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Prospectors and mine owners often wish to find water in new districts, away from the main lines of travel. In their search for it they must be guided by geologic and topographic conditions and by the vegetation, which is often a useful guide. MOUNTAIN SPRINGS AND TANKS. As a rule the water found at high elevations comes from rocks from alkalies and is pure and sweet. In hunting for these higher springs one must go up to the bare, rocky gulches, above the loose material into which the rain waters sink so readily and are lost. The mountain springs are small and the majority of them disappear during the drier periods, but for a short time after a storm they may be abundant and furnish strong flows. In the lava or granite ranges water from the winter rains often collects in rock bowls. Where these are in the shade and are protected from the wind, water may remain in them for months after a storm. Such natural reservoirs are known as "tanks." After rains may be valuable sources of supply for prospectors, but after a series of long, dry seasons they are not to be depended on. Some of these tanks are of large capacity and are very valuable to mining camps. They are so rare, however, that travelers can not expect to find them in an emergency without knowing their whereabouts or their character. DRY LAKES. In the vicinity of the dry lakes—-the sinks of the desert—-water generally be found by digging or boring wells. These playas are the lowest points in local drainage basins. When the rains in such a drainage basin are heavy enough to induce a surface flow to the depression the waters collect there to sink gradually or to be evaporated. These sinks have no surface outlet, and some of them are rock-floored and have no underground outlet. All of the surplus water of the local watershed is, therefore, impounded in them. Although it may not accumulate at the surface, its quantity is usually sufficient so that comparatively shallow digging will reveal its presence. The supply in such a basin does not depend entirely on the amount of water that reaches the depression over the surface. An important percentage of the lighter rains is absorbed by the debris along the flanks of the desert ranges and percolates slowly through the sand and gravel to the playa. A part of the floods resulting from the rare cloud-bursts and heavier storms is also absorbed in the same way and seeks the lowest point in the basin by passage underground through the pores of the gravel.

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