Nearly one half of the United States receives 20 inches or less
rainfall annually; and that when the strip receiving between 20 and
30 inches is added, the whole area directly subject to reclamation
by irrigation or dry-farming is considerably more than one half (63
per cent) of the whole area of the United States.

Eighteen states are included in this area of low rainfall. The areas
of these, as given by the Census of 1900, grouped according to the
annual precipitation received, are shown below:--


Arid to Semi-arid Group
Total Area Land Surface (Sq. Miles)

Arizona 112,920
California 156,172
Colorado 103,645
Idaho 84,290
Nevada 109,740
Utah 82,190
Wyoming 97,545
TOTAL 746,532

Semiarid to Sub-Humid Group

Montana 145,310
Nebraska 76,840
New Mexico 112,460
North Dakota 70,195
Oregon 94,560