380 Geology of Artesian Basin in South Dakota. 



THE GEOLOGY OF THE ARTESIAN BASIN IN SOUTH DAKOTA. 



D. S. McCaslin. 



The artesian basin in South Dakota comprises an area vari- 

 ously estimated from 15,000 to 20,000 square miles. Its bounda- 

 ries are not yet fully made out. It certainly extends from Yank • 

 ton to Devil's Lake. Its eastern limits are marked by an irregu- 

 lar line running north and south, at a distance ranging from five 

 to fifty miles east of the James river. Its western boundary is not 

 yet defined. Its probable extension beyond the Missouri river 

 is one of the strong conclusions of all the investigations, though it 

 is doubtful if volume and pressure continue as great as we go 

 toward the Black Hills. As yet no well has been put down west 

 of the Missouri, except at Fort Randall which lies so far south 

 and east that it has no practical bearing on the question of the 

 western limit of the artesian basin. 



The topography of this region is very simple. The James 

 river lies in a broad valley of erosion from 50 to 60 miles wide, 

 lying at an altitude above the sea ranging from 1,408 feet at 

 Jamestown to 1,196 at Yankton. The railway track at Huron is 

 1,287. This would be about the average elevation of the valley 

 through which flows the longest unnavigable stream in the world. 

 From source to mouth, about 250 miles, yet its vermicular chan- 

 nel winds through more than 700 miles in persistent sinuosity. 

 The present river is a mere trickle of the ancient flood that poured 

 down this valley. The canal-like channel simply moves from 

 side to side in a sluggish flow over an alluvial bed. Its banks 

 vary from lacustral sedimentary deposits in Brown county, to 

 bluffs of glacial drift, as in Beadle and Spink counties, till capped 

 with modified drift in Beadle, Sullivan and Sanborn counties, the 

 same covered with loess deposits as at Mitchell and southward. 

 To the east or west of this river the altitude increases. At Arling- 

 ton, about 45 miles east, it is 1,850 feet or 563 feet above level 

 of Huron. At Highmore, aboiit the same distance west, it is 

 1,890, or 603 feet higher than the James river. This outlines a 

 great valley whose depression, by the way, bears no relation what- 

 ever to the artesian water. The water lies practically at the same 

 level everywhere, as we shall see further on, and the differences 

 of altitude only after the depth of the wells and not the deposit 

 of the water. As I have intimated, the whole region is covered 

 with drift deposits. But they are varied in character and distri- 



