"March 1993 1007595." Includes location map and source materials note. Available also through the Library of Congress Web site as a raster image.
United States. Soil Conservation Service; National Cartography And Geographic Information Systems Center (U.S.)
<a rel="nofollow" class="external free" href="https://www.loc.gov/item/93682959/">https://www.loc.gov/item/93682959/</a>