far separated in
latitude differ but little in average temperature, their summers
being cooler and their winters warmer than we should expect them
to be.

(3) The storms pass over the land with the general easterly movement
of the air. The largest number pass east across the northern portion
of the United States. The farther south we go the fewer are the
storms and the less the rainfall. Along the coast of Washington
the annual rainfall is nearly one hundred inches. At San Diego
it is only about ten inches.

(4) The position of the mountain ranges causes the influence of
the ocean on the air to be lost within a short distance toward
the interior of the continent, so that the extremes of temperature
rapidly become greater. The position of the mountains also affects
the rainfall of the interior. Since a large proportion of the moisture
is condensed upon their ocean slopes, the climate of each succeeding
range toward the interior becomes more dry and desert-like. While
in some of the lowlands thus cut off from the ocean the climate is
extremely arid, yet the country is relieved from utter barrenness
through the presence of mountain peaks and ranges, which often
condense considerable moisture.

[Illustration: FIG. 112.--SCENE IN FORESTS OF WASHINGTON

Showing spruce and cedar]

(5) The higher a region is above the sea, the colder the climate.
The summit of a high mountain and the valley at its base may be
in the same latitude, and yet one may possess an arctic climate
while the other has a sub-tropical one.

The heavy rainfall in western Washington, Oregon, and northern
California results in dense forests. To the south, the rainfall
upon the lowlands is not sufficient to produce forests, but as
it is greater upon the mountains, trees thrive upon their sides.
The elevation at which trees will grow becomes higher and higher
as we go into the more desert regions, until in northern Arizona
it is found to be above six thousand feet. The high plateaus are
generally treeless, but are covered with such shrubs as greasewood
and sage-brush.

We see now that our climate is the product of many factors. It
frequently varies greatly in places only a few miles distant from
each other. Consequently there may be a great variety of productions
and industries in one small area, while in other regions the climate
and productions are almost unchanged for hundreds of miles.

SOMETHING ABOUT IRRIGATION

Travellers from the Ea