Fraticelli, L.A., Albers, J.P., Irwin, W.P., Blake, M.C. Jr., and Wentworth, C.M., 2012, Digital geologic map of the Redding 1¡x 2¡ quadrangle, Shasta, Tehama, Humboldt, and Trinity Counties, California: U.S. Geological Survey Open-File Report 2012-1228, scale 1:250,000 (http://pubs.usgs.gov/of/2012/1228/). This map database represents a digital rendition of Open-File Report 87-257, 1987, by L. A. Fraticelli, J. P. Albers, W. P. Irwin, and M. C. Blake Jr., with various improvements and additions. It was compiled by W.P. Irwin and C.M. Wentworth from a digital scan of the original Open-File map (included as the ArcInfo grid rd-mapscan) and shows the general distribution of bedrock and surficial deposits of the Redding 1x2-degree quadrangle at a regional (1:250,000) scale, as portrayed in the original map. It is intended to show the geologic frame-work and geologic history of the region. Geologic map units are identified by general age and lithology, largely following the stratigraphic nomenclature of the U.S. Geological Survey (the sources of some names used by Fraticelli and others (1987) remain unclear). Many uncertainties about lines and labels in the original map have been resolved, but many remain. The original open-file map was printed in black and white, with a screened base, and is quite detailed, making it very difficult to read. The raster scan of the original 1987 map used for the current digital compilation is included in the database (rd-mapscan) for comparison. It should be noted that cultural information in the base map is current as of 1976 (revision date of the base map). The southern half of the map area is covered by two geologic maps at 1:100,000, McLaughlin and others (2000) and Blake and others (1999). These, together with four 15-minute quadrangles by Irwin (2009, 2010a), Irwin and others (2010b, 2011) and Albers and others (1964), were consulted to help identify unlabelled polygons and resolve apparent geologic conflicts. Albers, J.P., Kinkel, A.R., Jr., Drake, A.A., and Irwin, W.P., 1964, Geology of the French Gulch quadrangle: U.S. Geological Survey Geologic Quadrangle Map GQ-336, map scale 1:62,500 Blake, M.C., Jr., Harwood, D.S., Helley, E.J., Irwin, W.P., Jayko, A.S., and Jones, D.L., 1999, U.S. Geological Survey Geologic Investigations Map I-2542, map scale 1:100,000 Fraticelli, L.A., Albers, J.P., Irwin, W.P., and Blake, M.C., Jr., 1987, Geologic map of the Redding 1x2 degree quadrangle, Shasta, Tehama, Humboldt and Trinity Counties, California: U.S. Geological Survey Open-File Report 87-257, map scale 1:250,000. Irwin, W.P., 2009, Geologic map of the Weaverville 15' quadrangle, Trinity County, California: U.S. Geological Survey Scientific Investigations Map 3095, scale 1:50,000 (http://pubs.usgs.gov/sim/3095/). Irwin, W.P., 2010a, Reconnaissance geologic map of the Hayfork 15' quadrangle, Trinity County, California: U.S. Geological Survey Scientific Investigations Map 3119, scale 1:50,000 (http://pubs.usgs.gov/sim/3119/). Irwin, W.P., 2010b, Reconnaissance geologic map of the Hyampom 15' quadrangle, Trinity County, California: U.S. Geological Survey Scientific Investigations Map 3129, scale 1:50,000 (http://pubs.usgs.gov/sim/3129/). Irwin, W.P., Yule, J.D., Court, B.L., Snoke, A.W., Stern, L.A., and Copeland, W.B., 2011, Reconnaissance Geologic Map of the Dubakella Mountain 15' Quadrangle, Trinity, Shasta, and Tehama Counties, California: U.S. Geological Survey Scientific Investigations Map 3149, scale 1:50,000 (http://pubs.usgs.gov/sim/3149/). McLaughlin, R.J., Ellen, S.D., Blake, M.C., Jr., Jayko, A.S., Irwin, W.P., Aalto, K.R., Carver, G.A., and Clarke, S.H., Jr., 2000, Geology of the Cape Mendocino, Eureka, Garberville, and southwestern part of the Hayfork 30- x 60-minute quadrangles and adjacent offshore area, northern California: U.S. Geological Survey Miscellaneous Field Studies Map MF-2336, map scale 1:100,000. NOTE: The projection for the Arc export file, shape files, and Arc grids is Transverse Mercator (see below). The projection datum for these files and the map graphic is NAD27 (NOT 83). Projection TRANSVERSE Units METERS Spheroid CLARKE1866 Parameters 1.00000000 /* scale factor at central meridian -123 0 0.000 /* longitude of central meridian 0 0 0.000 /* latitude of origin 0.00000 /* false easting (meters) 0.00000 /* false northing (meters) The report consists of the following parts: 1. This README - of2012-1228_readme.txt 2. Version History - list showing status of any revisions to the report. Accessed by clicking on the "First posted..." or "Last modified..." link on the webpage. 3. Pamphlet - of2012-1228_pamphlet.pdf: A modification of the original pamphlet that accompanied OFR 87-257, as a PDF file. Includes a description of the digital compilation of the map, a description of map units, and a map and list of sources used in the original 1987 compilation. 4. Metadata file - of2012-1228_metadata.txt: text file of FGDC-compliant metadata documenting the vector geologic database. 5. Map Graphic - of2012-1228_map.pdf - geologic map and explanation as a PDF file. 6. GIS database - of12-1228-arcpkg.zip: a compressed directory containing the exported ArcInfo coverage, equivalent shape files, and accompanying metadata file. of12-1228-geo.e00 - ArcInfo Export file of the geologic GIS layer, containing contacts, faults, and unit polygons. of12-1228-geo-shape Compressed directory containing ESRI line and polygon shape files prepared from the coverage of12-1228-geo. of12_1228_ln.dbf prj sbn sbx shp shx shp.xml of12_1228_py.dbf prj sbn sbx shp shx shp.xml of12-1228-metadata.txt - text file of FGDC-compliant metadata documenting the GIS layer. 7. of12-1228-base.zip - Compressed directory containing base image and text description. rd-base - ArcInfo grid of the Redding, California, 1¡ x 2¡ topographic map, in Transverse Mercator NAD27 projection. of12-1228-basenotes.txt - text description of the grid values for the different map components. 8. of12-1228-mapscan.zip Compressed directory containing image of the original, black-and-white geologic map (Fraticelli and others, 1987) rd-source - ArcInfo grid representing a gray-scale raster scan of the original. black-and-white open-file map (Fraticelli and others, 1987), in Transverse Mercator NAD27 projection.