NEW AND UPDATED GEOLOGIC MAPPING IN THE CONGAREE RIVER VALLEY, CENTRAL SOUTH CAROLINA

Geologic mapping by South Carolina Geological Survey (SCGS) is evolving to reflect technological advances as well as demands of sophisticated map customers. Our goal is to provide digital map products in a GIS format. Several techniques are illustrated by our recent mapping in and around Congaree National Park, which was part of a 2-year, 10-quadrangle project to produce geologic information for the National Park Service.

The map development process began with digital capture of field, archival, and existing digital datasets to establish a geodatabase with various layers (point, line, area). Original field, outcrop, and subsurface (power-auger) data provided the bulk of the original point layer. More than 20,000 feet of variable-quality subsurface data also was provided through public records and geotechnical reports. The geologist interpolated map lines between points by constantly referencing a variety of supplemental digital datasets including DOQQs, LIDAR, DRGs, DEMs, NWI, SSURGO, and regional aeromagnetic data. Older 1:24,000 SCGS maps in adjacent areas also were digitized for reference. Topologic rules were applied to map lines prior to constructing polygons. Cross sections were developed by digitally extracting intersection points of polygon boundaries across a line of section, hand drafting the section, and then digitizing for inclusion on the map layout. Final map layout was done with graphic and cartographic software, and the resulting digital map products of the Congaree River valley include 5 completely new 1:24,000 geologic maps and a 1:12,000 flood-plain map. The geologic maps delineate 14 Plio-Pleistocene fluvial terraces. Delineation of numerous subtle terraces, alluvial fans, and Carolina Bays would not have been possible without the integrated approach.