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RANGE MANAGEMENT IN NEW MEXICO. 3 
Socorro ‘County and the Estancia Valley in Torrance County are 
typical examples. These plains are everywhere dissected by dry 
watercourses, or arroyos; which serve to collect the flood waters that 
are sometimes temporarily very abundant, and sheet erosion of unpro- 
tected soil surfaces is everywhere very rapid, largely because of the 
steep gradient of even that part of the surface, which, by comparison 
with the bolder relief features, seems to be level. Many of the striking 
topographic features, both of sculpture and deposition, are due to 
wind action. On the eastern side of the State the mountains and 
mesas gradually subside into the wide expanse of the Staked Plains, 
while to the west Arizona is but a repetition of the alternation of 
plains and mountains so characteristic of New Mexico but at a slightly 
lower general level. 
The river valleys are narrow and not infrequently constricted to the 
river channels alone or ‘‘boxed in”’ where they cut through moun- 
tains or mesas. The two largest rivers, the Rio Grande and Rio 
Pecos, run entirely or almost across the State from north to south. 
The San Juan and the Gila flow out of the State westwardly in San 
Juan and Grant Counties, respectively, while the northeastern part 
of the State contains some of the tributaries of the Arkansas River 
and the headwaters of the Canadian, all of which flow eastwardly. 
The most conspicuous feature of all these streams is the small number 
of permanent tributaries possessed by each when the size of its drain- 
age area is considered. The valley bottoms throughout the State, 
wherever there is a permanent flow of water, are always turned into 
cultivated fields, and many acres of such lands produce alfalfa. 
(PL IL, fig. 2.) 
CLIMATE. 
Precipitation.—Precipitation is everywhere relatively smal! in 
amount in New Mexico. On the plains of the southern part of the 
- State and in all of the river valleys outside of the mountains it is 
always scanty. In the mountains at altitudes of 5,500 feet or more 
it is more abundant, but even in the more moist regions the amount 
of water that falls during the year is rarely equal to that which is com- 
mon in the humid regions farther east. | 
To say that there is a summer rainy season does not mean what the 
Same expression tells in regard to a tropical country. It merely says 
that most of the rain of the year comes during July, August, and Sep- 
tember, and that this is the growing season on the plains and almost 
everywhere in the mountains. In some of the higher mountains, 
where there is considerable snow during the winter, the ground is left 
_wet enough by the melting of these snows to cause a certain spring 
_ and early-summer growth; and some of the perennials of even the 
drier plains put out their bloss-ms and grow some new leaves in May 
