

 vestigation has been confined, is built solely of gneiss of varying degrees 

 of hardness. The main ridge and the northern and eastern lateral 

 ridges are worn into a relatively rounded topography, while the south- 

 western corner of the range possesses rock of greater durabihty and is 

 correspondingly more rugged in topography. 



