The Central Great Plains 



39 1 



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 6,000 

 feet and the region of outflow is 

 only from 1,000 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 

 1,000 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 60-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- 



