412 peterson. PROBLEM OF GULLYING [Ch. 23 



Cottonwood, and Dry creeks in the Bighorn Basin; and Mispah and 

 Pumpkin creeks and Little Powder River in the Powder River Basin. 

 These are but a few among many. Milk River in the north has a 

 similar, though perhaps smaller, quota, the Willow Creek gully (some 

 25 miles in length and averaging approximately 20 feet in depth and 

 100 feet in width) being a prime example. Tributaries of the North 

 Platte River, draining from Casper Mountain in central Wyoming, 

 exhibit a network of gullies seldom duplicated in other localities. 



Parts of the Columbia River Basin are likewise checked with the tell- 

 tale gully scars. The greatest development has already occurred in the 

 semi-arid wastes of eastern Oregon and Washington, but many valleys 

 in Idaho and northern Nevada show evidence of the same action. 



Probably the most advanced and critical development of gullying is 

 found in the Colorado River Basin. Examination by the Inter-Moun- 

 tain Forest and Range Experiment Station (Bailey, 1937) reveals that, 

 of the 115 major tributaries of the Colorado and Green rivers above 

 Lees Ferry, 111 have been trenched by gullies. The combined total 

 length of these channels and their associated tributaries is thousands 

 of miles, and the material removed in these excavations probably ag- 

 gregates hundreds of thousands of acre-feet. Stevens (1936, p. 1254) 

 and Stabler (1936, p. 281) have focused attention on the paradoxical 

 position of the Colorado Plateau in regard to silt and water contribu- 

 tion to the Colorado River. The Plateau area, comprising about 

 65,000 square miles, or 45 percent of the drainage basin of the Colorado 

 above the Grand Canyon, contributes less than 10 percent of the water 

 but more than 75 percent of the silt entering the stream. Practically 

 every valley within the area is gullied. 



Tributaries of the Colorado entering below the Grand Canyon, in- 

 cluding the Bill Williams River, Meadow Valley Wash, Virgin River, 

 and Kanab Creek together with most of their tributaries, present the 

 same picture. Even valleys which at present make no pretense of pos- 

 sessing creeks or rivers (these terms are used in the optimistic sense 

 peculiar to the West, and one must be on the spot at the proper instant 

 even to glimpse the flow of water) have not escaped being gullied, as 

 evidenced by the spectacular trenches found in the lower reaches of the 

 Sacramento and Bouse valleys located in some of the driest parts of 

 western Arizona. 



An examination of numerous tributaries of some of the large Great 

 Basin streams, such as Bear River in Wyoming and Idaho, Sevier 

 River in Utah, and the Humboldt, Truckee, and Walker rivers in 

 Nevada, reveal the same pattern of gullying. Even smaller streams 

 that drain some of the driest parts of the Basin, as, for example, 



