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The San Francisco Bay region includes nine counties surrounding San Francisco Bay and threemajor metropolitan areas: San Francisco, Oakland, and San Jose. The Hayward Fault demarcatesthe eastern side of the topographic San Francisco Bay plain; the East Bay hills extend along the eastside of the fault (fig. 1). Within the map area, the metropolitan division of Oakland-FremontHayward houses a population of approximately 2.5 million people (U.S. Census Bureau, 2006).The map digital files are described in Appendix I. Instructions for viewing and querying the 3Dgeologic map are described in Appendix II.Geologic BackgroundMesozoic terrane complexesA tectonostratigraphic terrane is a fault-bounded body of rock that has a geologic history thatdiffers from those of adjacent rock bodies (Jones and others, 1983), implying some amount ofdisplacement from its original position in order to juxtapose dissimilar rock bodies. Associatedterranes (that is, terranes that share some common aspects of their geologic history) are groupedinto terrane complexes. The Mesozoic rocks in the study area are composed of two terranecomplexes (Blake and others, 1984; 2000; Graymer and others, 1996), the Franciscan Complex andthe Great Valley complex (fig. 2). Each terrane complex comprises several related terranes (Blakeand others, 1984).The Great Valley complex is composed of at least five terranes, two of which crop out in the studyarea (the Healdsburg terrane and the Del Puerto terrane). Each terrane in the Great Valley complexis made up of Middle-Late Jurassic ophiolitic rocks (called collectively the Coast Range ophiolite),with or without Late Jurassic silicic volcanic rocks, and with one exception, is depositionallyoverlain by Late Jurassic and Cretaceous sedimentary strata (called cumulatively the Great Valleysequence). Although the origin of the Coast Range ophiolite remains controversial (see Dickinsonand others [1996] for a summary of three different theories of Coast Range ophiolite origin), weherein accept the origin outlined in Graymer (2005) and Graymer and others (2006); the CoastRange ophiolite formed in the forearc of an oceanic island arc outboard of the North Americancontinental margin, and the island arc and the forearc-related ophiolite were subsequently accretedto North America during the late Kimmeridgian Nevadan Orogeny (approximately 151-153 Ma).The earliest Great Valley sequence strata vary between terranes, but the bulk of Great Valleysequence sediments are thought to derive from a continental margin arc associated with the SierraNevada batholith (Ojakangas, 1968; Dickinson, 1970).The Franciscan Complex is composed of many terranes, plus mélange (a chaotic mix of rocksderived from multiple terranes). In the study area, four coherent terranes (Yolla Bolly, AlcatrazIsland, Marin Headlands, and Novato Quarry terranes), as well as mélange, crop out (Blake andothers 1984; Graymer, 2000). Each coherent terrane in the Franciscan Complex is made up of oneor more types of seafloor rocks (mid-ocean ridge basalt, seamount basalt, pelagic limestone and(or) chert, turbidite-derived sandstone and shale) accreted and amalgamated in a subduction zone(Ernst, 1969). The emplacement in the subduction zone has resulted in a low T/high Pmetamorphic overprint on some Franciscan Complex terranes ranging from incipient developmentof low T/high P minerals to complete metamorphism to glaucophane schist. Many FranciscanComplex terranes, however, have undergone only low-grade metamorphism, evidently nottraveling deep into the subduction zone before being accreted to that overlying crust. For most of6

