| OCR Text |
Show inches annually as stream flow, while the remainder of the basin produces only about 1.3 inches of runoff. Erosion.-Large parts of the basin have been im- paired by water and wind erosion. Estimates based on inspection of public domain lands show that the degree of erosion is approximately as follows:2 Percent Land on which erosion is negligible or slight_______ 18 Land with moderate erosion, including sheet wash and some rilling------------------------------------------ 32 Land with severe to critical erosion which includes development of deep gully systems and exten- sive sheet wash------------------------------------------- 50 Watershed conditions in the States of the basin differ, but there are severe problems in all. Sur- veys of the Soil Conservation Service in the past have shown conditions in the basin States to be about as follows: In Arizona, erosion is taking place in nearly two- thirds of the State, the greater part on public lands. Gullying occurs on about 45 million acres and is severe on 32 million acres of these. Loss of more than three-fourths of the topsoil is the prevailing condition on some 3.5 million acres, and a loss of half the topsoil is prevalent on over 20 million acres in the State. Wind erosion is serious on about 6 million acres. Some national forests, many of the Indian and grazing district lands, and most State lands are in poor condition. Many of the agricultural lands have lost their fertility through loss of the topsoil, and erosion is a relatively com- mon result of the irrigation practices followed. In the Colorado River section of Colorado about 75 percent of the public lands and 50 percent of the private are eroding. Gullying and other erosion are especially severe in the San Juan drain- age. It is serious on some of the higher mesas and in the lower semiarid section of the western slope. Misuse of agricultural lands is responsible for much erosion. Much of the Colorado Basin in Nevada is rough, with many mesas of igneous rocks, on which a thin soil mantle has developed. The cover has been so depleted by misuse that erosion of some type is generally common. Gullying of deeper soils is common in the Virgin River drainage. A large part of the eroded land is in public ownership, al- though many privately owned agricultural lands also are badly eroded. Much of the New Mexico part of the Colorado Basin is in public ownership, and it is on these 2 U. S. Department of the Interior. public lands that the greatest amount of erosion takes place. It is widespread, and the material produced from this erosion is a cause of serious sedi- mentation. Gullying, much of it serious, occurs on perhaps 40 percent of the public lands. Great arroyos are cut deeply into the unconsolidated soils. Small drainage ways that a man once could step across have in 25 years or so become a quarter of a mile wide and 100 feet deep. Sheet erosion on some of the lands has been so great as to leave the surface roots of juniper and pinon pines uncovered over many acres. Most of the serious erosion in Utah occurs on public lands, both Federal and State. About half the area is affected. Gullying has been found prominent on some 11 million acres, of which 8 million acres are seriously gullied. This gully- ing has taken place in the mountain area and on the broad plateau basins. The loss of topsoil from many areas is responsible for the lack of cover. In the mountain areas, deep channeling has resulted from cloudbursts. Mud-rock flows, which in some places have cut channels over 50 feet deep, have caused much local damage. Outside of the more heavily forested sections, erosion is serious. In places it has reached a stage where land virtually has been ruined by removal of the surface soil and by deep gullying. Over many of the public lands erosion has been severe. Range Lands.-Grazing developed early in the West. It began on a large scale with the advent of the Spanish in the Southwest, and by 1870 cattle and sheep were grazed in numbers, mostly on public lands where there were no controls. First-comers were entitled to the grass and no one was respon- sible for the condition of the range. In most instances, the livestock followed the range from the lowland areas to mountain meadows as the season advanced. However, when the national forests were created from the public domain, rules regarding range use were established. Gradually these controls on the summer range-and to some extent on the spring and fall range-had a marked effect. They forced local stock on the public domain lands for longer periods, thus helping to overgraze the nonforest ranges. They caused the elimination of some stock because of range pressures and forced the development of hay lands and irrigated pastures as a means of supplying added feed for stock. With each grazer using the land to the utmost, both public and private ranges were seriously overgrazed and in drought years conditions were 367 |
