and is divided into three members, tlie Tullock, Lebo and Tongue River. The 

 Tongue River member contains the coal beds of the proposed Circle West strip 

 mine. 



During Pleistoceno continental glaciation, glaciers deposited till through- 

 out the northern half of the study area. Erosion has removed most of the till 

 along all the main streams and rivers and little remains south of the Missouri 

 River. 



Alluvium, consisting of silt, sand, and gravel, underl ies the bottom lands 

 of most of the major streams and rivers in the study area. Saline soils, which 

 result from a combination of poor subsurface drainage and a nearby source of 

 salts, are widespread on poorly drained alluvial terraces, especially in the 

 southern half of the study area. Salts are derived from the leaching of shale 

 beds in the Tongue River member of the Fort Union formation and from the Bear- 

 paw Shale. Other formations also have saline shales which may locally contri- 

 bute to salinity buildup. Leaching of salts may be accelerated where permeable 

 zones have been formed by the burning of coal beds within saline shale sequences. 



Badlands topography is common in areas underlain by the Fox Hills, Hell 

 Creek and Tullock units, primarily in the western third of the area. Silt 

 deposits, probably wind-blown loess (Colliver and Knechtel 1939), mantle many 

 parts of the area and may have influenced the present topography. 



Several major kinds of soils are found in the study area. These are Erti- 

 sols and Aridisols (Lithosols and Brown soils), e.g. Bainville silt loam; 

 Mollisols (Chestnut and Chernozem soils), e.g. Bearpaw clay loam, Sprole loam, 

 Vida loam; Ertisols and bedrock outcrops (badlands); Aridisols and some ar- 

 gids and natrargids (glaciated Brown and Solodized-Solenetz soils), e.g. 

 Phillips loam, Scobey clay loam, Thony loam; and Fluvents (allivial soils), 

 e.g. Bowdoin clay, Lohmiller clay loam (after Southard 1973). 



Elevations range from 604 m (1980 feet) where the Missouri River leaves 

 the study area to a high of 878 m (2882 feet) near Weldon Junction. Drainage 

 heads near the center of the study area are often characterized by steep dendri- 

 tic coulees which may cut 10 m (33 feet) or more beneath the plane of the sur- 

 rounding uplands. 



VEGETATION AND HABITAT CATEGORIES 



The Importance of Vegetation 



Wildlife populations cannot exist without suitable habitat; hence, know- 

 ledge of existing habitats and their quality and distribution is fundamental to 

 wildlife inventory and impact analysis. Vegetation, topography, slope, soils, 

 and local climate are among the most important components of wildlife habitat, 

 and can often be correlated with the diversity, productivity, biomass, and dis- 

 tribution of terrestrial animals. Such correlation was a primary objective of 

 this study. 



Vegetation was identified as the single most important component of wild- 

 life habitat in the study area, as it not only reflects such site factors as 



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