PLANT AND ANIMAL LIFE (continued)
Original conditions.The stories that early explorers brought back from the western wilderness of the incredible lushness and wealth of vegetation and wildlife read like fairy tales to us now, who will never see birds in flocks of millions that darken the earth for hours as they pass, or grass as tall as a man's shoulder, thronged with endless herds of buffalo, extending to the horizon. Civilization has left for present generations so little trace of the overwhelming primeval abundance of the "wild west" that the imagination, even when aided by the early records, now finds it almost impossible to reconstruct the original picture.
Because of the arid climate, the lowlands of the Colorado River Basin had a much less luxuriant vegetation than that of other regions in the West, such as the prairies and great plains on the east side of the Rockies. Nevertheless, by contrast with conditions in much of the basin today, the forage and the wildlife that it sustained were almost unbelievably abundant.
The vast sage plains of the Upper Green River Valley and the Red Desert in Wyoming were comparatively poorly stocked with game even in the early days  because of the scanty rainfall and the absence of water over large areas. Nevertheless, prior to 1850 there appears to have been considerable grass among the sage. Bands of antelope and buffalo roamed those regions where there was water  and sage hens came to the waterholes at evening by the thousands.  Elk in vast numbers wintered in the Red Desert. Now hundreds of thousands of domestic sheep use the region as winter pasture.  The buffalo have vanished, as has most of the grass, and the antelope and sage hens are but a small percent of their former numbers.
In the somewhat better-watered though still relatively barren sagebrush valleys of the Duchesne, White, and Yampa Rivers in northeastern Utah and adjacent Colorado there was good grass in 1844,  especially at the higher levels, and this condition lasted until about 1879. Buffalo were present, together with antelope  which sometimes were sold by the wagonload for meat. There were sage hens  and mountain plover in uncounted thousands, but, as elsewhere, these vanished at an early date. The upland plover, the existence of which now is threatened almost everywhere,  was "rather common" in 1877.  By 1892 the sharp-tailed grouse, once abundant, was rapidly disappearing as a result of overgrazing and burning. 
Even some parts of the Canyon Lands of Utah, now notable for the barrenness of their immense sandstone wastes, once were surprisingly fertile. Although cattle were abundant in the area by 1872, the Henry Mountains still stood in a valley of grass.  Antelope were seen frequently on the near by San Rafael Swell  as late as 1895 by the few persons who penetrated this wild region, although these animals disappeared not long thereafter. Antelope Valley, which is southwest of the San Rafael Swell, undoubtedly got its name from the former presence of this species.
The great valley of the Little Colorado River now is covered with a sparse, scrubby vegetation composed principally of semidesert shrubs with bare soil and desert pavement between the scattered plants. Although some areas may always have been barren, in 1857 grama grass on great areas of mesa land grew tall and rank between these shrubs.  Elk, deer, and beaver were common in the valley near Window and one the adjacent grassy plateaus and there were great herds of antelope.  Since 1852, herds of cattle and sheep have replaced the antelope bands, and the grass is abundant only at higher elevations in the basin where lack of water has prevented grazing by domestic stock. 
Even the vast, unpopulated southern desert lands which are commonly imagined as eternally unchanging would in many places hardly be recognizable to those who first discovered them. Many desert watercourses that present generations are accustomed to think of as dry washes, or as intermittent streams at most, once flowed the year round. The more luxuriant desert vegetation of those early days checked the run-off from the storms more efficiently than at present, thereby reducing the volume of flash floods and distributing the stream flow more uniformly throughout the year.
Those who are familiar with the bare, dry, sandy bed of the present intermittent Santa Cruz River at Tucson, in the heart of the Arizona Desert, will find it difficult to believe that prior to 1776 water there was so abundant that travelers sometimes had to wait for 6 weeks before it was possible to get horses across its swampy expanse. During the latter part of the eighteenth century the Spanish inhabitants of southern Arizona could ford the San Pedro and other rivers only at certain places.  Tucson was established at the site of the swamp on the Santa Cruz River because of the abundance of wood, water, and meadowland at that time. Where now there is only powder-dry desert, the grass once reached as high as the head of a man on horse back.  The river bottom then was densely forested with giant mesquites that formed a wide green belt extending down the valley for many miles. The region teemed with immense numbers of quail and doves. Peccaries and other wildlife of Mexican origin were abundant and beaver were plentiful.