Cenozoic OverlapCzsCzsCzvCzvCenozoic sedimentary rocksCenozoic volcanic rocksGREAT VALLEY COMPLEXfsrCzvHealdsburg terraneSedimentary rocks (Great Valleysequence)Coast Range ophiolite and keratophyreCoast Range ophiolite, San Leandrogabbro memberghsghsfyb CzvghoghoghogghogghsfnFRANCISCAN COMPLEXfnfnfaifaifmhfmhfybfybfsrfsr( )CzsfnUndifferentiated Great Valley complexCoast Range ophioliteguoguoPointPinolefsrDel Puerto terraneSedimentary rocks (Great Valleysequence)gdsgdsSan PabloBayfsrmixedfsrNovato Quarry terraneAlcatraz Island terraneMarin Headlands terraneYolla Bolly terraneMélangeparantheses indicate unit is coveredConcealed faultMajor faults of the Hayward Fault ghooiscncran F Bay116 W120 42 N1010 milesghog(fai)SanLeandro(guo)gdsgdsHayward0 100 200 km20 km0SaSanFrancisco124 WNghs(fmh)Area of mapghsSanFrancisco(guo)CA38 (fyb)LIRNCzsIA34 NfsrFremontFOArea ofFigure 2CzsfsrfybLos AngelesSan JoseFigure 2. Generalized terrane map of the Hayward Fault zone (modified from Graymer and others, 2005).7

the history of Franciscan accretion, the terranes have accumulated in the subduction zone’s westernmargin of the North American Plate (a process that may be continuing today at the active Cascadiasubduction margin to the north). However, Graymer (2005) showed that the age of the oldestFranciscan Complex metamorphic rocks suggest that these rocks were subducted into the trenchassociated with the island arc outboard of the North American subduction margin, and were carriedto North America along with the island arc and forearc as described above.The subduction emplacement of the Franciscan Complex means that Franciscan Complex terraneswere originally all structurally under the Great Valley complex (although this position has beenlocally reversed by later tectonics as explained below). This juxtaposition allowed some admixtureof materials of the two terrane complexes. Specifically, serpentinite from the base of the CoastRange ophiolite (Great Valley complex) is found entrained in the Franciscan Complex mélange,whereas high-grade metamorphic blocks (Franciscan Complex) are found entrained in serpentinitematrix mélange that is associated with the Coast Range ophiolite. Previous workers have includedserpentinite as a component of the Franciscan Complex, but the absence of middle-lower oceaniccrust rocks in coherent Franciscan Complex terranes, as well as the plate tectonic model fromFranciscan Complex terrane emplacement, suggests that the base of the downgoing (FranciscanComplex bearing) slab was entirely subducted, and that all serpentinite in the California CoastRanges was originally part of the upper plate (Coast Range ophiolite). The emplacement ofFranciscan Complex terranes beneath the Great Valley complex also implies that FranciscanComplex rocks exist at depth beneath exposed Great Valley complex rocks at least as far east as theGreat Valley margin.Paleogene unroofing and overlapAlthough subduction and Franciscan Complex accretion at the western margin of the NorthAmerican Plate continued into Neogene time, based on the presence of Miocene marine fossils insome Franciscan Complex terranes several hundred kilometers north of the study area (McLaughlinand others, 1996), accretion of the bulk of Franciscan Complex terranes was probably complete byabout the end of the Cretaceous Period. Tectonic and(or) erosional unroofing of the FranciscanComplex terranes, as evidenced by the presence of Franciscan Complex detritus in Tertiary strataoverlying Great Valley Sequence rocks, began in Paleocene time (Berkland, 1973) and waswidespread by Eocene time (based both on the presence of Franciscan Complex detritus in Eocenestrata and the presence of Eocene strata unconformably overlying Franciscan Complex rocks).Therefore, although certainly modified by later tectonics, the basic amalgamation of the two terranecomplexes (Franciscan and Great Valley) was complete by Tertiary time. As a result, for this 3Dmap we treat all Tertiary strata in the San Francisco Bay region (except Tertiary FranciscanComplex terranes in northwestern Sonoma County) as an overlap sequence (that is, strata formedafter amalgamation of separate terranes and deposited over both of the older units), even though theoldest units that are actually observed to be deposited on both terrane complexes are middleMiocene marine strata in the East Bay hills, the hills just east of the cities of Berkeley, Oakland,San Leandro, and Hayward (fig. 1) (Hall, 1958; Graymer and others, 1996).Neogene transpression and development of the San Andreas Fault systemStarting about 30 Ma, the subduction zone at the western North American plate margin began toconvert to the present transpressional margin during the formation and migration of two triplejunctions, the Mendecino Triple Junction and the Baja Triple Junction (McKenzie and Morgan,1969; Atwater, 1970; Atwater and Stock, 1988). In northern California this conversion resulted in8

