a classification there is an unavoidable overlapping.  However, no one factor so fully represents varying degrees of aridity as the annual precipitation, and there is a great need for concise definitions of the terms used in describing the parts of the country that come under dry-farming discussions.  In this volume, the terms “arid,” “semiarid,” “sub-humid” and “humid” are used as above defined.

Precipitation over the dry-farm territory

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
South Dakota 76,850
Washington 66,880
total 653,095

Sub-Humid to Humid Group

Kansas 81,700
Minnesota 79,205
Oklahoma 38,830
Texas 262,290
total 462,025

GRAND TOTAL 1,861,652

The territory directly interested in the development of the methods of dry-farming forms 63 per cent of the whole of the continental United States, not including Alaska, and covers an area of 1,861,652 square miles, or 1,191,457,280 acres.  If any excuse were needed for the lively interest taken in the subject of dry-farming, it is amply furnished by these figures showing the vast extent of the country interested in the reclamation of land by the methods of dry-farming.  As will be shown below, nearly every other large country possesses similar immense areas under limited rainfall.

Of the one billion, one hundred and ninety-one million, four hundred and fifty-seven thousand, two hundred and eighty acres (1,191,457,280) representing the dry-farm territory of the United States, about 22 per cent, or a little more than one fifth, is sub-humid and receives between 20 and 30 inches of rainfall, annually; 61 per cent, or a little more than three fifths, is semiarid and receives between 10 and 20 inches, annually, and about 17 per cent, or a little less than one fifth, is arid and receives less than 10 inches of rainfall, annually.