2 BULLETIN 211, U. S. DEPARTMENT OF AGRICULTURE. 
here mainly concerned with the details of the purely physical basis 
of the industry, the factors of control and relation to other industries 
are so closely connected with any proper kind of management that 
they must be considered somewhat at length; and a study of range 
conditions is but preliminary to an understanding of methods of man- 
agement and the requirements-necessary for the further improvement | 
of the industry. 
» 
THE TOPOGRAPHY OF NEW MEXICO. 
New Mexico is almost square in outline, being about 350 miles long 
from north to south, nearly as wide at the southern end, and some- 
what narrower ‘lene the northern boundary. Only the southern 
boundary is a broken line. The State consists essentially of a high, 
arched plateau, the axis of the arch being near the middle and running 
north and south, the northern end being higher than the southern. 
This plateau is Syenie7 7,000 feet above sea level at its highest point on 
the northern boundary line and drops to about 3,500 feet at its south-_ 
ern end. 
Apparently resting upon this plateau, which is but a part of the 
great Rocky Mountain uplift, are numerous mountain ranges that 
seem to rise out of the sweeping plains as islands from the sea. These 
mountains are of two fairly well-defined types—narrow, rocky ridges, 
with but a scanty covering of low bushes and scattering trees, and 
ereat mountain masses, consisting of numerous associated ridges more 
or less densely covered with forests and woodland. Nearly all the 
main ranges have a northerly and southerly trend. Some of the 
mountains are composed of granites, rhyolites, gneisses, and other 
igneous and metamorphic rocks, while many of them are great mono- 
clinal piles of tilted, stratified rocks with sharp escarpment faces upon 
one side. In actual altitude they range from less than 5,000 feet to | 
more than 14,000 feet, there being numerous peaks and ranges over _ 
10,000 feet high. 
Large lava flows have occurred in several places, resulting in sheets 
of black, vesicular basalt, covering extensive areas. Associated with 
these flows are several large, extinct volcanoes and numerous small 
cones. The lava sheets have done much to modify the relief features, 
since the lava (or mal pais, as it is locally known) is harder than the 
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7 
underlying rocks and protects them from erosion. This has resulted — 
in a number of high mesas and buttes that almost take on the dimen- — 
sions of mountains. (PI. I, fig. 1.) 
The wide stretches of seemingly level plains that lie between the 
mountain ranges are nowhere really level. Many of them are typical 
bolsons, or basins, into which drains all the water that falls in the — 
region. ‘These bolsons are independent of each other and may occur ~ 
at any altitude (Pl. I, fig. 2). The San Augustine Plains in central | 