three major structural developments: the San Andreas Fault, a series of volcanic fields, andwidespread compressive deformation. First, the largely strike-slip San Andreas Fault System wasformed as the northwestward migrating Mendocino Triple Junction passed northern California.This system is made up of multiple faults, which jointly have accomodated at least 450 km of rightlateral offset over the past 23 m.y. (Matthews, 1976; Clark and others, 1984). In much ofCalifornia about two-thirds of strike-slip offset has been taken up by the San Andreas Fault itself,but in the San Francisco Bay area, the fault system is complex and some strands of the presentlyactive San Andreas Fault have taken up as little as 28 km of right-lateral slip (Cummings, 1968;Jachens and Zoback, 2000). About 175 km of the total strike-slip offset on the San Andreas Faultsystem has been taken up in the past 12 Ma by faults in the East Bay (Jones and Curtis, 1991;McLaughlin and others, 1996; Jachens and others, 1998), including about 100 km of offset on theHayward Fault and about 50 km of offset on the Miller Creek-Moraga-Pinole Fault systems in thestudy area (Graymer and others, 2002a).Second, in the wake of the migrating triple junction a northward-younging series of volcanic fieldswas developed (Fox and others, 1985). Many of these volcanic fields formed at or near the largelystrike-slip faults of the San Andreas Fault System, and as a result parts of these volcanic fields havebeen widely separated; offset of correlated volcanic fields provide one of the primary controls onthe amount and timing of fault offset.Third, the late Neogene has been a time of widespread compressive deformation throughout theCoast Ranges (Suppe, 1977; Namson and Davis, 1984; Miller, 1999). Some of the compressionhas resulted from restraining bends and stepovers in the largely strike-slip faults (for exampleAndrews and others, 1993), but there is also a regional component of fault-normal compression asevidenced by 1) the uniformly compressed folded and reversely faulted Neogene strata in theregion (Page, 1982), 2) a reverse-offset component of fault motion on some of the San AndreasFault system, and 3) basement wedge-faulting (Wentworth and others, 1984; Unruh and Moores,1992).The results of the combined compressional and transform deformation in the San Francisco Bayregion include two important developments. First, fault offset has juxtaposed structural blocks ofdiffering stratigraphy (miniature terranes termed stratigraphic assemblages by Jones and Curtis,1991). Second, during the Neogene, the present north-northwest trending ridges developed in theCoast Ranges (Dibblee, 1966; Vanderhurst and others, 1979; Jones and others, 1994; Graymer,1995). The Berkeley-Oakland Hills in the study area were probably uplifted in Quaternary time,based on the presence of Pleistocene alluvial gravels near the ridge tops in the Oakland Hills, thehills just east of the city of Oakland (fig. 1) (Graymer, 2000).MethodsThe methods used to construct the 3D geologic map combined geologic mapping with geophysicalmapping techniques. Geologic mapping techniques included the mapping of surface geology andinferring the sub-surface geology using down-dip projections and the surface geologic mappatterns. Geophysical techniques were used to investigate the primarily unobservable subsurface.Geophysical techniques included seismic reflection and refraction surveys, tomography, andpotential field surveys. Potential field surveys, especially gravity and magnetic data, which offeredbroad areal coverage, were used extensively to define geologic structures in this model (figs. 3 and4). Several mapping techniques were applied in a complimentary fashion to maximize theeffectiveness of each piece of evidence for different portions of the model; five areas in particular,the Hayward Fault, the east hills area (the hills just east of the cities of Berkeley, Oakland,9

