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Physiographic Regions & Description

 

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Chapter 2 - Study Area

Physiographic Regions & Description   |   Population   |   Agriculture Industry 

Physiographic Regions & Description

Carroll County is located within the Ozark Plateau Province, a physiographic region covering 40,000 square miles west of the Mississippi River (Fenneman, 1938). The Salem Plateau, the Springfield Plateau, and the Boston Mountains constitute the major divisions of the Ozark Plateau Province within the political bounds of Carroll County. (Figure 2.2) This region of northwest Arkansas is also referred to as the Ozark Highlands Eco-Region (State of Arkansas, Dept. of Pollution Control & Ecology, 1987).

Figure 2.2

 

The Salem Plateau is the northernmost division of the Ozark Plateau Province in Carroll County. The Salem Plateau covers much of the north central portion of Carroll County. Its surface is lower than the surface elevation of both the Springfield Plateau and the Boston Mountains. This plateau has been down-cut by the White River and its tributaries. The plateau’s topography within Carroll County varies from roughly 900 to 1250 feet above sea level, although the tops of hills and ridges stand nearly at the same general level of elevation. The Surface Bedrock is of Ordovician Age being largely dolomite and limestone. The majority of the hills are low and well rounded. The Eureka Spring escarpment separates the Salem Plateau from the Springfield Plateau. The escarpment extends some 250 to 450 feet above the Salem Plateau, but north of Green Forest it extends only 100 feet above this surface level (Purdue & Miser, 1916).

The Springfield Plateau ranges between roughly 1,000 to 1,750 feet in elevation in Carroll County. It is a dissected structural plain whose surface at most places conforms to that of the underlying Boone Limestone with cherty beds that have been preserved (Purdue & Miser, 1916). The surface of the Springfield Plateau is rather rough, particularly near its northern border, where streams are cutting back into the Eureka Springs escarpment. In a few areas, however, the surface of the plateau is only gently undulating where relief rarely is more than 100 feet. This area in eastern Carroll County comprises the better farmland of the plateau. The Springfield Plateau is separated from the Boston Mountains by the Boston Mountain escarpment. However, outliers of the Boston Mountains extend onto the surface of the Springfield Plateau. A few valleys of 500 to 1,250 feet deep warrant the application of the term mountainous to this highland region (Croneis, 1930).

The northernmost boundary of the Boston Mountains region is located in the southeast portion of Carroll County. The mountains extend from 300 to 700 feet above the surface of the Springfield Plateau at elevations ranging from 1,700 to 2,200 feet above sea level. The surface tops of this physiographic division form an eroded tableland having approximately the same surface level. The Boston Mountains are the erosional remnants of the dissected Boston Mountain Plateau. The caprock of the formation is largely sandstone and shale. Valleys range from 500 to 1,400 feet below the upland surface and can be as long as 15 to 20 miles (Croneis, 1930).

Carroll County’s surface formations consist of limestone, dolomite, sandstone, shale, and chert. These are all sedimentary rocks, which range in age from Lower Ordovician to Pennsylvanian (Croneis, 1930). (Figure 2.3)

Figure 2.3

 

The soils in Carroll County occur in an orderly pattern that is relative to the geology, the landforms, relief, climate, and the natural vegetation of the area. The soils in Carroll County are typically classified as ultisols, meaning they are generally acidic and relatively infertile. There are twenty-two recognized soil series located within Carroll County. Each soil unit consists of one or more major soils and some minor soils. The map units are identified and named according to the taxonomic classification of the dominant soil or soils (Fowlkes, et. al., 1984). Map Foldout 2.2 presents the classified soil mapping units located within Carroll County.

Carroll County is also located with the upper portion of the White River Watershed (U.S. Army Corps of Engineers, 1988). The river flows across the northwest region of the county and is impounded in the county by Beaver Dam creating the Beaver Lake Reservoir located in Washington, Benton, and Carroll Counties. The prime tributaries of the White River in the northwestern section of Carroll County are North Clifty Creek, Big Clifty Creek, and Leatherwood Creek. The Kings River, which has its headwaters located in Madison County in the Boston Mountains, flows through Carroll County and enters Table Rock Reservoir on the White River near the Barry and Stone County boundary in Missouri. Principal tributaries to the Kings River are Osage Creek, Piney Creek, Dry Fork, and Keel’s Creek. Long Creek receives the drainage of the extreme eastern section of the county. It enters the White River at Table Rock Reservoir. Primary tributaries to Long Creek are Yocum Creek and Dry Creek. These streams are classified as perennial streams. (Map Foldout 2.3) Springs, which are common in Carroll County, contribute substantially to stream flow during the summer and fall (State of Arkansas, Dept. of Pollution Control & Ecology, 1987).

Map Foldout 2.2 (Click to view full size)

Map Foldout 2.3 (Click to view full size)

 

The natural vegetation of this region of northwest Arkansas is characterized by upland hardwood forests with shortleaf pine and cedar glades. Portions of the Salem and Springfield Plateaus also contain upland prairies which are now predominantly utilized as improved pasture (State of Arkansas, Dept. of Pollution Control & Ecology, 1987). A note of further reference is Foti et al (1994), who present a hierarchical classification system on a species level of existing natural vegetation of Arkansas with respect to landforms and regions. This system was developed for utilization in the Arkansas Gap Analysis Project and it has been suggested by Foti et al that this natural vegetation classification system form the basis for future vegetation analyses and research within Arkansas.