134 



B. SHIMEK PLEISTOCENE OF SIOUX FALLS AND VICINIT'/ 



west side of Sioux Falls. It seems to extend in a westerly direction for 

 some distance. 



Below the western bend of the river the valley is narrow for several 

 miles, its narrowest portion lying in the city of Sioux Falls, where it 

 scarcely exceeds half a mile in width. Above this bend, along the west 

 line of Sioux Falls and northward, the valley widens to more than 2 miles, 

 and the bluffs on either side of the flat bottom land are low and rounded. 

 West of this part of the valley the bluffs rise only about 50 feet above the 

 valley, and the region to the west and northwest presents a gently but dis- 

 tinctly rolling surface. The difference between the parts of the valley 

 above and below Sioux Falls is very striking. 



Another topographic feature of interest is presented by the high 

 benches, with boulder slopes, which may be seen along the narrower part 

 of the valley as far down as East Sioux Falls, and also along the valle3's 

 which cut the upland between Sioux Falls and East Sioux Falls. These 

 benches rise to be about 130 feet above the river below the falls, and are, 

 usualW capped with a layer of gravel and boulders, or sometimes silt. 

 Where boulders strew the slopes of these benches, as shown in plate 8, 

 figure 2, they are apparently derived from the capping stratum. These 

 benches are most prominent east of Sioux Falls and north of East Sioux 

 Falls. 



The valley of the river also presents several features of interest. Xo 

 doubt the chief of these are the gravelly and bouldery terraces, which are 

 very striking and which often closely crowd the river, so that its imme- 

 diate valley is very narrow. This immediate valley is frequently bor- 

 dered by alluvial deposits, consisting of silt and sand, with numerous 

 shells of modern fresh-water mollusks. 



On the Iowa side the most prominent terraces or benches are those at 

 Granite and Klondike. The Granite terrace rises 40 to 50 feet above the 

 Big Sioux bottoms, and is cut in its southern part by Bloody Eun and by 

 the Chicago, Eock Island and Pacific Eailway. It does not follow the 

 valley of the creek, though small terraces are found, and the valley is 

 much broader above Granite than it is just below, where it enters the 

 great terrace or bench. It appears quite flat, but its surface is broken by 

 mostly shallow drainage channels. That part of it which lies north of 

 the railroad and from one to one and a half miles west of Granite has its 

 surface varied by about 100 boulder aiid gravel covered mounds, which 

 average about 5 or 6 feet in height and 50 feet in diameter. Two of 

 these are represented in plate 9, figure 1. Wilder (1900, page 140) 

 ascribes to them a morainic origin, but they are clearly burial mounds or 



