26 BULLETIN" 6T5, TJ. S. DEPARTMENT OF AGRICULTURE. 



conclude that the change in the ratios of run-off and erosion showing 

 a marked increase in erosion on area B was due to grazing. Instead 

 of a large proportion of the rain being absorbed, the soil surface on 

 area B was so hard-packed by the trampling of the stock that the 

 run-off was appreciably increased. Much of the sediment deposited 

 was carried directly from the gullies, a large amount of loose dirt 

 having been worked into these depressions as the sheep traveled 

 over them. 



The example of increased erosion due to grazing as given on the 

 selected areas under date of August 5, 1916, is merely an exact meas- 

 urement of a condition which has been observed in many other cases. 

 Excellent examples of results of varying intensity of grazing and of 

 protection of the lands from stock have been observed on two ad- 

 joining watersheds on the Manti Forest. Until 1904 Manti Canyon 

 flooded oftener — and the floods did more damage — than perhaps any 

 other canyon on the entire Forest. From 1904 to 1917 this canyon 

 has been grazed very lightly by cattle, while the adjoining canyons 

 have been grazed fairly heavily each season. Though there is still 

 abundant evidence of past erosion and innumerable gullies at the 

 head of the Manti watershed, the gullies have rounded out and the- 

 soil, having assumed an angle of repose, now supports a stand of 

 grass and weeds. The fine soil, with its increased organic matter, is 

 so loose and mellow that a saddle horse sinks into it over his hoofs. 

 At the head of Becks Canyon, 3 miles north of Manti Canyon, 

 sheep have grazed each year. Instead of a loose soil it is hard- 

 packed, the gullies are relatively deep and V-shaped instead of 

 rounded, and they support practically no vegetation either on the 

 sides or bottom. Each of these watersheds has been under observa- 

 tion during various rainstorms and the amount of precipitation re- 

 ceived at the head of each canyon has been recorded by means of rain 

 gauges. A rainstorm that is completely absorbed without surface 

 run-off on the Manti drainage often produces innumerable muddy 

 rivulets in a few minutes on the Becks Canj^on drainage. It would 

 take a very heavy rainstorm — considerably heavier than has oc- 

 curred during the past eight years — to produce a flood in Manti Can- 

 yon. From Becks Canyon, on the other hand, floods have occurred 

 as a result of 0.55 of an inch of rainfall; several floods have origi- 

 nated in this canyon during the past few years. 



Another instance showing the relation of grazing to erosion and 

 floods occurred August 2, 1912, in Twelve Mile and Willow Creek 

 Canyons. A committee of sheepmen, cattlemen, and Forest officers 

 -who were inspecting the range in Twelve Mile Canyon on the day 

 of the storm Avhich occasioned the flood testified that these floods 

 came from mountain areas adjoining the Manti Forest which had 

 been used as lambing grounds for several successive years. The ob- 



