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RANGE MANAGEMENT IN NEW MEXICO. 95 
Whatever may be said of the undesirability of weeds on a range, 
there is one thing to be said in their favor. Any vegetable covering 
in an arid region is better than none, since such a covering prevents 
to some degree the removal of the soil, and any plant association 
occupying an area is to be looked upon as merely one stage in the 
production of that ultimate assemblage of plants which is best 
adapted to that place and its conditions. 
EROSION. 
To the observer from a humid climate, perhaps no one charac- 
teristic of the arid regions of the Southwest is so startling as the evi- 
dence on all sides of the forceful action of water as an erosive agent. 
And this in a land where water is the one thing that is everywhere 
lacking. 
But the reason is patent after a summer in the region, and the 
conditions are common to all arid countries of high relief. The ero- 
sive effects that one sees so plainly are the resultant of several factors. 
During the warm weather, the only season of the year in which large 
volumes of moist air are brought into the region, the air next the 
ground is always warm and therefore relatively dry. Hence, rain 
occurs only when masses of humid air are forced into the cold upper 
strata. Such conditions arise only locally and produce showers of 
restricted size, but such showers are mostly torrential in character, 
a large amount of water falling on a restricted area in a very short 
time. 
Let such a downpour occur on what seems to be a flat plain, and 
in a few minutes the lower levels are flooded and the-roadbed of any 
obstructing railroad is apt to suffer severely. Thus, we are forever 
hearing of railroad washouts in a region that is called a desert and 
is wanting governmental irrigation systems established. (Pl. VIII, 
fig. 2.) 
‘The land is but sparsely covered with any kind of vegetation and 
there is little to obstruct the run-off. The gradient is high at almost 
any place. Add to this the fact that the soil has been loosened by 
daily expansion and nightly contraction, due to large diurnal varia- 
tions of temperature, and the conditions for maximum efficiency of 
the erosive agent are supplied; and the consequences are not only 
not singular but were to be expected instead of wondered at. 
The factor which more than anything else tends to prevent the 
same kind of results in a humid region on an even larger scale is the 
protective cover of vegetation everywhere abundant, and no one fac- 
tor is so efficacious in producing rapid erosion on the arid grazing 
~ lands as the more or less complete removal of their already scanty 
cover of plants by overstocking. 
