The ssfb_m1 digital map database, which is compiled from 1970's vintage sources, represents the general distribution and identity of geologic materials in the southern San Francisco Bay region, California, west of the Calaveras fault. It is not a geologic map, because it does not address the geologic structure or the stratigraphic organization of the map units in a systematic way. Instead, it is directed at the distribution and character of the geologic materials following the pattern of its progenitors, Wentworth and others (1985) and Ellen and Wentworth (in press). Consultation of these reports and the other compilation sources will aid in using the database.
The purpose of this digital map database is to provide a map of the distribution and character of the geologic materials following the pattern of its progenitors, Wentworth and others (1985) and Ellen and Wentworth (in press at the time of the release).
The full data set originally encompassed part or all of Sonoma, Marin, Napa, Solano, Contra Costa, Alameda, Santa Clara, San Mateo, and Santa Cruz counties. This data set has been clipped to Sonoma County
publication date
None
Mail Stop 977, USGS
345 Middlefield Rd
Compilation of the digital database depended on advice and assistance in the use of ALACARTE-ARC/INFO from T.T. Fitzgibbon and access to ARC/INFO made possible by the Menlo Park GIS Research Laboratory of the U.S. Geological Survey. E.J. Helley provided author linework of the surficial map for scanning. D.L. Knifong assigned UNIT values to the polygons for the Santa Cruz geologic map. D.S. Aitken of the GIS lab provided access to a digital version of the color boundaries for the geologic map of Santa Cruz County and scanned and vectorized the fault plates for that map and the hillside materials map and the several layers of the topographic base map. N.L. Hoskin provided access to working files of the color boundaries and polygon tags for the hillside materials map. S.D. Ellen and E.E. Brabb shared their geologic expertise about the region.
The database delineates map units that are identified by general age and lithology and by the map labels used in the compilation sources. Stratigraphic names are included for those units named in the sources as a further means of characterization.
Faults are distinguished in the database only as part of the physical character of the geologic materials and the database cannot be used to identify or delineate active faults in the region. Similarly, the database cannot be used to identify or delineate most landslides in the region.
Preliminary mapping of area
Preliminary mapping of the area
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.
Metadata imported.
Dataset copied.
Metadata imported.
Feature geometry.
ESRI
Materials category
OFR-93-0693
Landslide deposits
OFR-93-0693
Location of landslide deposit
Not a landslide deposit
Map unit symbols (parial definitions given)
OFR-93-0693
Body of water
Landslide deposit
Undifferentiated bedrock
Location of dam
Unmapped area
Unit label from compilation source
OFR-93-0693
All other counties in area
Santa Cruz County
AGE and LITH attributes combined
OFR-93-0693
soft, water-saturated mud, some silt
mud and silt
sand, gravel, silt, and mud
sand and gravel
mudstone and shale, some sandstone
sandstone, some mudstone
clay, silt, sand, gravel
sand, gravel, silt, and mud
landslide
agglomerate, breccia
mudstone, some sandstone
sandstone and mudstone
sandstone, some mudstone
tuff, tuffaceous sandstone, some sandstone, volcanic rock
felsic volcanic rocks
mafic volcanic rocks
mudstone and shale, some sandstone
porcelaneous and siliceous mudstone and shale
sandstone and mudstone or shale
sandstone, some mudstone or shale
limestone
diatomite, diatomaceous shale, some sandstone
tuff, tuffaceous sandstone, some sandstone, volcanic rock
welded tuff
agglomerate, breccia
felsic volcanic rocks
mafic volcanic rocks
silica-carbonate rock
mudstone and shale, some sandstone
sandstone and mudstone or shale
sandstone, some mudstone or shale
tuff, tuffaceous sandstone, some sandstone, volcanic rock
felsic volcanic rocks
mudstone and shale
sandstone and shale
sandstone and conglomerate, some shale
sheared sandstone and shale (melange)
metasandstone, some shale
metavolcanic rocks (greenstone)
chert
limestone
mafic volcanic rocks
felsic volcanic rocks
serpentinite
schist and marble
granitic rock
high-grade metamorphic rocks
Age of deposit
OFR-93-0693
Mesozoic
Quaternary
Quaternary-Tertiary
Lower Tertiary
Upper Tertiary
Holocene
Pleistocene
Age unknown
Numeric Ptype
OFR-93-0693
Holocene surficial deposits
Pleistocene and undivided Quaternary surficial deposits
soft sandstone, conglomerate, and clayey rock - largely Pliocene and Pleistocene deposits,
volcanic rock - largely Sonoma Volcanics, Miocene basalts, tuffs, and Franciscan greenstone.
firm sandstone and clayey rock - Tertiary sedimentary rocks, such as Briones and Neroly
siliceous rock - Mesozoic and Tertiary siliceous rocks, such as Franciscan chert and Claremont Shale
well-bedded, hard-firm sandstone and clayey rock - largely units of the Mesozoic Great
deformed hard sandstone and clayey rock - Franciscan sandstone.
mixed clayey sheared rock and masses of fractured hard rock - Franciscan melange and variably sheared Franciscan metagreenstone.
sheared serpentinite.
hard homogeneous rock - granitic rock, diabase, and unsheared ultramafic rock.
Geologic Unit
Feature geometry.
ESRI
Internal feature number.
ESRI
Lithology of map unit abbreviation
OFR-93-0693
mafic volcanic rocks
Felsic volcanic rocks
granitic rock
limestone
mud and silt
Mudstone and shale, some sandstone
Sheared sandstone and shale (melange)
Low-grade metasandstone and shale
Low-grade metavolcanic rocks (greenstone)
Sand, gravel, silt, and mud
Silica-carbonate rock
Schist
Porcellaneous or siliceous mudstone and shale; chert
Sandstone and mudstone or shale
Serpentinite
Sandstone and conglomerate, some mudstone or shale
Soft, water-saturated mud, some silt
Box 25286, Denver Federal Center
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Geologic units and structural features
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