Preliminary geologic map of the San Francisco South 7.5' quadrangle and part of the Hunters Point 7.5' quadrangle, San Francisco Bay area, California: A digital database

The geologic map information was digitized from stable originals of the geologic map at 1:20,000 scale. A mylar copy of the earlier map (Bonilla 1965) was scanned using a Altek monochrome scanner with a resolution of 800 dots per inch. The scanned images were vectorized and transformed from scanner coordinates to projection coordinates with digital tics placed by hand at quadrangle corners. The scanned lines were edited interactively by hand using ALACARTE, color boundaries were tagged as appropriate, and scanning artifacts visible at 1:24,000 were corrected. Base Map layers were prepared from scale-stable printing negatives of the U.S. Geological Survey San Francisco South (1980 photorevision), and Hunters Point (1980 photorevision) 1:24,000 topographic maps, which have a 25 foot contour interval. These base map layers are digital images but no information other than location is attached to the lines. The base maps are provided for reference only.