PHYSIOGRAPHY OF BISHOP CONGLOMERATE 625 



slopes unprotected by vegetation, loosen and bring down heavy 

 loads of debris, which the streams, on account of their intermittent 

 character and the rapid dissipation of the water after a shower by 

 evaporation and absorption into the dry soil, are unable to carry 

 out of the valleys. The result is the silting up of the valleys and 

 the formation of alluvial fans and wash-aprons on the slopes. On 

 the return to a moister climate the streams become permanent, the 

 land is protected by vegetation, hence furnishes less debris to the 

 waters of a passing storm, with the result that the wash-aprons and 



Fig. 9. — Sketch showing conditions along Salt Wells Creek. This sketch shows 

 all the terraces referred to in the text, and their relations to each other and to the 

 Miller Mountain plateau. Vertical scale exaggerated. 



silted valleys built up under arid conditions are dissected, leaving 

 gravel terraces along the stream courses. 



3. Erosion. — Following the preceding stage of desiccation and 

 aggradation there came one of erosion when the wash-aprons were 

 dissected by the streams and the gravel and silt deposited in the 

 central part of the valley were cut down, leaving remnants as fiat- 

 topped terraces on either side. This feature is best shown along 

 Salt Wells Creek from the junction of Pretty Water Creek to 

 Chimney Rock, about two and one-half miles to the north. There 

 a cut from one-fourth to one-half mile wide has been made through 



