Ch. 23] DISTRIBUTION OF GULLIES 411 



marked by sudden peaks and rapid recession, the magnitude of flow 

 depending on the intensity and duration of the accompanying rain since 

 there is little vegetation to either impede or decrease the runoff by in- 

 ducing percolation. The headcuts and gully banks remain vertical 

 as a result of sapping and undercutting by these periodic flows. Al- 

 though most of the major tributaries of the San Simon are still uncut, 

 side drainage pouring over the vertical banks, particularly opposite 

 the unprotected barren tracts, has incised literally hundreds of short 

 deep channels and subterranean passages, leaving the terrain next to 

 the bank cut into narrow fingers and isolated blocks of soil. Under 

 these conditions the potential silt contribution to the Gila River from 

 the San Simon Valley is enormous, being limited only by the amount 

 of water available for transportation, since the sediments themselves 

 offer little if any resistance to removal. Typical views of the present 

 condition of the San Simon gully are shown in Fig. 1. 



With suitable modification for differences in length and dimensions 

 of the gully, character of the valley fill, history of gully development, 

 and other details, the picture of the San Simon could be transposed 

 to a myriad of other valleys located throughout the West. The con- 

 trol of these gullies is essentially the major erosion problem of the 

 West. 



DISTRIBUTION OF GULLIES 



Gullies similar to the San Simon, some greatly exceeding it in size 

 and destructiveness, are common throughout the Southwest. In New 

 Mexico the gullied valleys of the Rio Grande, including the Rio Puerco, 

 the Jemez, and the Salado, have been described in such detail and are 

 so well known as to be familiar to those having only a casual acquaint- 

 ance with the erosion problems of the area, but scores of others of al- 

 most equally impressive dimensions also occur in the basin (Bryan and 

 Post, 1937; National Resources Committee, 1938). In the Gila River 

 drainage, the valleys of the Santa Cruz, the San Pedro, the Mangus, 

 and the San Simon represent only the larger of numerous gullied tribu- 

 tary valleys distributed from near the headwaters of the river almost 

 to the mouth. 



Although possibly not so prevalent as in southern latitudes, gullies 

 nonetheless occur in large numbers in the headwater areas of the Mis- 

 souri and its tributaries. Particularly is this true of the Bighorn and 

 Powder rivers in Wyoming. One familiar with these streams will im- 

 mediately call to mind such striking examples as Five-Mile, Muddy, 

 E-K, and Badwater creeks in the Wind River Basin; Fifteen-Mile, 



