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Show The date and the extent of terracing in the San Juan country are duplicated in canyons south of the San Juan, west of Glen Canyon, and generally through Arizona, New Mexico, and southwestern Colorado. The channeling that produced the terraces may be the result of climatic changes, of uplift, or of these two agencies combined. The immediate cause is overgrazing. With the destruction of the pro- tective vegetation the runoff became spas- modic, and the streams were intermittently given power to remove canyon fill. The area supplying Silver City, N. Mex., with water is another case. From about 1870 to 1908, the watershed was subjected to abuse; fires and fuelwood cutting denuded the area of tree growth, grazing animals ate the forage to its roots. The watershed was eroded with great gullies over the whole area. The creek that ran through the town from the area began to scour, and the main street became a gully 15 to 40 feet deep, from 75 to 200 feet wide, and a mile long through the town. The water supply dwindled rapidly and wells failed. Beginning about 1908, the area was put under administration: wood cutting and fires were stopped, livestock numbers were sharply re- duced. Later, a more intensive management plan was adopted; all stock were removed, trees planted, grasses reseeded, small check dams were built in the gullies, and the area fenced. The area is completely revegetated and the soil is stabilized. Floods no longer roar through the city. The gully along the main street is healing. Under- ground water supply has increased. City wells that once could barely supply 75,000 gallons of water daily, now yield 200,000 gallons without depletion.42 Bisbee, Ariz., has a somewhat similar situation and comparable results from better watershed man- agement. Other cities now exercising control or management of their municipal watersheds include Miami, Globe, Prescott, and Safford, Ariz. Live- stock control was the initial measure, followed by the rehabilitation of the cover.48 That such instances are not rare is indicated by the fact that when similar measures are applied comparable results are obtained, as in the Steam- boat Canyon area in the Navajo Reservation. This area in the San Juan River drainage was one of seven depleted and eroded areas chosen in 1934 ** U. S. Forest Service. ** Soil Conservation Service. for demonstration purposes. Livestock numbers were reduced to the capacity of the forage, and land management practices were instituted. Sup- plementary minor engineering measures supported the reseeding and revegetation program. The vigor, growth, and density of the forage have made marked recovery. Except in the first 3 years after the area was placed under management, the total weight of livestock produced has been greater than before management, even though a smaller number of animals was grazed on the area. An outstand- ing result has been the reduction in erosion and flood flows. Prior to treatment, the area produced mud flows as flash floods. These contained up to 75 percent of sediment by volume. Since treat- ment of the area these flash floods have been greatly reduced, and erosion is negligible.44 That supplemental upstream or headwater en- gineering measures also function in reducing erosion is shown at the Navajo Indian Experiment Station near Gallup, N. Mex. Here a detailed study of nearly 10,000 acres showed that arroyo cutting can be stopped. Other operations took the water from the gullies and spread it over the land surface, greatly stimulating forage production. As a result there was almost 100 percent sediment control, keep- ing 500 acre-feet of sediment or 3.75 acre-feet per square mile annually out of the San Juan River.45 Numerous demonstrations on other public lands show that proper handling of the public range will bring about revegetation and the reduction of ero- sion. Considerable recovery has been obtained on the national forests through livestock reductions brought about by delays in the opening date, shorter seasons, closures of certain areas to use, and in re- ductions of numbers. On these areas the live- stock decrease in Arizona, for example, has been about 2 percent a year for the past decade. Al- though the trend in range condition on 26 percent of the range allotments is upward today despite the droughts of the past several years, there is much room for improvement. This is shown by the fact that the range on about half of the allotments is still retrogressing, and that on about 16 percent it shows a decidedly downward trend. The Mesa Verde National Park was once just a portion of the overgrazed, bare, and eroding public u Even L. Flory, Indian Service. Proceedings, Federal Inter-Agency Sedimentation Conference, 1948. * D. S. Hubbel and J. L. Gardner, Effects of Diverting Sediment-Laden Runoff Water to Crops and Range Lands, 1945. Also Carl B. Brown, Proceedings, Federal Inter- Agency Sedimentation Conference, 1948. 423 |