After 1800, the valley was denuded of its mesquite forests, and the ironwood was stripped from the hills to feed the nearby lime kilns and provide fence posts. The beaver were trapped out and their dams destroyed. With the disappearance of the vegetation, the wildlife that depended on it also vanished. This history has been repeated in various degrees in the San Simon (once lush with grassy meadows), the San Pedro, and nearly every other mesquite valley of the Southwest.
Changes in the desert away from the river bottoms have been equally profound. Today we are accustomed to desert lands in which there is little or nothing between the widely spaced cacti and woody desert shrubs except rocks, gravel, or bare sand. However, before 1870, the spaces between the desert shrubs were quite generally filled with grama grasses,  and it was these highly nutritious grasses that maintained the herds of antelope that were common in those days.
After 1870, cattle increased greatly in the desert regions and the grama grasses thinned and disappeared. The trampling hoofs stripped the thin protecting layer of decaying plant materials from the surface of the soil, which then dried up, and gradually blew away, or was washed away by unchecked flood waters, leaving the bare gravel and sand that we know as "desert pavement." When the cattle removed most of the grass, the cacti and tough, unpalatable shrubs were able to multiply and predominate as they had not before.
Not only were the antelope starved out, but in some regions the character of the desert vegetation itself slowly changed. Seedlings of the giant saguaro of southern Arizona require moisture-holding duff and the protecting shade of dense, low-growing brush in order to establish themselves. Over great areas of the desert these necessary conditions were removed many years ago by the grazing of cattle and have never been restored.  The old saguaros that lend to the Arizona Desert much of its spectacular charm now stand on practically bare soil. They are commencing to die of old age, and with their disappearance will come a great change in the landscape and far-reaching reverberations among the desert birds and lesser wild creatures that depend upon the saguaros for their existence.
The new generation to replace the dying saguaro forests is sparse or lacking. Restoration of soil, decaying plant materials, and humus would require many years even if commenced at once. A saguaro seedling requires 10 to 15 years to grow to a noticeable size and 20 to 30 years to reach above the surrounding shrubbery. Thus the desert could hardly reverse its present trend within the next 50 years even if actually encouraged.
The fading picture of primeval beauty and abundance has not been confined to the valleys and deserts. The vegetation of the mountains originally was much more luxuriant and its resistance to grazing was greater, because the more abundant rainfall gave it greater vigor. However, the process of deterioration has been the same, although it has taken a little longer. In 1847, grass in some canyons of the Wasatch Mountains in Utah was from 6 to 12 feet high, and in some places the first explorers found themselves unable to penetrate the thickets which it formed. Today, the grass in these places often is less than 6 to 12 inches high, offering no obstacle to travel in any direction. Great numbers of unpalatable weeds and shrubs have replaced the original forage, of which many of the best kinds are on the verge of extinction. 
In 1844, Mountain Meadows, on the summit of the Colorado RiverGreat Basin divide in southwestern Utah, was a beautiful valley of green grass that extended for miles, bounded by piñon- and juniper-covered hills. By 1877, the grass had been mostly replaced by desert shrubs as a result of sheep grazing, and the appearance of the landscape was so greatly altered that landmarks of 20 years before could no longer be identified. Today the "meadow" is dry, and gray with sage. Great gullies have drained away the water, so that even if ungrazed, the grass could not come back. Junipers have been steadily invading the site of the vanished meadow from the surrounding hills since 1862.  These conditions are fairly typical of changes which have occurred throughout the mountains of the Colorado River Basin.
Animal life in the mountains has undergone a corresponding decrease, as a result of direct persecution, as well as from forage and habitat depletion. In primitive times, elk were abundant in nearly all the mountains and foothill valleys of Wyoming, Colorado, northeast Utah, central New Mexico, and northern Arizona as far west as the Hualpai Indian Reservation.
By 1910, they were nearly exterminated in the Colorado River Basin, but subsequently, determined efforts, particularly in Colorado, have restored them to part of their former range.
When the first white settlers came, bighorn in great numbers seem to have occupied nearly every canyon, cliff, and mountain range of the Colorado River Basin, but they began to decline about 1840.  By 1900, hunting, competition with domestic stock for the diminishing forage and water, changes in the type of forage plants, and diseases introduced by the domestic herds had reduced the bighorn to a dwindling fraction of their original numbers.
