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Show posited in lower- lying areas whenever the velocity of the water is decreased by a lessening of the stream gradient. In the Colorado River Basin, material that has been removed from other areas seldom benefits the land on which it is deposited, and usually does great damage. If erosion in the uplands has been going on very long, the sand, gravel, and inferior subsoil that is washed downstream covers the good bottom lands with a layer of inert materials. Reservoirs become choked with this sand and gravel, and with a fine slimy mud that kills fish and spoils recreation. Often the deposited materials interfere so seriously with water storage as to threaten the principal purpose for which the reservoirs were constructed. In extreme cases, such as the removal of all watershed vegetation by fire, reservoirs have been almost completely filled with soil during a single month of heavy rain. In the Southwest high rates of silting are largely the result of overgrazing, which induces extraordinary sheet and gully erosion. At the Elephant Butte and Zuni Reservoirs in New Mexico and Coolidge and Roosevelt Reservoirs in Arizona, the watersheds are subject to both sheet and wind erosion and to arroyo and gully development and the badlands type of dissection. In the watershed areas of the Zuni and Roosevelt Reservoirs, sheep grazing under arid conditions which has reduced the vegetal covering is responsible for much of the accelerated erosion. 52 When the retarding influences of vegetation and soil porosity are lost, floods increase in violence. There have always been floods, even under strictly natural conditions, but the nature and the enormous extent of recent deposits along thousands of streams are proof to geologists and soil surveyors that the floods of today have become increasingly violent and dangerous following the destruction of vegetation. 53 Some stockmen, and a few others, while admitting that these profound land changes have indeed commenced since the advent of heavy grazing, maintain that there is no true connection between the two, and that the real cause of the range deterioration is to be found in a recent change of 52 Soil Conservation Service, 1935, p. 16. 53 Lord, 1938, p. 13; Thornthwaite et al, 1942, p. 91. climate. This claim is not supported by recent careful investigations. 54 Examination of evidence in tree- rings, lake levels, cutting and filling of valleys, and in the development of pueblo peoples fails to reveal proof of any climatic change in the Southwest in the last 2,000 years. Climatic fluctuations of the magnitude experienced today have occurred, and intense storms and groups of intense storms have had their effect on the landscape, but if there has been any progressive change toward either a more humid or a more arid climate that trend is so slight as to be completely overshadowed by the shorter period fluctuations. 55 Hunting, fishing, and trapping.- The pioneer days, marked by the careless, mass slaughter of wildlife- when millions of waterfowl glutted the meat markets, when antelope were hauled to town by the wagonload, and buffalo were shot by the thousands for their tongues alone, or for fun- are gone. Before the killing was stopped by belated conservation laws, some of the most incredibly abundant wildlife species had been nearly exterminated and several had vanished forever. Nevertheless, as far as hunting and fishing are concerned, the picture today is no longer black. Conservation organizations have sprung up in great numbers, many of them organized by hunters and fishermen. Conservation of natural resources is taught in the schools, and many universities now offer comprehensive training in the field of wildlife management, which has become a recognized profession. State and Federal protective legislation has become more and more responsive to the demands of national conservation groups, and, in recent years, has begun to take into account the investigations and recommendations of trained biologists. Some threatened species already have been partially restored, or at least rescued from extinction. Much progress in conservation education remains to be made, particularly in bringing about public and legislative recognition of the great value of many so- called " predators," the importance of which has been conclusively demonstrated by tlr* comprehensive investigations of innumerable fiela 54 Stewart, Cottam, and Hutchings, 1940, pp. 289- 292. 55 Thornthwaite et al, 1942, p. 125; cf. also pp. 43- 46, 123- 216. 65 |