GEOGRAPHY AND TOPOGRAPHY OF SANTA CATALINA MOUNTAINS. 7 
feet, 2,875 m.). To the northeast of the San Pedro River rises the 
Galiuro 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 Catalinas, and exceeding 
them in altitude by about 1,400 feet (427m.). 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 Cafion. 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 Catalina 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 durability and is 
correspondingly more rugged in topography. 