Beaver, which had molded American history for a century in the well-watered lands to the east and north, were remarkably abundant even in the Colorado River Basin in primitive times. In 1825, James O. Pattie caught 250 beaver in 2 weeks on the San Francisco River of Arizona and New Mexico.  The San Francisco is a tributary of the Gila River, which has but a meager stream flow today. Other trappers, including the famous Bill Williams, also found beaver abundant along the Gila and Salt Rivers.
Although beaver trappers had little success in the desolate gorges of the Colorado River in southern Utah, they found thousands of the animals in the more hospitable headwaters of the Green and Colorado Rivers. Individual trappers in the Rocky Mountains sometimes took as many as 500 beaver per year. However, the beaver's fate was like that of the buffalo, antelope, elk, bighorn, sage hen, turkey, grouse, and waterfowl. Though their original numbers had been immense, and though for untold thousands of years they had flourished in the presence of their natural enemies, the so-called predators, yet against the attacks of civilized man they held out less than 25 years before being brought to virtual or complete extinction. By 1840, the beaver market went into a decline from which it never recovered. Recent conservation measures have brought about good recovery in some areas, but the profound changes in the land brought about by human settlement and development make it impossible for the animals ever to regain their primitive numbers.
Almost as much a symbol of the wilderness of long ago as the buffalo is the wild turkey. In 1824, there were thousands of them in practically all the forested mountains and foothills of Arizona, New Mexico,  and southern Colorado (as well as in similar areas adjacent to the Colorado River Basin). In Arizona, they even came down from the mountains to the banks of the San Pedro River, which was thickly overgrown with giant mesquites at that time, and ventured into the desert far enough to feed on the fruits of the saguaro.  Wild turkeys now seldom wander from the ponderosa pine forests of the Transition Zone, and even in that zone they have been reduced to a fraction of their original numbers. In Texas, it has been shown that overgrazing eliminates many food plants required by wild turkeys. 
The chronicle of disappearance and deterioration throughout the Colorado River Basin since 1825 would be long if given in full, although the region has lost less of its primitive resources than have many other parts of the United States. To gloss over these great losses of the past would be futile, for the forces that brought about many of them continue almost unchecked even today. The only hope lies in recognizing them, in learning their causes, and in actively working to stop them now. An account of some of these causes follows, with an indication of remedial measures.
Changes caused by man.1. Farming. A fertile environment produces large numbers of plants and animals, but an infertile one can support few or none. This fundamental biological rule governs practically all living creatures, including man. It goes far toward explaining the widespread disappearance of wildlife following human occupation of the country.
The plains, foothills, and lower valleysnot the cold mountains or the rainless desertshave a virtual monopoly on the moisture, warmth, and deep, fertile soils that are necessary to produce abundant vegetation and other raw materials required by the higher forms of life. An abundant vegetation is required to feed the billions of insects, worms, and other invertebrate creatures that support the hordes of small birds and rodents. These, in turn, make possible the existence of such valuable fur bearers as the raccoon, marten, and the rare fisher, and the picturesque hawks and eagles which act as a "governor" to prevent the overproduction of the herbivorous animals.
An abundant vegetation is required also to sustain the deer, elk and antelope, beaver, wild turkey, grouse, and waterfowl that once swarmed over the plains and foothills in such numbers that they were thought to be inexhaustible. The same biological relationship between warmth, abundant food, and large numbers of animals enables the more fertile waters of the lowlands to support many more fish than can the waters of the mountains, and permits the individual fish to grow larger.
Although excessive fishing and the slaughter of game on a commercial scale were among the principal causes of wildlife depletion at the time that the country was settled, several more deep-seated causes soon commenced to operate and have continued to hasten disappearance of the original conditions long after the wholesale slaughter of the early days was halted by law. One of these causes of depletion has been the occupancy of most of the choice, fertile regions of the country by cities and farms.
Elk, deer, beaver, turkeys, and many other wild creatures, that in the West are considered today to be almost exclusively mountain dwellers, had their centers of abundance, particularly during the winter, in the lower hills and adjacent valleys. When these lowlands were cleared for farming or for the establishment of cities, the original plant-cover was destroyed and the animal life was forced to move, if it could. The elk and deer which previously had used the mountains primarily for summer range now were forced to live there the year round. Other less adaptable kinds of animals dwindled away or died out completely.
