Hydologic Unit Code Boundaries, 4th Level - Green River Basin (2001)

The Geographic Information Retrieval and Analysis System (GIRAS) was developed in the mid 70s to put into digital form a number of data layers which were of interest to the USGS. One of these data layers was the Hydrologic Units. The map is based on the Hydrologic Unit Maps published by the U.S. Geological Survey Office of Water Data Coordination, together with the list descriptions and name of region, subregion, accounting units, and cataloging unit. The hydrologic units are encoded with an eight- digit number that indicates the hydrologic region (first two digits), hydrologic subregion (second two digits), accounting unit (third two digits), and cataloging unit (fourth two digits). The data produced by GIRAS was originally collected at a scale of 1:250,000. This data set is a modification for Wyoming of the original United States HUC data produced by the USGS. The primary modifications made in this data set by the Wyoming Water Resources Center include 1) removal of hydrologic units that do not drain witi Wyoming and 2) modification of the hydrologic unit boundaries to better encompass streams and lakes represented in the 1:100,000 scale Digital Line Graph (DLG) of surficial hydrography. The HUC boundaries have not been "clipped" to the Wyoming border, in order to maintain the natural boundaries of the units. This metadata has also been altered from original USGS metadata to be more specific for Wyoming.