122 30'0"W122 15'0"W122 0'0"W121 45'0"W38 15'0"N38 15'0"NSan PabloBay basin38 0'0"N38 0'0"N3D map boundarycoastline37 45'0"N37 45'0"NCalaveras F.Hayward F.Rodgers Creek F.mGal31 - 36San Leandrobasin26 - 3021 - 2516 - 2011 - 156 - 101-5-4 - 0-9 - -5-14 - -10-19 - -1537 30'0"N37 30'0"N-24 - -20-29 - -25-34 - -30-39 - -35-44 - -40-49 - -45Evergreenbasin-54 - -50-59 - -55-67 - -60122 30'0"W122 15'0"W00122 0'0"W2551015121 45'0"W50 Kilometers2025 MilesFigure 3. Isostatic residual gravity anomaly map of the study area. Data fromRoberts and Jachens (1993) and unpublished gravity data.10

122 30'0"W122 15'0"W122 0'0"W121 45'0"W38 15'0"N38 15'0"NTv38 0'0"N38 0'0"N3D map boundarycoastlineRodgers Creek F.Calaveras F.JgbHayward F.37 45'0"NnT37 45'0"N261 - 280241 - 260221 - 240201 - 220181 - 200161 - 180141 - 160121 - 140101 - 12081 - 10061 - 8041 - 6021 - 401 - 2037 30'0"N37 30'0"N-19 - 0-39 - -20-59 - -40-79 - -60-99 - -80-119 - -100-139 - -120-159 - -140-482 - -160122 30'0"W122 15'0"W00122 0'0"W2551015121 45'0"W50 Kilometers2025 MilesFigure 4. Magnetic anomaly map of the study area. Labels indicate the magneticanomalies that helped define the volcanic rocks of uncertain age (Tv) and the rocksof the Coast Range ophiolite (Jgb). Data from U.S. Geological Survey (1999).11

San Leandro, and Hayward, fig. 1), the Quaternary deposits and Tertiary volcanic deposits, the SanLeandro gabbro of Ponce and others (2003), and the Mesozoic terranes west of the Hayward Fault,represent the full spectrum of mapping techniques used to make the 3D geologic map.Hayward FaultThe Hayward Fault is represented in the map as a single surface, ignoring the possibility ofmultiple active strands in a finite width fault zone. This surface was created using two data sets:(1) the mapped trace of the creeping Hayward Fault (Lienkaemper, 1992), and (2) the locations ofhypocenters of earthquakes from 1984-2000 relocated using the double-difference technique(Waldhauser and Ellsworth, 2000; Ponce and others, 2004). Software tools were used to project thefault trace onto the earth’s surface, as defined by USGS 30-meter digital elevation models. Usingmap view slices spaced 1.25 km apart in depth, and cross-section slices perpendicular to the faultspaced 1.25 km apart along the fault, a set of curves, representing the fault trace in each profile,was constructed and adjusted by eye, honoring insofar as possible the surface fault trace data andthe hypocenter data. Simpson and others (2003) show a set of sections at 2.5 km spacing, givingsome impression of the hypocenter density along the fault. In places with few or no earthquakes, itwas necessary to interpolate and extrapolate using the nearest clusters of events. When faced withambiguities and complexities, our choice was to opt for a simple, smooth surface consistent withmost hypocenters. In places where there were hints of multiple active strands, the surface wasmade to pass through either the better defined strand or the strand that resulted in a morecontinuous overall surface. Adjustments were made in an iterative fashion, alternating betweenmap views and cross-section views, so that interpolations and extrapolations in both horizontal andvertical directions would be consistent. The curves were then sampled at 1.25 km intervals, togenerate a set of xyz points. The final set of xyz points was then imported into EarthVision (Dynamic Graphics Inc.) to create the Hayward Fault surface using interpolation routines providedin the software. Additional control points were added as required, based on geologic reasoning, toremove artifacts created by the interpolation algorithm in areas of poor data control.East Hills AreaEast of the Hayward Fault, pre-Quaternary strata are exposed by the east-side-up component ofmotion within the fault zone. The strata are deformed; tight, complex folds and many minor faultsresult in a complicated ge

The Hayward Fault (fig. 1) is one of three major faults of the San Andreas Fault System that has produced large (M 6) historic earthquakes in the San Francisco Bay area; the other major faults are the San Andreas and Calaveras Faults. The Hayward Fault roughly bisects the San Francisco Bay