The Grazing-Irrigated Region

Wynne Thorne.

Mountains dominate the grazing-irrigated region of the West. The main spine of the Rockies divides the region somewhat east of center. The Sierra Nevada and the Coastal ranges on the west intercept moisture moving in from the Pacific; less rain falls east of them.

Precipitation is heavier near the western slope of the Rockies and reaches a maximum of 50 inches or more at the highest elevations. Rainfall again tapers off east of the Rockies, but not so much as in Nevada and western Utah.

Great variations sometimes occur within short distances. A small valley near the mountains may be covered with grass and trees, while less than 10 miles away the parched earth and scanty desert shrub vegetation give evidence of a drastically reduced rainfall. Many valleys in the mountains have occasional frosts in every month.

The mountains are less pronounced in Arizona and New Mexico. Desert conditions prevail generally. Rainfall is inadequate for crop production. Summer temperatures are high. Winters are mild. Some farming areas average 250 frost-free days a year.

A Great Plains type of climate prevails east of the Rocky Mountains. Temperatures often change quickly. Fluctuations in precipitation and temperature are greater than in the intermountain area.

The grazing-irrigated region is a land of extremes. People who are accustomed to the natural richness of the prairies and the humid forest lands may be appalled by the apparent aridity of much of this intermountain region when they see it the first time. They may agree with the report of Brigham Young's exploring parties that the only use of the land is to hold the rest of the earth together.

But close study of the agriculture of the region shows that there are essentially no wastelands. There are only different intensities of use. Productive irrigated pastures may graze a cow or more per acre but in a desert shrub area 75 acres or more may be needed for one cow.

Irrigation is the key to an intensive agriculture in this area. Surplus moisture from the high elevations (principally above 7 thousand feet) is used on lands below. Ground waters are also pumped to supplement the water in streams and reservoirs.

The supply of irrigation water is adequate for only a small part of the land. Lands are chosen for irrigation according to suitability of topography for intensive agriculture, quality of the soil, and nearness to a water supply. Because less than 5 percent of the region is irrigated, the pattern of irrigated land appears on a map as only thin belts or isolated spots in the broad terrain of rangeland.

The intimate association of irrigated lands and rangelands favors livestock farming. The animals graze the range in appropriate seasons, and supplemental feed for them is grown under irrigation. Poultry and dairy industries are confined to irrigated regions and usually are concentrated near cities.

Income from livestock, other than from poultry and dairying, is more than 600 million dollars a year. The agricultural income from dairy products exceeds 100 million dollars and income from poultry is about 60 million dollars a year. Cash crops, another major source of income, bring more than 525 million dollars a year. Fruits, berries, and vegetable crops are major enterprises in some localities. Field crops, including sugar beets, potatoes, dry beans, small grains, corn, and sorghums, are grown extensively. Cotton is important in parts of Arizona, New Mexico, and Texas.

Noted for fruit production are the Yakima and Wenatchee areas of central Washington, parts of the Boise Valley of Idaho, the Flathead Lake region of Montana, the Wasatch Front region of Utah, the Virgin River Valleys of Utah and Nevada, the western slope of Colorado, and some of the irrigated valleys in eastern California.

General farming and cash crops are important in the Columbia Basin of Washington; the Lower Snake River area of Oregon and Idaho; the Upper Snake River Valleys of Idaho; Salt Lake, Utah, and Sevier Valleys of Utah; Yellowstone Valley, Big Horn Valley, and North Platte River areas of Wyoming; the eastern slope of Colorado, including the headwaters of the South Platte River; and the San Luis Valley at the headwaters of the Rio Grande. The lands along the Rio Grande and Pecos Rivers in New Mexico and Texas are irrigated and used for general farming, including cotton in the lower elevations.

Nonirrigated crops are important in scattered areas. Dry beans are grown in summer-rainfall areas of central New Mexico, southwestern Colorado, and southeastern Utah. Dryland wheat is important near the Palouse area, in south-central and southeastern Idaho, and in northern Utah. Alfalfa, barley, and wheatgrasses are also important. Native vegetation and soil characteristics are closely associated with climate. Short grasses are the dominant native vegetation east of the Rocky Mountains. Trees, grass, and shrubs appear in the mountains according to moisture, temperature, and soil conditions. Desert shrubs and the bunch grasses are dominant west and south of the Rockies. Sagebrush, rabbitbrush, greasewood, creosote bush, shadscale, and other shrub and browse plants predominate according to environmental conditions. Native plants remain on more than 90 percent of the land, and their character and density are major factors in determining the numbers of livestock that can be grazed.

Almost every major great soil group in the United States exists in this region. Soils typical of humid areas and forests occur principally in the high mountain areas and are not farmed, except in northern Idaho and Washington. The principal cultivated soils are those representative of and zones.

Arid-region soils are generally low in organic matter and nitrogen; the amounts reflect somewhat the climate and native vegetation. Shrubs and bunch grasses are the principal vegetation in places where rainfall is less than 10 inches. The soils are light in color, alkaline in reaction, and often high in content of lime and mineral nutrients. Moisture is inadequate for farming except with irrigation. Such soils need organic matter for successful farming, and until it is supplied the soils run together and crust excessively.

As rainfall increases, native vegetation changes to sagebrush and larger shrubs and bunch grasses, then to short grasses. The content of organic matter in the soil increases accordingly and permits wider varieties of farming and farm crops. In most of the unforested parts, precipitation has been inadequate for leaching, and the soils therefore are generally alkaline in reaction and rich in mineral nutrients. Zones of lime accumulation are typical. They are near the surface in the deserts and progressively deeper in the higher rainfall belts.