Ch. 23] REFERENCES 433 



to be enlarged. If it can be shown that these periods were not local in 

 extent but affected widespread areas simultaneously, and that they 

 were related to some common cause such as increasing aridity of 

 climate, of which the present might be an example, a long step will have 

 been taken in formulating a plan of erosion treatment. As the record 

 of the changes must be read from the sediments themselves, new tech- 

 niques and standards for recognizing and evaluating the evidence must 

 be developed. One urgent need at present is a method for determining 

 the relationship between climate and the character of sediments de- 

 posited during a given period. Another is for criteria that can be 

 used in interpreting climate by the evidence of alteration in the sedi- 

 ments since deposition. Each is fundamental in finding the causes 

 of past changes in valley history. 



Because vegetation is so closely allied to the erosion problem, the 

 need for research, not only on its relation to sediment transportation 

 but also on means of propagating vegetation, are evident. Among 

 the pertinent questions are: What is the minimum density of various 

 types of cover required to prevent erosion on the many different soils 

 and slopes commonly found in western desert valleys? What minimum 

 density is required to induce deposition under the same conditions? 

 Is the normal precipitation in the area sufficient to maintain this den- 

 sity with or without grazing use? If not, what feasible measures, if 

 any, including both engineering structures and changes in land-manage- 

 ment practices, can be taken to insure protection of the most vul- 

 nerable localities? 



These suggestions touch only broad phases of the research needed be- 

 fore the critical erosion problem of the West, of which gullying is the 

 most prominent feature, can be approached with any hope of success- 

 ful solution. The prosecution of this research will necessitate detailed 

 inquiry into the many interrelated aspects of erosion, each of which will 

 involve long, arduous, and expensive effort before the final answer is 

 obtained. 



REFERENCES 



Albritton, C. C, Jr., and Bryan, K. (1939). Quaternary stratigraphy in the Davis 



Mountains, Trans-Pecos, Texas: Bull. Geol. Soc. Amer., vol. 50, pp. 1423-1474. 

 Antevs, E. (1948). The Great Basin with emphasis on glacial and post-glacial 



times: Bull. Univ. Utah, vol. 38, No. 20, June 1948, p. 12. 

 Bailey, R. W. (1935). Epicycles of erosion in the valleys of the Colorado Plateau 



province: Jour. Geol., vol. 43, pp. 337-355. 

 (1937). Watershed symposium: Jour. Forestry, vol. 35, No. 11, Nov. 



1937. 



