in many directions by mountain ranges that are offshoots from the
backbone of the Rockies. South of the Great Basin are the high
plateaus, into which many great chasms are cut, the best known and
largest of which is the great Canon of the Colorado. North and east
of the Great Basin is the Columbia River Basin characterized by
basaltic rolling plains and broken mountain country. To the west,
the floor of the Great Basin is lifted up into the region of eternal
snow by the Sierra Nevada Mountains, which north of Nevada are known
as the Cascades. On the west, the Sierra Nevadas slope gently,
through intervening valleys and minor mountain ranges, into the
Pacific Ocean. It would be difficult to imagine a more diversified
topography than is possessed by the dry-farm territory of the United
States.

Uniform climatic conditions are not to be expected over such a
broken country. The chief determining factors of climate--latitude,
relative distribution of land and water, elevation, prevailing
winds--swing between such large extremes that of necessity the
climatic conditions of different sections are widely divergent.
Dry-farming is so intimately related to climate that the typical
climatic variations must be pointed out.

The total annual precipitation is directly influenced by the land
topography, especially by the great mountain ranges. On the east of
the Rocky Mountains is the sub-humid district, which receives from
20 to 30 inches of rainfall annually; over the Rockies themselves,
semiarid conditions prevail; in the Great Basin, hemmed in by the
Rockies on the east and the Sierra Nevadas on the west, more arid
conditions predominate; to the west, over the Sierras and down to
the seacoast, semiarid to sub-humid conditions are again found.