Retreat into the mountains, however, brought new problems of existence for those animals that were able to change their life habits in this manner. Fur-bearing animals found fewer rabbits, mice, and birds because the growing season for vegetation required by the latter was shorter at the higher altitudes. The deep, long-lasting snows often buried more than half of what browse there was beyond reach of elk and deer. Many mountain lakes used by waterfowl in summer froze solid in the winter months. The biological relations between numbers of animals and fertility of the environment immediately operated to maintain the migrants from the lowlands at a permanently low population. Competition between different kinds of animals for what little food there was became unnaturally severe during the winter months. Elk crowded into what was formerly a sheltered range of bighorn in the ponderosa pine belt, thereby forcing the bighorn to remain all winter on the higher, windswept areas above the timber line.  Today, the cold mountains and the rainless deserts are the principal remaining strongholds for many kinds of wildlife, not because they are the most suitable or productive areas, but because they are all that man has left in a relatively undisturbed condition.
However, wildlife has dwindled away in the desert, too, for settlements have been built around some of the best watering places. Water from many of the remaining scattered springs has been piped away to mines and ranches, and, as mentioned later, even the rivers have dried up. Where water still remains, it is often used so heavily by livestock that all vegetation in the immediate vicinity is destroyed, leaving no cover for game birds or other animals. Under such conditions the water is as unavailable as though it had been fenced or piped away.
2. Grazing. In the days of early settlement, grazing was carried on with the same reckless, competitive abandon as was the first cutting of timber and the commercial slaughter of wildlife for the meat market. No natural resource, however abundant in the beginning, has long withstood such wasteful use.
At the termination of the Civil War in 1865, the cattle business of the West entered a boom period comparable to the Gold Rush. In the scramble to get rich from the vast, new, unfenced lands, great syndicates were formed in the East and in England, and men and money poured in even from such far away places as Australia.
North and west from the Great Plains through the Uinta Basin in Utah and the Red Desert and the Upper Green River Valley in Wyoming, all the way to Canada, the tide rolled in. So abundant was the grass at first, even in that inhospitable climate, that no winter feeding was donean inconceivable practice today. With such overstocking the primitive grassland disappeared. The severe winter of 1886 brought about the end of boom times. Cattle perished by the thousands, and unlimited grazing without winter feeding in the Northwest States collapsed. By 1895, "not an acre of grazing land was left unoccupied, and ranges that for permanent and regular use would have been fully stocked with a cow to every 40 acres were loaded until they were carrying 1 to every 10 acres." 
In the Southwest the story was repeated a few years later. Grass grew more slowly than in northern regions because of the lighter rainfall. Although often luxuriant, the grass withstood the reckless grazing competition less easily because its moisture requirements were close to the danger line of water availability. Mountains and plains, stripped of their green covering, turned to dust. Freshets tore away the trampled sod of mountain meadows and cut deep gullies into the unprotected soil, thereby draining the meadows and turning them into deserts. In 1893, drought and ruination of the range brought the cattle boom of the Southwest crashing to a finish. 
The forage of the early days, like the wildlife, never has regained its primitive abundance. Perhaps it never will, even with the application of conservation measures learned in later years, for when the forage commenced to die from overuse, the soil began to die, too. Just as animals and plants are dependent upon one another for life, so are plants and the soil mutually dependent, both for their daily existence and their perpetual renewal.
Importance of topsoil.Topsoil, the life substance of grass, is a porous, chemically active medium, sometimes one-third to one-half air and from a tenth to one-fourth water.  In the surface layers of good topsoil, the air, the water, and the warmth of the sun combine to form a rich culture medium for a vast unseen world of struggling micro-organismsbillions of them to the square foot. Bacteria, protozoa, and microscopic fungi, during their own life processes, change the free nitrogen of the soil, and the nitrogen of decaying materials, into substances that plant roots can assimilate. By their endless rotting and disintegrating action on rocks and dead roots, on the bodies of other animals and last year's half-buried leaves, they keep the spaces between the soil particles open, whereby air, water, and warmth keep the fermentation process going on endlessly.
The microscopic soil-makers are aided by the millions of tiny worms and burrowing insect larvae that drag living and decayed vegetation, which they use for food, beneath the surface where the bacteria, too, can reach it. This yeasty brew of invisible, silently struggling creatures is a thin web of life draped over the mountains and valleys of the earth wherever there is topsoil. The chemicals which it distills are the life-juices that the roots of the plants must suck from the soil in order to live. Without topsoil, life for most plants is impossible.
