€4 The Badland Formations of the Black Hills Region 



lateral extent, Concretions are common and these as well as the 

 sandstones accentuate the irregularity of erosion. The bare 

 clay slopes under the influence of occasional rains and the beat- 

 ing suns, generally show a spongy surface, the loosening porous 

 clay often extending to a depth of several inches. This feature 

 is common on the sloping surface of the Oreodon beds and is 

 especially characteristic of the rounded hillocks of the Titan- 

 otherium beds (see Plate 17). This preliminary loosening of 

 the clay, explains perhaps more than any other one feature, the 

 surpassing ease with which the countless tiny channels are 

 formed and how it is that the streams become turbid with every 

 passing shower. 



Any hard layer that may be present tends to resist erosion 

 and this at once initiates surface irregularities. The uncon- 

 solidated clays being more rapidly removed, the harder stratum 

 soon stands out in distinct relief and later by undercutting, a 

 precipice develops. Joints often accelerate the erosion along cer- 

 tain vertical planes and the result is the development sometimes 

 of cave-like excavations and sometimes of columnar masses. 

 Columns are likely to develop also in connection with hard strata 

 made up of concretionary masses. They are especially abundant 

 in the Protoceras beds, where concretionary masses and jointed 

 sandstones are both abundant. 



Generally the transportation lags perceptibly behind the 

 disintegration and as a consequence a thin fan of sediment clings 

 to the base of every pillar, mound or table. The full extent of 

 these alluvial fans is often not fully discerned. Being formed 

 by the conjoint action of many little streams and made up of ex- 

 cessively fine sediment, their surface slope is low and one readily 

 confuses the alluvial materials with the undisturbed beds on 

 which they lie. As may be readily inferred, there is much 

 transient carrying of sediments and much meandering of ma- 

 turer streams. A single season or even a single freshet often 

 makes important changes in a stream's position and there is 

 decided tendency in the medium sized streams to quickly de- 

 velop box-like trenches (see Plate 18). Cheyenne river and 

 White river are active throughout the year, and during the 

 rainy season they flow in large volume, but the tributary streams 

 coming from the badlands are dry much of the time. Some are 

 able to struggle along in continuous flow for a little while after 

 the rainy season, but later in most of them little is left but dusty 

 sands and stingy pools of water, the latter clear if strongly alka- 

 line, otherwise turbid to the consistency of mud porridge. 



