THE LAKE TAHOE GEOLOGIC INFORMATION SYSTEM: A NATIONAL GEOLOGIC MAP DATABASE PROJECT PILOT

As a pilot within the National Geologic Map Database (NGMDB) project, fourteen existing geologic maps of the Lake Tahoe region at several scales—roughly half of a 1° sheet, straddling the states of California and Nevada—were digitized as GIS coverages and attributed according to the original North American Data Model (NADM) v4.3. Subsequently, these maps were ingested into an ESRI geodatabase, embedding both geometry and attributes, from which a new map is being compiled at a nominal 1:24K scale in the current NADM Norton v1.0 specification. Both data model formats are supported and editable concurrently in ESRI ArcGIS v8.3, with additional capability provided by the GEM [Geologic Editor Module] tool developed under auspices of NGMDB. The historical maps could only be attributed from their accompanying legends and narratives; the new map incorporates additional detail from recent fieldwork, augmented by research and teaching. Of particular note is an expert system, GeoGen [Geologic Generalization Expert System], built atop the encoded map information, which automates production of selected derivative maps and facilitates interpretation of environmental parameters such as slope stability, erosion potential, and macro-nutrient availability. This poster describes the regional map suite at Lake Tahoe and the geologic information system built from it, and also demonstrates prototypes of the GEM and GeoGen software tools.