General distribution of geologic materials in the southern San Francisco Bay region, California: A digital map database

The digital map was compiled on a 1:125,000 topographic base* (scanned and vectorized version of sheet 3, U.S. Geological Survey, 1970) from three regional compilations of 1970's data. Two of the sources were compiled in the 1970's on the 1:125,000 base and address the surficial deposits (flatland deposits, Helley and others, 1979) and the bedrock (hillside materials, Ellen and Wentworth, in press) of the 9-county San Francisco Bay region. (The San Mateo County part of the hillside materials map is based, in turn, on Wentworth and others, 1985.) The geologic map of Santa Cruz County (Brabb, 1989), also based largely on 1970's and older data, was compiled on the same base enlarged to a scale of 1:62,500. Inked or scribed linework for these sources was scanned (400 or more lines per inch), converted from raster to vector format, imported into ARC/INFO (version 4), and hand edited and combined into a single coherent map. The original material used to digitize the surficial linework was author manuscript (ink on mylar) and for the hillside materials and Santa Cruz County geologic maps was print publication files that had previously been prepared for color separation by scribing and scanning, together with scribed fault plates that were separately scanned and vectorized. The faults and color boundaries were combined interactively by hand for each source separately using ALACARTE (the color boundaries were tagged as contacts or replaced by faults, as appropriate). The fault plate for Santa Cruz County required a slight xy shift and rotation in the computer to produce a reasonable fit with the color boundaries.