Geologic Map and Map Database of Northeastern San Francisco Bay Region, California Most of Solano County and Parts of Napa, Marin, Contra Costa, San Joaquin, Sacramento, Yolo, and Sonoma Counties By R.W. Graymer, D.L. Jones, and E.E. Brabb Pamphlet to accompany MISCELLANEOUS FIELD STUDIES MAP MF-2403 Version 1.0 2002 U.S. Department of the Interior U.S. Geological Survey Contents Geologic explanation and acknowledgements 1 Introduction 1 Stratigraphy 2 Mesozoic terrane complexes 2 Tertiary Stratigraphy 2 Structure 3 Description of Map Units 4 Acknowledgements 14 Digital publication and database description 15 Introduction 15 For those who don’t use digital geologic map databases 15 MF-2403 Digital Contents 15 PostScript plotfile package 16 PDF plotfile package 16 Digital database package 16 Tar files 17 PostScript plot files 18 PDF plot files 18 Obtaining the Digital Database and Plotfile Packages 18 To obtain tar files of database or plotfile packages from the USGS web pages 19 To obtain tar files of database or plotfile packages by ftp 19 Obtaining plots from a commercial vendor 19 Obtaining plots from USGS Map On Demand Services 19 Revisions and version numbers 19 Digital database format 19 Converting ARC export files 20 Digital compilation 20 Base maps 20 Faults and landslides 20 Spatial resolution 20 Database specifics 20 Lines 21 Areas 22 Points 24 References Cited 25 ii Geologic Explanation and Acknowledgements Introduction The map area includes all but the eastern edge of Solano County, eastern Napa County, and surrounding This report contains a new geologic map at 1:100,000 small parts of Marin, Sonoma, Yolo, Sacramento, San scale, a set of geologic map databases (Arc-Info coverages) Joaquin, and Contra Costa Counties. This area includes containing information at a resolution associated with the Sacramento-San Joaquin River delta in the southeast, 1:62,500 scale, and a new description of geologic map flat Central Valley in the east, rugged mountains of units and structural relationships in the mapped area. The modest height (mostly less than 800 meters) in the map database represents the integration of previously northwest and western parts, and rolling hills surrounding published reports and new geologic mapping and field San Pablo and Suisun Bays in the southwestern and checking by the authors (see Sources of Data index map southern parts. The northern and central mountains and on the map sheet or, for digital-data users, the Arc-Info delta areas are largely uninhabited, but the eastern valley coverage nesf-so and the textfile nesf-so.txt). The lands and the areas surrounding the bays are undergoing descriptive text (below) contains new ideas about the rapid development. geologic structures in the area, including the active San The map in this report is modified from and Andreas fault system, as well as the geologic units and supercedes U.S. Geological Survey Miscellaneous Field their relations. Studies Map MF-484 (Sims and others, 1973). Two Together, the map (or map database) and unit factors led to the decision to remap the area. First, there descriptions in this report describe the composition, has been almost 30 years of new geologic information distribution, and orientation of geologic materials and gathered for the map area. Second, tectonic theories for structures within the study area at regional scale. the California Coast Ranges have changed since the Regional geologic information (between about 1:50,000 publication of the earlier map, and the new tectonic and 1:100,000 scale) is important for analysis of models have a strong influence on the depiction of earthquake shaking, liquifaction susceptibility, landslide through-going active faults, volcanic fields, folds, and susceptibility, engineering materials properties, mineral other mapped features. Changes in the map include the resources and hazards, and groundwater resources and following: hazards. It is also vital for answering questions about the geologic history and development of the California Coast 1. An updated depiction of the active Concord-Green Ranges. Valley and Rodgers Creek Fault Zones. The information, however, is not sufficiently 2. New Quaternary surficial deposits mapping throughout detailed for site-specific investigations. Those seeking the map. information for specific sites should consult the detailed 3. Mapping of areas in Sacramento and Yolo Counties work of the earthquake-hazards maps produced by the left blank on the earlier map. California Division of Mines and Geology or contact a 4. Extensive revisions based on new mapping in Sears licensed geologist or engineering geologist. Point, Cordelia, Benicia, Cuttings Wharf, Fairfield The digital nature of the geologic map South, Denverton, and Lake Berryessa