Ch. 23] PRACTICAL ASPECTS 413 



Thousand Springs Creek in northeastern Nevada and Snake Creek in 

 western Utah, have, in parts of their drainage area, developed gully 

 systems that rival those existing in more humid areas. The fact that 

 both cutting and the concurrent deposition in these remote areas affect 

 only low-value lands accounts for the lack of attention thus far ac- 

 corded the areas. 



PRACTICAL ASPECTS OF THE GULLY PROBLEM 



The above review of the widespread prevalence of gullying is pre- 

 sented to emphasize that the phenomenon is not limited to any one 

 locality or governed by any set of conditions relative to topography, 

 geology, soils, or climate; it is obvious that, throughout this vast area, 

 wide and contrasting variations in these features must occur. Moun- 

 tain valleys, with slopes ranging up to one or two hundred feet per 

 mile, exhibit the same gully characteristics as do others with slopes of 

 only 10 to 15 feet per mile. And, although as noted, gullies are some- 

 what more prevalent in areas such as the Colorado Plateau and por- 

 tions of the High Plains and Rocky Mountain provinces, where the 

 valley fills are derived from surrounding friable sandstones and shales, 

 they also occur in almost equal numbers in southern Arizona and other 

 localities where the alluvium originates from mountains composed of 

 igneous, volcanic, or highly indurated sedimentary and metamorphic 

 rocks. Dimensions and shapes of the valleys likewise appear to have 

 little influence, for the small fan-shaped basin with limited drainage 

 area commonly may be as deeply and extensively incised as its larger 

 elongated counterpart. 



Although trenching and the destruction of land within the affected 

 valleys constitute a serious phase of the problem, because the attack 

 is aimed directly at the more productive portions of the range, this as- 

 pect is possibly of less importance than the disposition of the removed 

 silt. The few figures, such as the previously mentioned survey of the 

 San Simon and a similar estimate by Bryan and Post (1937, p. 86), 

 which shows that nearly 400,000 acre-feet have been removed from the 

 main and tributary channels of the Rio Puerco, are significant only as 

 indicators. Were the surveys extended to cover all the hundreds of 

 other major gullies, aggregating thousands of miles in length, an even 

 more disturbing picture would be revealed. Except where silt from 

 these valleys is deposited without damage on low-value lands within 

 interior basins, it enters and becomes the serious sedimentation prob- 

 lem of the major streams. Thus the problem has a dual aspect: de- 



