THE SAND-HILL KEGION". 9 



which occupies the northwest corner of the State, is not clearly- 

 defined, since the Arikaree formation, which is the foundation of the 

 Pine Ridge, outcrops within the sand-hill area, notably along the 

 Niobrara, Snake, and north side of the Platte Rivers. The absolute 

 elevation of the sand hills is 1,900 feet at the east and 3,900 feet 

 at the west end. Their elevation, however, is not appreciably greater 

 than that of the surrounding land of other formations. 



The Kansas sand hills are much less extensive. They occupy a 

 strip of ground from 5 to 30 miles wide on the south side of the Arkan- 

 sas River, from the west boundary of the State eastward to the vicin- 

 ity of Great Bend and Hutchinson. At the eastern extremity, how- 

 ever, these hills are not strictly dunes, but are agricultural in char- 

 acter, and hence hardly come within the category of true sand hills. 

 A second strip of sand hills is found south of the Cimarron River, m 

 southwestern Kansas, and is even less extensive than the first. The 

 total area of sand hills in Kansas is about 1,500 square miles, or not 

 more than one-fiftieth of the area of the State. Their elevation 

 increases from east to west and is from 2,500 to 3,500 feet. 



Of the entire area of Kansas and Nebraska it is safe to say that 

 fully 15,000 square miles, or nearly 10 per cent, are sand hills not 

 fitted for agriculture, and therefore of greatest value as forest lands. 

 These areas lie in the semiarid belt, mainly west of the one hundredth 

 meridian, where the rainfall is generally less than 22 inches per 

 annum. 



ORIGIN AND STRUCTURE. 



The Nebraska sand hills have undoubtedly been formed ^ by the 

 breaking down of the Arikaree, a Tertiary sandstone which still 

 exists in the Pine Ridge and in various 'toadstool parks" in the 

 western and northwestern counties, and which outcrops along the 

 Niobrara, Snake, and North Platte Rivers. The sand has been 

 moved to the eastward by the action of wind and water, principally 

 the former, forming a layer from a few feet to several hundred feet 

 thick above the Pierre shale which xmderlies the entire region. This 

 action has been very recent, in fact, has hardly yet ceased, and to 

 some extent, as in Custer County, the sand has covered the loess, or 

 heavy clay-loam soil, which is also a recent formation. There is little 

 evidence of the direct action of water in bringing this sand eastward. 

 Probably the Niobrara has had a very potent influence in its imme- 

 diate vicinity, but most of the sand must have been carried from this 

 stream to the southeast by wind, or to the eastward by some large 

 stream which does not now exist, in the southern part of the region. 



The Kansas sand hills have been similarly formed, but with mate- 

 rial of different origin. Those near the Arkansas River, ^ and probably 



1 Nebraska Geological Survey, Report of the State Geologist, 1903, voL 1. 



2 Soil Survey of the Garden City Area, Bureau of Soils, U. S. Dept. of Agriculture, 1904. 



63519°— Bull. 121—13 2 



