Topography near sioux falls IS.*^) 



Special emphasis has here been placed on that portion of the area along 

 the Big Sioux River between Iowa and South Dakota, because specific* 

 references have so often been made to its special topographic features in 

 determining the location of a part of the so-called Altamont moraine. 

 However, the region in the immediate vicinity of Sioux Falls is of equal 

 interest. 



The Big Sioux Eiver here forms a great double bend, first passing 

 southward west of the city, then abruptly turning northeastward through 

 the city to a point about 3 miles north of west from Brandon, and again 

 abruptly turning east and then south to the northwest corner of Iowa and 

 southward. 



These striking deflections from the general southerly course of the 

 stream are due to prominent topographic features of special interest. As 

 previously noted, the ridge opposite Granite, which has been mapped as a 

 part of the Altamont moraine, extends in a northerly and northwesterly 

 direction toward Sioux Falls. Its northerly portion consists of an ele- 

 vated plateau, more or less broken in the ordinary manner of rougher 

 Kansan surfaces, and terminates in a series of ver}^ rugged ridges and 

 knobs northeast of Sioux Falls in the eastern lobe of the double bend. A 

 portion of this rough area is illustrated in plate 8, figure 1. The greater 

 part of this plateau reaches an altitude of nearly 150 feet above the val- 

 ley, but its most rugged portion northward rises fully 220 feet above the 

 river. 



The roughest portion, lying in and near the northeast corner of town- 

 ship 101 north, range 49 west, consists of a bewildering maze of sharp, 

 mostly gravelly, ridges and knobs separated by deep ravines. Its 

 northern and northwestern borders are very abrupt, as shown in the fig- 

 ure, but southward and southwestward it gradually merges with the less 

 broken general surface of the plateau, or broad ridge, which passes around 

 the south side of the western bend of the Big Sioux Eiver. 



Northward from the very rough area north of the river the uplands 

 appear to be somewhat lower, but the surface is broken in characteristic 

 Kansan fashion, and a portion of this topography is projected southwest- 

 ward into the western lobe of the great bend in the form of a narrow 

 ridge, which passes through the city of Sioux Falls, as shown on the 

 map. 



South of the western bend of the river there is a broad ridge, extend- 

 ing westward and here forming the bluffs of the river, which is also more 

 or less broken. Some parts of it rise nearly 150 feet above the river 

 above the falls. This ridge was followed only to a point south of the 



