1980. Geological Survey (U.S.). This polygon shapefile contains the 1980 state and county boundaries of the United States, Puerto Rico, and the U.S. Virgin Islands. The map layer ... Geological Survey (U.S.).
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1980. United States. Soil Conservation Service. Base source: USGS 1:100,000 county base map dated 1978; interpretations derived from soil map constructed 1972.; "Projection and 10,000-metre grid ... Dept. of Agriculture, Soil Conservation Service (Washington.).
1980. United States. Soil Conservation Service. Base source: USGS 1:100,000 county base dated 1979; interpretations derived from soil map constructed 1979.; "Projection and 10,000-metre grid tick... Dept. of Agriculture, Soil Conservation Service (Washington.).
1980. United States. Soil Conservation Service. Base source: USGS 1:100,000 county base dated 1978; interpretations derived from soil map constructed 1956.; "Projection and 10,000-metre grid tick... Dept. of Agriculture, Soil Conservation Service (Washington.).