The data on this CD consist of geographic information system (GIS) coverages and tabular data on the geology of Early Proterozoic and Archean rocks in part of the Early Proterozoic Penokean orogeny. The map emphasizes metasedimentary and metavolcanic rocks that were deposited along the southern margin of the Superior craton and were later deformed during continental collision at about 1850 Ma. The area includes the famous iron ranges of the south shore region of the Lake Superior district. Base maps, both as digital raster graphics (DRG) and digital line graphs (DLG) are also provided for the convenience of users. The map has been compiled from many individual studies, mostly by USGS researchers, completed during the past 50 years, including many detailed (1:24,000 scale) geologic maps. Data was compiled at 1:100,000 scale and preserves most of the details of source materials. This product is a preliminary release of the geologic map data bases during ongoing studies of the geology and metallogeny of the Penokean continental margin. Files are provided in three formats: Federal Spatial Data Transfer format (SDTS), Arc export format (.e00) files, and Arc coverages. All files can be accessed directly from the CD-ROM using either ARC/INFO 7.1.2 or later or Arc View 3.0 or later software. ESRI's Arc Explorer, a free GIS data viewer also provides display and querying capability for these files.

Multispectral remote sensing data acquired by the Landsat 8 Operational Land Imager (OLI) sensor were analyzed using a new, automated technique to generate a map of exposed mineral and vegetation groups in the western San Juan Mountains, Colorado and the Four Corners Region of the United States (Rockwell and others, 2021). Spectral index (e.g. band-ratios) results were combined into displayed mineral and vegetation groups using Boolean algebra. New analysis logic has been implemented to exploit the coastal aerosol band in Landsat 8 OLI data and identify concentrations of iron sulfate minerals. These results may indicate the presence of near-surface pyrite, which can be a potential non-point source of acid rock drainage. Map data, in ERDAS IMAGINE (.img) thematic raster format, represent pixel values with mineral and vegetation group classifications, and can be queried in most image processing and GIS software packages. Rockwell, B.W., Gnesda, W.R., and Hofstra, A.H., 2021, Improve ...