Digital geologic map of the Springdale 7.5' quadrangle, Nevada

The current map database incorporates geologic data from: (1) early preliminary geologic mapping (1963-1965) by P.P. Orkild (assisted by R.L. Christiansen); (2) more recent field mapping (1991-1995) of bedrock by S.A. Minor; (3) recent mapping (1994- 1995) of surficial deposits by WC Swadley; and (4) new detailed petrographic and geochemical data of Tertiary volcanic units of the southwest Nevada volcanic field obtained by R.G. Warren (Warren and others, 1997). Hand-drafted stable-base layers of the early mapping were scanned and vectorized and then edited using AutoCAD software. New geologic field data, which were mapped on 1:24,000-scale (bedrock) and 1:60,000- scale (surficial deposits) aerial photographs, were digitized directly from the photographs using a Kern PG-2 stereographic plotter interfaced with CADMAP digital capturing software. Also, clear-film positives of the topographic base map layers were scanned. All new digital files as well as the earlier AutoCAD map files were imported into the raster processing software LT4X for initial cleaning, editing and, in the case of scan files, vectorization. The new map data were also imported into AutoCAD for further editing. Geographic Resource Analysis Support System (GRASS), a public-domain GIS, was used to transform all of the new component map files to Universal Transverse Mercator projections, merge the files in the appropriate composite map-data layers, conduct final editing and modification of map elements, build and tag polygons, and assign attributes to map elements. Finally, the various data layers were converted to ArcINFO coverages and a plot file of the final geologic map was generated from them.