quadrangles. information is important for three reasons. First, the 5. Reinterpretation of the Early Cretaceous section in the geologic map data can be digitally combined with other northwestern part of the map. map datasets (topography, groundwater information, 6. Inclusion of major subsurface faults north and east of landslide distribution) for rapid and complex analysis of Suisun Bay. geologic resources and hazards. Second, digital maps are much more easily updated than traditional printed maps. This pamphlet also includes enhanced unit descriptions, as Third, digital publication provides an opportunity for well as a discussion of the stratigraphy and structure not regional planners, local, state, and federal agencies, present in the earlier publication. teachers, consultants, and others who are interested in geologic data to have the new information long before a traditional paper map could be published. 1 Stratigraphy corner of the map area (Kfs, see also Blake and others, 2000). Because much of the Franciscan Complex was Mesozoic terrane complexes accreted under the Great Valley complex, which contains the Coast Range Ophiolite, the contact between the two The rock units in the San Francisco Bay region are made Mesozoic complexes is everywhere faulted (Bailey and up of two components: an older set of rocks comprised of others, 1964), and the Franciscan Complex presumably amalgamated, highly deformed tectonostratigraphic underlies the entire San Francisco Bay area east of the San terranes that are displaced, at least in part, from hundreds Andreas fault. to thousands of kilometers from their position of origin Both the Franciscan Complex and the Great (allocthonous or parautochthonous); and a younger, less Valley complex have been further divided into a number of deformed set of rocks that overlie the amalgamated terranes fault-bounded tectonostratigraphic terranes (Blake and and are only offset from their original sites of deposition others, 1982, 1984, 2000, 2002). Within the map area, by offsets of the San Andreas fault system. Throughout strata of three terranes of the Great Valley complex (Blake the map area, the older set of rocks are Mesozoic and the and others, 1984, 2002) crop out. The conglomerates at younger are Tertiary. Black Point (Kgvn) are part of the Healdsburg terrane, The amalgamated Mesozoic terranes can be which is distinguished by the presence of abundant quartz- grouped into three related rock complexes, two of which porphyry and granitic clast conglomerate. The strata and crop out in the map area. One of these, the Great Valley underlying ophiolitic rocks in the Cordelia and Martinez complex, is made up of the Jurassic Coast Range areas are probably part of the Del Puerto terrane, based on ophiolite, which in the map area consists mostly of the presence of large masses of keratophyre. The serpentinite, gabbro, diabase, basalt, and keratophyre extensive outcrops of Great Valley complex strata north (altered silicic and intermediate volcanic rocks), and the and west of Vacaville are laterally equivalent to the type Great Valley sequence, composed of sandstone, area of the Elder Creek terrane, which is characterized by conglomerate, and shale of Jurassic and Cretaceous age. the near absence of keratophyre and the presence of Although the sedimentary rocks and ophiolite are in fault ophiolite breccia in the basal sedimentary strata. contact almost everywhere in the map area, the Great The Franciscan Complex in the map area Valley sequence was originally deposited on top of the comprises two terranes as well as mélange. The ophiolite. This depositional relationship is preserved in southwest corner of the map area is underlain by Late the map area within the Capell Valley quadrangle. This Cretaceous strata (Kfs) of the Novato Quarry terrane. complex represents the accreted and deformed remnants of Metagraywacke (KJfm) of the Yolla Bolly terrane crop out arc-related Jurassic oceanic crust with a thick sequence of in Capell Valley and Sears Point quadrangles. Franciscan overlying turbidites, at least in part related to the North Complex mélange (fsr), which is not a true terrane but is American forearc (parautochthonous). formed by tectonic mixing of rocks of several terranes, The second set of amalgamated terranes composes crops out in the Sears Point and Cordelia quadrangles. the Franciscan Complex, consisting of weakly to strongly The various Mesozoic terranes are described in metamorphosed graywacke, argillite, basalt, serpentinite, detail elsewhere. See Blake and others (2002) for a recent chert, limestone, and other rocks. The Franciscan discussion of the origin of the Coast Range ophiolite and Complex also includes sedimentary-matrix mélange, the Franciscan Complex mélange, as well as a more