REVIEWS 815 



densely backed by grazing previous to the storm, yet the whole of this 

 small watershed was well marked with gullies, due to the storm. The 

 flood water where it reached the mouth of the side canyon presented a 

 front about 8 feet wide and i^ feet high. The water was so filled with 

 sediment that it did not flow, but rolled over and 6ver. In a short time 

 the flow increased to a front of from lo to 25 feet wide and from 6 to 8 

 feet high. Owing to the enormous deposits of debris, the course at the 

 mouth of the channel changed three times during the progress of the 

 storm. 



In order to determine the factors controlling the amount of erratic 

 run-ofT and erosion in 191 2, two areas as similar as possible in topo- 

 graphic, soil, and climatic conditions and in vegetation were selected 

 for study. These areas are at the head of Ephraim Canyon, on the 

 Manti National Forest. There are no permanent streams on either 

 area, run-off occurring only after rain storms and from melting snow. 



Comprehensive studies were made on each of these areas regarding 

 the amount and character of the run-off following the melting of the 

 snow in the spring and following rain. It is shown that erosion from 

 melting snows is a more serious factor than generally supposed when the 

 vegetation cover is sparse and the slope steep or even moderately steep. 

 Out of 26 rain storms for the year 191 5, distributed over the four 

 months from June to September, only one storm produced run-off. 

 During the following year there were several rain storms during the 

 same months, covering a period of two to five days each, which pro- 

 duced run-off. In cases where the rainfall continued after the soil be- 

 came completely saturated, run-off occurred and carried with it a large 

 amount of sediment. In general, the extent of erosion and run-off on 

 the two areas following rains depends upon (a) the rate at which the 

 rain falls, (b) the steepness of the slope, (c) the presence of well-estab- 

 lished gullies, (d) the character of the soil, and (e) the density and 

 character of the vegetation. 



Following the destruction of the vegetative cover by overgrazing at 

 high elevations, wind movement becomes particularly active in the 

 translocation of soil. Investigation of wind velocity at different eleva- 

 tions during the growing season, which is the only time the ground is 

 exposed at high elevations, showed a movement approximately 100 per 

 cent greater in the spruce-fir type at 10,000 feet elevation than in the 

 aspen type, 1,500 feet below. Xot only has the wind greater velocity at 

 the higher elevations, but the vegetation is usually much less dense, and 

 as a consequence wind movement of the same velocity has a much 

 greater effect. It is especially important, therefore, that the vegetable 