However, topsoil seldom is more than 7 to 12 inches deep.  The chemical processes that form it, through the gradual decay of underlying rock, and the mixing of this rock with the products of organic decay derived from the surface of the soil above, are very leisurely. Some rich soils may accumulate at the rate of not more than 1 inch per 1,000 years.  Therefore, if a 7-inch layer of such a topsoil is removed, the full thickness cannot be replaced from the barren, chemically inert stratum of disintegrating rock beneath it in less than 7,000 years, even if all other conditions should be favorable for the required reaction.
Thus, when all of the topsoil is removed, the land dies, and with it die also the plants and the animals, whose lives are all so inextricably bound up together.
Difference between natural and man-caused erosion.Removal of the soil layers, by whatever means, is known as soil erosion. We are concerned with it in the Colorado River Basin because much of this soil erosion was caused by ruinous overgrazing in the early days of settlement. But first a frequent and dangerous misconception must be corrected regarding two very different kinds of erosion, and man's responsibility in relation to them.
Natural or geologic soil erosion is a slow process, except in a few special areas. It is so slow that in humid climates, where the soil is held together by a luxuriant protective mantle of forest and grass land, the rate of new topsoil formation balances the rate of erosion. Even in an arid climate like that which prevails in most of the Colorado River Basin away from the mountains, the accumulation of vegetable litter, the formation of new soil, and the healthy growth of a protective covering of grass originally occurred on almost all slopes and flats. It is true that in the Colorado River Basin the lowering of stream beds and canyon bottoms by natural erosion, and the reduction in size of plateaus and buttes by the weathering and collapse of their vertical-walled perimeters, proceeded at a rate that, geologically speaking, was fairly rapid, when compared with that of some other regions. The top surface of the country also was extensively planed down during the lapse of millions of years. Nevertheless, in terms of year-to-year continuity, the topsoil was healthy, and maintained a wealth of plant cover and animal life in startling contrast to what is found today. Natural erosion originally was no insuperable obstacle to fertility and abundance even in the desert. For example, in the great expanse of sandstone soils of the Little Colorado River Basin, "where the cover of grass, sage, and other low growth has not been disturbed by grazing, erosion is of no importance; but under conditions of depleted vegetation, as a result of overgrazing, sheet erosion, gullying, and wind erosion are active over large areas."  The soil has sickened and commenced to die only after the balance has been disturbed by the coming of the white man.
Man-caused or "accelerated erosion" results when grazing and other agricultural activities strip away the plant cover and allow the wind and water to wear away the topsoil more rapidly than nature ever did. In many places, this living surface layer, product of hundreds of centuries of microscopic accumulation, has completely disappeared, and the land has died within the space of 20 years.  The misconception of those who fail to distinguish between natural and man-caused erosion, imagining that the consequences of the latter are of little importance, is like that of a person who would ignore the fact that his house had caught fire, on the theory that fire always had existed as a purely natural phenomenon.
Franklin Flat, in the San Simon Valley of Arizona, was covered with grassy, flower-spangled meadows in 1882. Grass was stirrup-high along the continuously flowing river, which had practically no banks. In 1895, 50,000 cattle were grazing in the valley. By 1934, as a result of overgrazing, the green meadow cover had been replaced by drifting sand and the river, now an intermittent stream, had cut a chasm through the heart of that once-fertile land. 
Oraibi Wash, once a small stream tributary to the Little Colorado River in Arizona, has been cut by silt-laden, runaway waters into a twisting gully 80 miles long and from 20 to 80 feet deep.  The adjacent Polacca Wash commenced to deepen after 1868, when immense numbers of livestock were crowded upon the newly created Navajo Reservation. Now the wash is dissected by a continuous 90-mile gully from 10 to 50 feet below the valley floor, with great tributary gullies that continually eat into the slopes of Black Mesa. Today, "overgrazing has altered the plant association on the mesa areas of the Polacca Wash drainage and has so increased the run-off that all rains except those of very low intensity cause soil erosion"  Most of the hundred-foot-deep channel in the Jadito Wash has been cut since 1914.
Chaco Canyon had no gully in 1849 and contained a continuous, clear stream. By 1877 an arroyo 16 feet deep and 40 to 60 feet wide had developed. In 1924 this arroyo was 30 feet deep and 200 to 300 feet wide. There is no stream there now except during flash flood. 
