Introduction 



As the uses of forest lands increase, the necessity to develop less favorable ter- 

 rain also increases. It also becomes more difficult and complicated to provide access 

 that is both economical and safe from contributing to watershed damage. 



Because of the increased and justified emphasis upon environmental degradation, 

 proper use of the many millions of acres of forest watersheds requires careful planning. 

 The skills of many disciplines and the combined knowledge that covers all aspects of 

 this complicated ecosystem--the forest--are necessary to assure proper use of forest 

 lands. The silviculturist , ecologist, hydrologist, engineer, and others, must all 

 function as a team to develop and carry out plans for management of forest lands. 



The Idaho Batholith (fig. 1) is one of the most critical areas as to surface and 

 subsurface stability (i.e., erosion and landslides) in the Intermountain West; also, 

 this area provides prime spawning and rearing grounds for the Pacific salmon, good 

 timber-producing land and outstanding recreation opportunities. Two major spawning 

 rivers are the South Fork of the Salmon and the Selway Rivers . 



The Batholith contains some of the most rugged and pristine scenery in America and 

 includes such well-known areas as the Selway-Bitterroot Wilderness Area, Salmon River 

 Breaks Primitive Area, and the Magruder Corridor. In such areas, those who are charged 

 with the responsibility of multiple use land management face their most serious and 

 complicated challenges. Within the scope of present knowledge and technological skill, 

 proper planning can assure many uses for much of this vast land area. However, much of 

 the Batholith must wait for the results of research to provide additional management 

 guidelines, and it may have to be managed for less than total resource potential if 

 adequate environmental safeguards are to be applied. 



Considerable attention is currently being directed to the Batholith area. It 

 contains valuable timber reserves as well as other resources which are important to the 

 regional and national economies. However, many of its steep slopes are highly erodible 

 and susceptible to landslides. More specifically, slopes are often greater than 60 

 percent and are commonly composed of highly fractured and weathered granite overlain 

 by thin layers of loose, cohesionless soils. Developmental activities, especially 

 roadbuilding , increase the occurrence of landslides and provide large exposed areas 

 from which sediment can readily be removed by normal erosional processes. Initial in- 

 creases in production of sediment have been measured and in some instances were more 

 than a thousandfold greater than natural rates from undisturbed terrain. 



The most serious consequence of this accelerated sedimentation is believed to be 

 destruction of aquatic habitat, especially of the spawning and rearing areas of anad- 

 romous fish (fig. 2). In addition, the silting of downstream reservoirs is an impor- 

 tant consideration, as is the visual impact of exposed cutbanks , fill slopes, debris 

 piles, and slide scars. 



This paper describes an investigation of slope failures in one small area of the 

 Batholith and the conclusions and recommendations derived therefrom. 



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