drainage are expected to increase as a result of wildfire and may cause an 

 increase in channel instability, as well as increased road erosion. 



3.2.1.5 Geology and Soils 



Geology 



Refer to Geology Map 2 (Appendix B: Figure B-2) for project area geology. 



The project area is located on moderate to steep slopes with no especially 

 unique or unusual geological features present in the proposed project area. 

 The dirty Ike watershed is of the Missoula group Belt Series formation. This is 

 a sedimentary rock type from the Precambrian era consisting of metased 

 argillite and sandy or quartzitic argillite. 



Geology in the upper portion of the Ashby Creek watershed is a composition 

 of Cambrium (Cu), undifferentiated sedimentary rock from the Paleozoic 

 period and Boulder Batholith (TKb) and other broadly related intrusive rocks 

 from the Cenzoic-Mesozoic period. 



Cambrium rock is layered sedimentary shale, limestone and quartzite. The 

 Boulder Batholith is large masses of intrusive igneous rock (granite). The 

 Boulder Batholith consists of soils that are weak and brittle when weathered 

 and highly susceptible to accelerated rates of erosion. 



The Wallace Creek drainage is a combination of Boulder Batholith (TKb) 

 intrusive rock, Missoula Belt Series (pCm) rock and a small section of 

 Cambrian, undifferentiated (Cu) sedimentary. 



Soils 



Refer to Soils Map 3 (Appendix B: Figure B-3) for project area soils. 



Soils in the project area are a combination of Evaro Gravelly Loam 8-30% 

 slopes, Evaro Gravelly Loam 30-60% slopes, Winkler Gravelly Loam 30-60% 

 slopes Winkler Gravelly Loam, Cool 30-60%slopes and Tevis Gravelly Loam 

 8-30%. 



Evaro Gravelly Loams have a colluvium parent material derived from argillite 

 and quartzite, are somewhat excessively drained and a mean annual 

 precipitation of 20-30 inches. These soils are very deep (>60 inches) and have 

 an available water holding capacity of 3.7 inches. These soils, which range in 

 elevation from 4,500 to 6,000 feet, have a high content of volcanic ash in the 

 surface layer. These soils have a topsoil layer of gravelly loam 0-4 inches and 

 a subsoil layer of > 60 inches. 



Winkler Gravelly Loams are very deep, somewhat excessively drained; have a 

 colluvium parent material derived from argillite and quartzite and a mean 

 annual precipitation of 17-30 inches. They have a gravelly loam surface layer 



Dirty Ike Salvage Environmental Assessment 3-10 



