Water Resources Division, U.S. Geological Survey 1974 <p>This map and accompanying table show Hydrologic Units that are basically hydrographic in nature. &nbsp;The Cataloging Units shown will supplant the Cataloging Units previously used by the U.S. Geological Survey in its Catalog of Information on Water Data (1966-72). &nbsp;The previous U.S. Geological Survey Catalog-Indexing System was by map number and letter, such as 49M. &nbsp;</p> application/pdf 10.3133/hu17 en U.S. Geological Survey Hydrologic Unit Map -- 1974, State of Kentucky reports