"May 1987." Includes note and location map. "1000612." Available also through the Library of Congress Web site as a raster image.
United States. Soil Conservation Service; National Cartographic Center (U.S.)
1987
<a rel="nofollow" class="external free" href="https://www.loc.gov/item/88690963/">https://www.loc.gov/item/88690963/</a>