Each of the units that make up the District is a discrete, 

 prominent escarpment on the unglaciated high plains landscape, with 

 distinct surface geology and vegetation. They include the highest 

 points in the counties and contain a range of environmental and 

 biological features in unigue forms and combinations. 



The study area escarpments are capped by relatively resistant 

 Tertiary sedimentary deposits, including (from oldest to youngest) : 

 the Arikaree Formation of gray sandstone with layers of 

 concretions; the Tongue River member of the Fort Union Formation 

 with clay, shale, siltstone and sandstone; and the White River 

 Group formations with light colored (calcareous) clay and local 

 beds of sandstones (Ross et al . 1955). There are small outcrops of 

 the older Hell Creek Formation that flank the southern units in 

 Harding County (Slim Buttes, Short Pine Hills) . Some of the most 

 extensive calcareous outcrops of the White River Group in the 

 three-state area are in the Sioux District of Custer National 

 Forest, including the Slim Buttes, Chalk Butte, and restricted 

 areas of the Long Pines, South Cave Hills, and lands mainly north 

 of U.S. Forest Service boundaries in the East Short Pines. Each of 

 the escarpments are erosional features that were more or less all 

 part of a broad plain during the late Miocene time (Bluemle 1991) . 

 They were created during the late Pliocene time 3-5 million years 

 ago during a major cycle of widespread erosion, and persist above 

 surrounding Cretaceous tablelands. 



Soils are mapped in detail for Harding County (Johnson 1988) , and 

 the Carter County soil survey is in progress. The upper levels of 

 soil taxonomy have been mapped for Carter County in a preliminary 

 manner by Montagne et al. (1982) ; under which the Sioux District 

 Units are made up of primarily of Ustochrepts, Ustorthents, and 

 Haploborolls (i.e., dry, northern prairie soils under varying 

 degrees of soil development) . Similarly, the Slim Buttes are 

 primarily covered by the Reva-Rockoa association of well-drained, 

 shallow to deep, moderately sloping to very steep calcareous soils 

 of gravelly and loamy texture. The Cave Hills are primarily 

 covered by the Cohagen-Rock outcrop association of well-drained, 

 shallow, moderately sloping to very steep loamy and sandy loam 

 texture. The Short Pine Hills are primarily covered by the 

 Cohagen-Rock outcrop association of well-drained, shallow, 

 moderately sloping to very steep loamy soils. 



The study area has a continental semi-arid climate characterized by 

 temperature extremes, ranging almost 150 degrees F annually, and 

 freguently up to 40 degrees daily; accentuated by windy conditions 

 (Visher 1914) . In general, the study unit buttes are more exposed 

 and with a wider range of microclimates compared to the surrounding 

 plains. The growing season length and conditions are highly 

 variable. Average annual precipitation is 14.7 inches (37.4 cm) in 

 Harding Co. (Johnson 1988), but two out of ten years typically have 

 severe drought conditions with less than 9 in (22.86 cm) during the 

 growing season. About 75% of the annual precipitation falls during 



