REPORT ON THE LANDS OF THE ARID REGION OF TIE UNITED STATES, 
By J. W. POWELL. 
PHYSICAL CHARACTERISTICS OF THE ARID 
REGION. 
The eastern portion of the United States is supplied with abundant 
rainfall for agricultural purposes, receiving the necessary amount from the 
evaporation of the Atlantic Ocean and the Gulf of Mexico; but westward 
the amount of aqueous precipitation diminishes in a general way until at 
last a region is reached where the climate is so arid that agriculture is not 
successful without irrigation. This Arid Region begins about midway in 
the Great Plains and extends across the Rocky Mountains to the Pacific 
Ocean. But on the northwest coast there is a region of greater precipita- 
tion, embracing western Washington and Oregon and the northwest corner 
of California. The winds impinging on this region are freighted with 
moisture derived from the great Pacific currents ; and where this water- 
laden atmosphere strikes the western coast in full force, the precipitation is 
excessive, reaching a maximum north of the Columbia River of 80 inches 
annually. But the rainfall rapidly decreases from the Pacific Ocean east- 
ward to the summit of the Cascade Mountains. It will be convenient to 
designate this humid area as the Lower Columbia Region. Rain gauge 
records have not been made to such an extent as to enable us to define its 
eastern and southern boundaries, but as they are chiefly along high moun- 
tains, definite boundary lines are unimportant in the consideration of 
agricultural resources and the questions relating thereto. In like manner on 
the east the rain gange records, though more full, do not give all the facts 
necessary to a thorough discussion of the subject; yet the records are such 
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