DIGITAL COMPILATION OF GEOLOGIC MAPS AND NEW STRUCTURAL AND STRATIGRAPHIC INTERPRETATIONS IN THE SOUTHERN SHENANDOAH VALLEY, VIRGINIA

Recent digital compilation of geologic mapping in the southern Shenandoah Valley was completed to support proper land development in the region. This project, supported by the USGS STATEMAP program, has provided an opportunity to review published and unpublished maps, conduct new mapping, and address regional geologic problems. Regional structures in the compilation area include the southern end of the Massanutten Synclinorium, the “Blue Ridge” fault, the Staunton-Pulaski fault system, and the Rockfish Valley fault. Extensive coalescing alluvial fans or pediments along the western flank of the Blue Ridge in this area conceal significant areas of bedrock. Challenges encountered during the compilation included contact location discrepancies (boundary faults), differing data types, non-uniform data distribution, differing stratigraphic resolution, and differing structural interpretations. In many instances, contact discrepancies were greatest where surficial deposits crossed map boundaries. For ease of editing, we have treated surficial geologic information as a separate entity from bedrock geologic information within our GIS framework. To resolve different structural interpretations, we combined original field map data with published data, data from new mapping, geophysical data, and any work in adjacent areas completed since the original map publication date. This has resulted in new interpretations of the “Blue Ridge” fault and the Staunton-Pulaski fault, and stratigraphic nomenclature changes within the Massanutten Synclinorium. Creation of the GIS files led to development of a new, standardized geologic font and symbol set now used in all DMR mapping projects. By putting geologic data into a GIS database, we can continuously update changes to stratigraphic nomenclature, structural interpretations, and contact locations.