THE BAD LANDS OF SOUTH DAKOTA 



By N. H. Parton, 

 U. S. Geological Survey 



There are Bad Lands of greater or less' area in various portions 

 of the arid and semi-arid districts of the west. The most exten- 

 sive tract is in the southwestern part of South Dakota, on White 

 river, a short distance east of the Black hills. They begin near 

 the 101st meridian and extend for about 120 miles up the White 

 River valley, nearly to the Nebraska line. Their width varies 

 from 30 to 50 miles and their total area is about 4 000 square 

 miles. They attain their finest development on the north side 

 of the valley, along the divide between White river and the 

 south fork of the Cheyenne river. This divide is high and nar- 

 row, and is composed of the light colored clays — of the White 

 River formation — and is a region of slight rainfall. 



The principal factors in bad-land development here are mass- 

 ive structure of the moderately hard clay and the steep decliv- 

 ities which, together, afford exceedingly favorable conditions for 

 rapid erosion. Somewhat similar conditions prevail on the 

 south side of the White River valle3 r . The region was originally 

 a relatively smooth plain. It was uplifted in a recent geologic 

 time, and as the White river and the south fork of the Cheyenne 

 river deepened their valleys during the progress of this uplift, 

 they and their branch streams cut deeply into the surface of the 

 plains. As erosion progressed, portions of this surface have 

 been sculptured into narrow ridges, steep-sided buttes, rounded 

 domes, pinnacles, and castellated forms in endless variety. Por- 

 tions of the plains remain as grass-covered table-lands, usually 

 bounded by high, rugged cliffs of cla3 r , and deeply channeled 

 by intricate winding canons. As erosion is more rapid than soil 

 formation, the slopes are bare and their prevailing tints are flesh, 

 cream, ashy gray, pale green, and buff. The material is fairly 

 homogeneous in its texture, but owing to slight differences in 

 texture, it is carved and channeled into great variety of forms. 

 Occasionally thin beds of sandstone and beds of slight^ harder 

 clays add to the complexity of erosion products. The lower beds 

 of the formation are filled with thin vertical veins of chalcedony, 



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