The Santa Cruz River did not develop a continuous channel until 1890. 
In 1846, even the Gila River, which, like the Colorado River, receives much sediment from natural erosion, flowed clearer. Its tributaries commenced to erode rapidly only after 1870.
Kanab Creek, in southern Utah, commenced to erode severely in 1883. Three years later a gully 60 feet deep, 70 feet wide, and 15 miles long had been formed.  Formerly timbered slopes on the Chuska Mountains of northwestern New Mexico have been eroded down to bedrock in some places as a result of overgrazing. 
Wind has added its influence to that of water in scouring away the unprotected topsoil. Winds are strong over the Colorado River Basin, but in the early days of settlement, dust storms and whirlwinds were relatively small in scale and infrequent. Trampling hoofs loosened and broke the protective, all-embracing grip of the virgin grass roots. When the plant cover was depleted, the soil dried out and become pulverized. Now the whirling dust columns march across the desert and semi-arid lands of the basin during the spring, summer, and fall months. Finer soil particles are sucked high into the air and sometimes are carried hundreds miles; coarser particles are rolled and skipped along the bare surface, accumulating in drifts when they encounter an obstacle. Dust storms last for days, particularly in the basin of the Little Colorado River, obscuring the horizon. When the wind blows continuously, "blow holes," where the soil lighter or the vegetation scantier, send up such stream of dust from a given spot that from a distance it resembles the billowing smoke of a factory.
Meaning of soil erosion to human welfare.The seriousness of soil erosion to the future of the entire nation has been emphasized over and over again experts, who have ably presented the picture of slow destruction. The dying of the soil is all the more insidious because the first stages often have been slow enough to escape notice from one generation to another. By the time they have speeded up and become conspicuous, complete restoration is usually hopeless. The Soil Conservation Service estimates there are in the entire country some 200 million erosion gullies. These, and the still more widespread sheet-erosion, already have ruined 14 percent of the United States or an area nearly eight times as large as Wisconsin. An additional 35 percent of the land is now threatened.
These facts regarding soil erosion in the country at large help to give some perspective regarding conditions in the Colorado River Basin, where aridity accentuates the problem. In that region,
Obviously this prospect of decline applies also to other soil crops of the region, such as native plants and wildlife.
The Forest Service estimates that it takes one-fifth more range of the tall-grass type to feed a cow now than when the range was first used. On short-grass range, nearly twice as much acreage is needed now; on sagebrush-grass range, more than three times the original acreage; and on salt-desert shrub, three and one-half times the former amount. Continuous overgrazing has changed the whole character of the range, reducing the quantity and quality of the forage and deteriorating the soil itself.  The importance to human welfare in the Colorado River Basin of this reduction in the production capacity of range land may be judged from the fact that grazing outranks all other agricultural interests there manyfold.
Soil washed downstream from the uplands is deposited 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.
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. 
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 climate. This claim is not supported by recent careful investigations. 
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 the comprehensive investigations of innumerable field biologists. Even here, however, the trend is hopeful. Hunting, fishing, and trapping no longer are the principal obstacles to the restoration of wildlife. Land use, or abuse, in relation to the remaining soil and plant cover, will determine the destiny of our native plants and animal life.
Stream pollution.Because of the sparse human population in the Colorado River Basin and the relative scarcity of large industrial establishments, stream pollution is not nearly as serious as in the East. However, mine and mill waste has destroyed large numbers of fish at times,  and still is responsible for the poor quality of fishing in many Rocky Mountain streams.
The recent introduction by man-caused erosion of great quantities of sediment into streams that formerly were clear is a form of pollution. Fish food is destroyed during floods when the moving sand and gravel tear aquatic plants and animals loose from stream beds and grind them to pieces. Silt deposited in stream and lake beds smothers aquatic growth in a manner comparable to the burying and killing of topsoil on land by the deposition of inert layers of flood-borne sediment. Fish may be killed directly when spawning beds are covered by the silt deposits and the eggs smothered. In severe floods the fish often are suffocated by the suspended mud or crushed by the moving masses of rock and gravel. 
Even in the absence of scouring floods, any fine silt or mine sediments that may be suspended in the water are extremely harmful because they shut out the sunlight that is required for the growth of bottom-dwelling aquatic plants. These plants, particularly the microscopic forms, are the starting link in the aquatic food chain in the same general way that topsoil organisms have been shown to be the starting link in the terrestrial food chain.