11ANGK PKESKKVATIOIM AND EROSION CONTROL. 



rim of the Wasatch divide, where fa*n-shaped drainage basins are 

 characteristic. 



Practically all the torrential floods which are responsible for the 

 most serious destruction of property originate near the heads of the 

 watersheds, usually at high altitudes. On the Manti Forest the most 

 vital part of the watershed is that lying between altitudes of about 

 9,000 to 10,500 feet, within what is known as the spruce-fir type. 



N 1 Ml Yarrow-Meedlegrass-Cinquefoil ' 9. 



\-//\ Yarrow- DouglasKnotwood (Semt-borren) \ 



f=^ Adder's toncjue-Larkspur-SweeTSage 



Currant- Gooseberry -Yarrow 

 fcy«\ B/uegrass-Wheargrass-Needlejprass (S&mi-Scabland) 

 ES^ G/anf Larkspur -Blue foxg/ove-Dou<jlasKnotwood 

 §^ Yellow brush- Sneer Saye-PeeVme 

 IEEE Spruce 

 ^^ Elder 

 ~ — * Dry rills 



Fig. 1. — Erosion areas A and B, head of Ephraini Canyon, Manti National Forest, Ftah. 



It is on these elevated lands that the rainstorms are the heaviest and 

 most violent, the slopes are steepest, and conditions in general most 

 favorable to erosion. 



The greater part of this upper mountain region consists of large 

 fan-shaped basins which drain through narrow canyons into the 

 valleys below. These canyons are relatively short and have a steep 

 grade. Ephraim Canyon, for example, has an average grade of about 

 22 per cent, or approximately 1,160 feet to the mile. So rapid is 



