The soils are mostly residual and poorly developed, often little altered from the underlying 

 sedimentary formations, mostly shales and claystones. In areas with badland and breakland 

 topography, erosion greatly outpaces soil development. Alluvial soils are found along many 

 tributaries on BLM land, but extensive alluvial plains along the major drainages are mostly on 

 private land. Carter County BLM lands with sandy soils are relatively uncommon. These are found 

 peripheral to the Custer National Forest units and isolated in the Humbolt Hills in northeast, in the 

 Powder River headlands in the northwest and southwest, near Albion in the extreme southeast, and 

 in the Finger Buttes area also in the southeastern quarter of the county. 



A schematic way of aggregating environmental factors to present an overview of geology, 

 landforms, and soils is depicted in maps of ecological regions (ecoregions). The study area is within 

 a segment of the Great Plains that has been referred to as the Unglaciated Missouri Plateau section 

 (Fenneman 1931). A more current classification places the county wholly within Bailey's Great 

 Plains-Palouse Dry Steppe (map label 331, Nesser et al. 1997), with two section divisions and two 

 subsection divisions (see Figures 2 and 4 for these superimposed ecoregional boundaries). The 

 Northwestern Great Plains Section (33 IF) includes the great majority of the county's land area, 

 followed by the Powder River Basin Section (33 IG). The former is provisionally divided into 

 Subsections on the basis of geological formations and degree of relief; the southern 1/3 of the county 

 is Shale Scablands (331Fb), and the northern 2/3 is Pierre Shale Plains (331Fc). The latter is 

 provisionally divided into the Powder River Basin /Breaks/Scoria Hills and the Montana 

 Sedimentary Plains Subsections. These ecological region boundaries are discussed as they relate to 

 vegetation on the following page. 



Climate 



The climate of Carter County is semi-arid (precipitation ranging fi-om 10 to 15 inches) and temperate 

 continental (4-7 months > 10° C, coldest month < 0° C). The bulk of precipitation comes in late 

 spring-early summer, peaking in June. Rainfall during the summer is mainly from cloudbursts and 

 thunderstorms, typically very light but sometimes accompanied by lightening, heavy hail, and 

 occasionally, flash flooding. The growing season conditions are highly variable within and between 

 years. It has been noted in adjoining Harding County that large diurnal temperature changes are 

 frequent and accentuated by windy conditions (Visher 1914). Severe drought conditions are typical 

 in two out often years (Johnson 1988). The growing season conditions are also highly variable with 

 distance across the same region. In 1994, net January-June precipitation at Ekalaka (8.66 inches) was 

 almost twice that of nearby Camp Crook (4.43 inches; from The Ekalaka Eagle of 8 July 1994). This 

 climatic variation in turn is a strong influence on, in a complex fashion, the two major historic 

 disturbance regimes of the prairie, ungulate grazing and wildfire. 



All of this variation over time and space is averaged out in calculating totals and means. A 

 comparison of mean climate values at two different places in the county shows very similar values 

 and patterns. We include two diagrams ("Walter-type"; Figure 3) of the climates in two towns at 

 opposite ends of the county, portraying a consistent climatic pattern that is taken to represent the 

 plains of Carter County in general. The period and magnitude of the growing season's "relative 

 drought" is the area in Figure 3 delineated by the temperature curve's rise above the precipitation 



