Open-File Report 2006-1259

Published 2006
Online Only

Climate, Vegetation, Soils, and Topography

The Snow Camp-Saxapahaw study area is within the humid subtropical climatic zone and receives 40 to 60 inches (in) (100 to 150 centimeters (cm)) of annual precipitation. The area has relatively flat to gently rolling relief, but there are a few hills of more resistant rocks. The most prominent of these are the Cane Creek Mountains (fig. 2, fig. 3, fig. 4A, and fig. 5, sectors A–C and E) and the Mine Ridge near the Snow Camp pyrophyllite mine (sector J) that have altitudes of 1,033 (feet) ft (315 meters (m)) and 750 ft (229 m), respectively. Most of the area is drained by the Haw River that crosses its northeastern corner, but tributaries of Rocky River, to the southwest, drain the southwestern part. The land is used mainly for field crops, woodland, and pasture. A few planted forests in the area consist of a single species of pine.

Areas underlain by felsic flow rocks and siliceous hypabyssal intrusions, or highly siliceous altered rocks have generally greater topographic relief, more outcrops, and more forest cover than adjacent areas of tuffs, volcaniclastic rocks, and mafic bedrock. The dominant tree species is chestnut oak, Quercus prinus L., on most felsic and siliceous rock sites. Weathering of most other rocks resulted generally in low relief. These areas are partly forest covered and partly cultivated. Plutonic rocks are sparse in the lowlands and streambeds, therefore the relations of these rocks were especially difficult to determine. Where rock exposures are sparse, the distinction between fine-grained porphyritic intrusive rocks and porphyritic flows and crystal tuffs were difficult to make; consequently, the abundance of small subvolcanic masses may have been substantially underestimated.

Most of the soils in the area are residual, but alluvial soils are present in small areas on stream flood plains. Some residual soils are clearly related to bedrock types and, therefore, were used as an aid in geologic mapping. The U.S. Department of Agriculture (USDA) Soil Conservation Service soils map of Alamance County (Kaster, 1960) was used extensively during field mapping, and USDA field personnel concurrently mapping the soils of Chatham County supplied copies of their field work sheets for use in our geologic studies on the northern edge of that county. Except on rocky ridges, residual soil is generally underlain by saprolite, leached of many of the original rock-forming minerals, but retaining much of the original rock texture. Depending on the depth to the water table at the particular site, the saprolite may be as much as 80 ft (25 m) thick.

At the time of our field mapping, extensive lithologic and stratigraphic studies had been carried out in only a few specific areas of the Carolina slate belt in North Carolina (see Conley, 1962; Stromquist and others, 1971; Smeds, 1972; Lyday, 1974; Hadley, 1974; Hauck, 1977; Wilkinson, 1978; Seiders, 1981; Carpenter, 1982; Harris, 1982; Sexauer, 1983; Chiulli, 1987; Eligman, 1987; and Goldsmith and others, 1988). Major problems remain in the interpretation of structural geology and stratigraphy.

 
 

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