1978. United States. Soil Conservation Service. Base source: USGS 1:100,000 county base map dated in 1976; interpretations derived from soil map constructed 1960.; "Projection and 10,000-metre gr... Dept. of Agriculture, Soil Conservation Service (Washington.).
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1979. United States. Soil Conservation Service. Base compiled in 1976 from USGS 1:24,000-scale topographic maps dated 1965-68; planimetry revised from aerial photographs taken 1974.; "Projection ... Dept. of Agriculture, Soil Conservation Service (Washington.).