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National Geographic : 1905 Aug
Contents
THE CENTRAL GREAT PLAINS Part of the surface water passes into the sandstones in their elevated outcrop zones along the foot of the western mountains and flows east through the permeable rocks, in most cases finally escaping in springs in the low-level areas of outcrop eastward and southward. In such water-bearing strata as the Dakota and underlying beds, which are overlain by a thick mass of impermeable deposits, the waters are under great pres sure, for the intake zone has an altitude of from 4,000 to 6,000oo feet and the region of outflow is only from I,ooo to 1,200 feet above sea-level. The existence of this pressure, as found in many wells in eastern South Da kota, is the strongest evidence we possess that the waters flow underground for many hundreds of miles. Several wells show sur face pressures over 175 pounds to the square inch and two are slightly over 200 pounds, the latter indicating a pressure of 780 pounds at the bottom of the well. In South Dakota the Da kota sandstone carries a large volume of water, which has been extensively utilized by artesian wells. This water is under pressure so great that in the eastern portion of the state flows are obtainable in all but the very highest lands, except in the southeast corner, near the zone, where the head is lost by the sandstone reaching the surface. Over a thousand deep wells have been sunk east of the Missouri River, most of which are from 500 to i,ooo feet in depth and generally yield a large supply of flowing water, much of which is used for irrigation. The aggregate flow from these wells is esti mated to be about 7,000,000 gallons a day. The illustration on page 389 shows a remarkable well. Another phenomenal well in the same state is a well at Spring field, which has a flow of 3,292 gallons per minute, although its closed pressure is not so great as that of many other wells in the state. It furnishes power for a 6o-barrel flour mill by day and for From N. H. Darton, U. S. Geological Survey Pulpit Rock, Kansas An outcrop of Dakota sandstone an electric-light plant by night. For a while it threw sand, and when this finally ceased the flow was thought to have slightly decreased. It is believed by some persons that owing to this great draft upon the re sources the available supply is dimin ishing, but there is as yet no valid evi- 391
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