The Dakota sandstone and the overlying dense plastic shales form the most remarkable artesian basin in the United States with respect to its great extent, the long distances through which its water has percolated from the outcrops of the sandstone in the western mountains to the areas of artesian flow, and especially the tremendous pressure under which the water in the sandstone was originally by thick and continuous cover of impermeable shales. In 1882 a well was drilled to the Dakota sandstone at Aberdeen, S. Dak., by the Chicago, Milwaukee & St. Paul Railway Co. This well was reported by Nettleton1 to have been "the first bore put down which reached the artesian basin of the Dakotas." In 1896 Darton2 estimated that about 400 artesian wells had been drilled to the Dakota sandstone, presumably in South Dakota and adjacent parts of the artesian basin in North Dakota which he investigated.3 The strongest of these wells had pressures ranging from 100 to more than 200 pounds to the square inch and flows ranging from 1,000 to more than 4,000 gallons a minute.
The present brief paper is based chiefly on the data that have been obtained in the successive surveys in regard to about 230 artesian wells in or near the Edgeley quadrangle. A table of these well data is on file in the United States Geological Survey and is to be published in the detailed report on the geology and hydrology of the Edgeley and La Moure quadrangles that has been prepared by Mr. Hard. The well data obtained by Mr. Hard have already been published in a report prepared by him in his capacity as State flood-control engineer.
