INTRODUCTION. 
The region which is called the Southwest in the title 
of this book is a natural geographical division lying 
south of the higher and more definite ranges of the 
Rocky Mountains. It is drained by the upper portion 
of the Rio Grande River and its tributary the Pecos, and 
by the Colorado River and its three main eastern 
branches, the San Juan, the Little Colorado, and the 
Gila. There are considerable ranges of mountains 
between the Rio Grande and the Pecos, and mountain 
masses north of the San Juan and at the head of the 
Gila. Mountain peaks somewhat isolated, such as the 
San Francisco Peaks (12,794) and San Mateo (11,389), 
_rise here and there. The Continental Divide, however, 
is for the most part unmarked by any definite elevation. 
The northern portion of the region is a high plateau 
with an average elevation of about 6,000 feet. This 
plateau is so sculptured that generally speaking the 
walls of both the elevations and the depressions are 
vertical. Instead of rounded hills and V-shaped valleys, 
we have for the most part flat-topped mesas and sheer- 
walled canyons. South and west of the watershed 
between the Little Colorado and the Salt, the country 
decreases in elevation very abruptly and then slopes 
to the low lying desert at the mouth of the Gila. 
Over much of the region evidences of considerable 
voleanic activity are found, consisting of extensive lava 
fields, dikes of projecting lava which can be followed for 
many miles, numerous extinct craters, and hot springs 
still active. 
The rainfall varies greatly according to the elevation, 
but is greater than is generally supposed. At Flag- 
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