Report on the lands of the arid region of the United States, with a more detailed account of the lands of Utah

by John Wesley Powell; Willis Drummond; Clarence E. Dutton; Grove Karl Gilbert; A. H. Thompson

CHAPTER I.
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 precipitation, 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 eastward 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 mountains, definite boundary lines are unimportant in the consideration of agricultural resources and the questions relating thereto. In like manner on the east the rain gauge records, though more full, do not give all the facts necessary to a thorough discussion of the subject; yet the records are such as to indicate approximately the boundary between the Arid Region, where irrigation is necessary to agriculture, and the Humid Region, where the lands receive enough moisture from the clouds for the maturing of crops. Experience teaches that it is not wise to depend upon rainfall where the amount is less than 20 inches annually, if this amount is somewhat evenly distributed throughout the year; but if the rainfall is unevenly distributed, so that “rainy seasons” are produced, the question whether agriculture is possible without irrigation depends upon the time of the “rainy season” and the amount of its rainfall. Any unequal distribution of rain through the year, though the inequality be so slight as not to produce “rainy seasons”, affects agriculture either favorably or unfavorably. If the spring and summer precipitation exceeds that of the fall and winter, a smaller amount of annual rain may be sufficient; but if the rainfall during the season of growing crops is less than the average of the same length of time during the remainder of the year, a greater amount of annual precipitation is necessary. In some localities in the western portion of the United States this unequal distribution of rainfall through the seasons affects agriculture favorably, and this is true immediately west of the northern portion of the line of 20 inches of rainfall, which extends along the plains from our northern to our southern boundary.

The isohyetal or mean annual rainfall line of 20 inches, as indicated on the rain chart accompanying this report, begins on the southern boundary of the United States, about 60 miles west of Brownsville, on the Rio Grande del Norte, and intersects the northern boundary about 50 miles east of Pembina. Between these two points the line is very irregular, but in middle latitudes makes a general curve to the westward. On the southern portion of the line the rainfall is somewhat evenly distributed through the seasons, but along the northern portion the rainfall of spring and summer is greater than that of fall and winter, and hence the boundary of what has been called the Arid Region runs farther to the west. Again, there is another modifying condition, namely, that of temperature. Where the temperature is greater, more rainfall is needed; where the temperature is less, agriculture is successful with a smaller amount of precipitation. But geographically this temperature is dependent upon two conditions—altitude and latitude. Along the northern portion of the line latitude is an important factor, and the line of possible agriculture without irrigation is carried still farther westward. This conclusion, based upon the consideration of rainfall and latitude, accords with the experience of the farmers of the region, for it is a well known fact that agriculture without irrigation is successfully carried on in the valley of the Red River of the North, and also in the southeastern portion of Dakota Territory. A much more extended series of rain-gauge records than we now have is necessary before this line constituting the eastern boundary of the Arid Region can be well defined. It is doubtless more or less meandering in its course throughout its whole extent from south to north, being affected by local conditions of rainfall, as well as by the general conditions above mentioned; but in a general way it may be represented by the one hundredth meridian, in some places passing to the east, in others to the west, but in the main to the east.

The limit of successful agriculture without irrigation has been set at 20 inches, that the extent of the Arid Region should by no means be exaggerated; but at 20 inches agriculture will not be uniformly successful from season to season. Many droughts will occur; many seasons in a long series will be fruitless; and it may be doubted whether, on the whole, agriculture will prove remunerative. On this point it is impossible to speak with certainty. A larger experience than the history of agriculture in the western portion of the United States affords is necessary to a final determination of the question.

In fact, a broad belt separates the Arid Region of the west from the Humid Region of the east. Extending from the one hundredth meridian eastward to about the isohyetal line of 28 inches, the district of country thus embraced will be subject more or less to disastrous droughts, the frequency of which will diminish from west to east. For convenience let this be called the Sub-humid Region. Its western boundary is the line already defined as running irregularly along the one hundredth meridian. Its eastern boundary passes west of the isohyetal line of 28 inches of rainfall in Minnesota, running approximately parallel to the western boundary line above described. Nearly one-tenth of the whole area of the United States, exclusive of Alaska, is embraced in this Sub-humid Region. In the western portion disastrous droughts will be frequent; in the eastern portion infrequent. In the western portion agriculturists will early resort to irrigation to secure immunity from such disasters, and this event will be hastened because irrigation when properly conducted is a perennial source of fertilization, and is even remunerative for this purpose alone; and for the same reason the inhabitants of the eastern part will gradually develop irrigating methods. It may be confidently expected that at a time not far distant irrigation will be practiced to a greater or less extent throughout this Sub-humid Region. Its settlement presents problems differing materially from those pertaining to the region to the westward. Irrigation is not immediately necessary, and hence agriculture does not immediately depend upon capital. The region may be settled and its agricultural capacities more or less developed, and the question of the construction of irrigating canals may be a matter of time and convenience. For many reasons, much of the sub-humid belt is attractive to settlers: it is almost destitute of forests, and for this reason is more readily subdued, as the land is ready for the plow. But because of the lack of forests the country is more dependent upon railroads for the transportation of building and fencing materials and for fuel. To a large extent it is a region where timber may be successfully cultivated. As the rainfall is on a general average nearly sufficient for continuous successful agriculture, the amount of water to be supplied by irrigating canals will be comparatively small, so that its streams can serve proportionally larger areas than the streams of the Arid Region. In its first settlement the people will be favored by having lands easily subdued, but they will have to contend against a lack of timber. Eventually this will be a region of great agricultural wealth, as in general the soils are good. From our northern to our southern boundary no swamp lands are found, except to some slight extent in the northeastern portion, and it has no excessively hilly or mountainous districts. It is a beautiful prairie country throughout, lacking somewhat in rainfall; but this want can be easily supplied by utilizing the living streams; and, further, these streams will afford fertilizing materials of great value.

The Humid Region of the lower Columbia and the Sub-humid Region of the Great Plains have been thus briefly indicated in order that the great Arid Region, which is the subject of this paper, may be more clearly defined.

THE ARID REGION.

The Arid Region is the great Rocky Mountain Region of the United States, and it embraces something more than four-tenths of the whole country, excluding Alaska. In all this region the mean annual rainfall is insufficient for agriculture, but in certain seasons some localities, now here, now there, receive more than their average supply. Under such conditions crops will mature without irrigation. As such seasons are more or less infrequent even in the more favored localities, and as the agriculturist cannot determine in advance when such seasons may occur, the opportunities afforded by excessive rainfall cannot be improved.

In central and northern California an unequal distribution of rainfall through the seasons affects agricultural interests favorably. A “rainy season” is here found, and the chief precipitation occurs in the months of December-April. The climate, tempered by mild winds from the broad expanse of Pacific waters, is genial, and certain crops are raised by sowing the seeds immediately before or during the “rainy season”, and the watering which they receive causes the grains to mature so that fairly remunerative crops are produced. But here again the lands are subject to the droughts of abnormal seasons. As many of these lands can be irrigated, the farmers of the country are resorting more and more to the streams, and soon all the living waters of this region will be brought into requisition.

In the tables of a subsequent chapter this will be called the San Francisco Region.