Hydrologic Unit Map -- 1974, State of Pennsylvania

This map and accompanying table show Hydrologic Units that are basically hydrographic in nature.  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).  The previous U.S. Geological Survey Catalog-Indexing System was by map number and letter, such as 49M.