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Show Valley, a tributary of the Paria, was among the latest areas in southern Utah to be converted into cattle ranches, but since 1915 a new channel in the valley fill, 40 and more feet deep, has cut through half the length of the valley, destroying shallow lakes and meadows.89 Paria, Utah, on the Paria River about 50 miles above its junction with the Colorado, is an example of a once prosperous community destroyed by ac- celerated erosion attributable to land abuse. The town was settled in 1874. By 1884 the population included 107 resident members of the Church of Latter Day Saints (Mormon), in addition to non- resident cattlemen and about 20 Piutes. Prosperity came to a sudden end in 1885. Floods in 1883 were followed by the un- usually severe winter of 1883-84 and by more floods in the summer of 1884, which washed away farmhouses and fields and converted the narrow stream channel into a wash that ex- tended in places from rock wall to rock wall. Except for a few acres protected downstream by rock buttresses, all the arable lands dis- appeared. In the spring of 1884 Paria had its maxinaum population. In September of that year 48 people remained, and in 1885 the Paria ward was disorganized. For the last 40 yea.rs the removal of soil and alluvial banks has continued until the amount of usable land probably does not exceed 60 acres. This area supports in part the two or three families who live at Paria during the planting and harvesting seasons.40 An example from the San Juan drainage illus- trates the channel cutting and sedimentation that have occurxed since settlement: 41 The typical tributary to the San Juan and the Colorado flows between alluvial terraces within rock-walled canyons. The canyon fill of a previous cycle has been cut into flat- topped, steep-faced segments by streams of the present cycle. In making terraces the streams have h>een effective in accordance with their " Walter E». Cottam, University of Utah Bulletin, vol. 37, No. 1, February 19, 1947; Reed W. Bailey, Proceed- ings, Federa.1 Inter-Agency Sedimentation Conference, 1948. ^ Herbert E. Gregory and Raymond C. Moore, The Kaiparowits Region, Professional Paper 164, U. S. Geo- logical Survey, 1931. 41 Herbert 3S. Gregory, The San Juan Country, Profes- sional Paper 188, U. S. Geological Survey, 1938. size, their gradient, the width of their floors, and the number of violent showers that fall within their drainage basins. In general the terraces are increasing in length by headward erosion and in height by down-cutting, but all stages of development are represented. v In some places the two terraces that border a stream are separated by a narrow vertical trench; in other places they are far apart and may even appear as flat-topped embankments pressed close against opposing canyon walls. In places the terraces are absent and the orig- inal canyon fill remains intact or has been so completely removed that the position of the terrace is indicated only by patches of sand that cling to the canyon wall, and its height by a band that separates zones of unequally weath- ered rock. In parts of their courses some streams have cut entirely through the alluvium and into the rock below. As down-cutting and undermining are more rapid than surface weathering, the fronts of most terraces are vertical. To climb these walls of crumbling sand is no easy task. To find a place where their tops can be reached, pack trains may have to travel many miles. The construction of these terraces in- volves erosion on a large scale. For example, the amount of fill removed in a typical 1-mile stretch is estimated as 1 million cubic yards for Grand Gulch, 800,000 cubic yards for Cotton- wood Canyon, and 650,000 for Butler Wash. North of Wilson Mesa, a canyon 6 miles long, 160 to 200 feet wide, and once filled to a depth of nearly 80 feet, has been entirely stripped of alluvium. It seems reasonable to assume that the time consumed in tearing up and transporting such great quantities of sand, gravel, and silt from hundreds of canyon floors would be measured at least by centuries, but nearly all the terraces have been formed during the last 50 years, many during the last 10 years, and each year adds to their number. In place of the present wide washes floored with sand moved about by ephemeral streams and bordered by flat-topped banks of alluvium, the pioneers of 1880 found "broad fields," "meadows," "clear streams flowing through willows and alders," "cane swamps," "little ponds," "canyons floored from wall to wall with level, fertile fields." The Piutes say that the trouble began with the coming of the white man. 422 |
