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ENGINEERING WONDERS OF THE WORLD.
MAP SHOWING ARID, SEMI-ARID, AND HUMID
REGIONS OP THE UNITED STATES.
THE ARID REGIONS OF THE
UNITED STATES.
Roughly described, the arid regions of the
United States may be said to lie between the
western boundary of the Mississippi valley
and the Pacific coast. It comprises areas
differing widely in physical and climatic con-
ditions. West of the Missouri River is a vast
region called the Great Plains, extending to
the foothills of the Rocky Mountains, and
from the Panhandle of Texas northward into
Canada. Its boundary, as fixed by the ability
to produce crops without irrigation, is not
MAP OF WESTERN UNITED STATES, SHOWING NATIONAL FORESTS AND IRRIGATION PBOJECTS.