U.S. DEPARTMENT OF THE INTERIOR Open-File Report 2008-1009 U.S. GEOLOGICAL SURVEY Sheet 1 of 3 DESCRIPTION OF MAP UNITS Pamphlet accompanies map 122°37ʹ30ʹʹ 122°45ʹ 38°30 38°30ʹ Tsd Tsd Tst Tst Tgp A' Tsb? 67 Tst bls SURFICIAL DEPOSITS Qoa Tsb Tsb bls Qt Qt 14 sc D 1 fcm fcc fcm Qal U Tst Tgp B'',C'' af Artificial Fill Diatomite and diatomaceous mudstone–The diatom flora in these Contact–Dashed where approximately located; dotted where concealed; 2 Qls Tpd af QTg Qhc 20 Qls Tsb 3 2 25 Jos Tst strata (fossil locality 4) suggest a shallow, eutrophic, neutral to queried where uncertain Tst Tsb Alluvium, undivided (Holocene) Tsb Tsb Qal 30 Qal Qls Tsb Qls Qha slightly alkalic, stagnant lacustrine setting (S. Staratt, written 2 Qhf D? Tsb 54 commun. 2006) Fault–Dashed where approximately located or inferred; dotted where D QTg Qls fcm Tsb 58 fcm U? fcm U U Qt Qhb Basin deposits (Holocene)–Mapped locally, generally includes local silty concealed; queried where uncertain 2 4 Jos Qls 2 Qhf Qls D Qls to muddy alluvial and lacustrine deposits accumulated in low areas Tplg Lignite and lignitic mudstone Qls Tsb Tsb Qal 5 fcm where water is ponded U 6 D Normal fault–Showing geometry of fault plane and sense of slip. Bar and 3 Qal Qls 60 57 Tp Tst Jos Tpwd Silicified (petrified) wood ball on down-dropped block; U on upthrown block; D on down-dropped Qhf 1 Qoa? QTg Qhf Tsb? bls bls Qhc Channels (Holocene)–Incise older deposits block where fault dip unknown. Arrows show direction of relative 42 Tst? Tsb Qal 30 71 Tplm Limestone–Brackish or fresh water depositional setting, locally horizontal movement. Dip of fault plane shown by arrow normal to fault Qal 25 Qpb Tsb 2 7 U D Tsb Qhf Alluvial fan and fluvial terrace deposits, undivided (Holocene)–Gravel, fossiliferous, present as lenses in the upper parts of basaltic andesite with dip amount indicated where known; arrow and number at angle to Qal Qal? Jos 40 Qls Tst fcm sand and silt, derived primarilly from Pleistocene and older flows and breccias fault indicates rake of lineation; diamond astride fault indicates vertical Tst D U 52 Qc bls sedimentary and igneous units, including older Tertiary to Pleistocene dip 1 52 Tsb 45 Qal? 55 Qhf 54 Tst U? 15 70 fcm non-marine gravel, late Tertiary volcanic rocks, and Mesozoic Breccia–Composed dominantly of angular, tectonically slickened clasts 1 Qhf Tst 8 Jos Tprb 9Tst D? Tsb 35 fcv 74 bedrock units of the Franciscan Complex, Coast Range ophiolite and 2 66 af 35 Qls QTg of rhyodacitic rocks with variable textures, interpreted to represent a Thrust fault–Sawteeth on upper plate Tgc 87 70 Tsr Jos 4 10 U Great Valley sequence. Unit may be further subdivided into the fault scarp-derived breccia. Breccia includes clasts up to 3m in a Tgc 10 39 30 Qhpf D Tsb? Qls unmapped D Tsb Tsb 24 Tpd Tsb fcm 47 following units. comminuted matrix derived from rhyodacitic intrusives, flows and Fault lineament–Inferred from linear features on aerial photography; dotted af U Tst 55 Tp 59 af DU Tst? Qls 25 Tpd Jos tuffs. Breccia locally includes: where projected beneath surficial deposits; queried where uncertain. 3 F-3 Tsb 20 F-1 U? Tgc Tsb D? Young Holocene alluvial fan and fluvial terrace deposits–Inset into Qhl 11 Tsb Qhf1 Arrows show relative horizontal motion 1 15 Qal Qal Tsb Tsb 65 U Tsb 12 Tsb old Holocene alluvial fans and fluvial terraces and pre-Holocene Tprg Gravel lenses–Intercalated in breccia, up to ~5m thick, unsorted to Tp 45 D Tsb 13 Tst Tst 25 deposits poorly sorted, un-organized to weakly segregated and cross-bedded. Fault scarp–Showing fault line at base of scarp. Hachures point downscarp 2 10 Qhf Tgp? 75 Qhc U Qc 20 Tst Gravel is composed of rounded to subangular pebbles to cobbles 3 Qhc Tsb Tp? 37 D Qls Qls Tst Qhf Old Holocene alluvial fan and fluvial terrace deposits derived from Franciscan and related Mesozoic sources and from Qal Qls? 14 U? 2 Fold–Dashed where approximately located; dotted where concealed; queried 1 Tsb Tsb 34 Tst D? Qal (Holocene?)–Inset into older Holocene and pre-Holocene deposits older Tertiary volcanics deposited in alluvial fans, debris flows and where uncertain Tsb fcm U Qoa Tst 15 27 talus settings 4 D QTg 48 Tp Tst 60 50 Qls 35 Qhpf 18 Tsb Qhl Natural levee deposits (Holocene) 16 17 Anticline Qls Tst 47 70 18 Qls 21 Tst Qal? Qls Tgp? 2 Qal Alluvial deposits, undivided (Holocene and/or Pleistocene) LATE TERTIARY VOLCANIC ROCKS Syncline Qal Tst Tst Qal U D Tsb Tsb Tgp? 19 Colluvium (Holocene and/or Pleistocene)–Unconsolidated soil and rock 65 Qhpf? 37 Qc Sonoma Volcanics (Pliocene and Miocene)–Rhyolitic to dacitic ash-flow Overturned syncline–Showing dip 1 Qt Tsb 65 Qhpf debris generally transported down-slope by gravitational processes and air fall tuff, andesitic water-lain tuff, and rhyolitic to basaltic flows Tp? Qoa Qhc Tstb Tsb and flow breccia. Regionally, the volcanic section becomes increasingly Minor syncline–Showing bearing and plunge 1 Qhp? 55 Qls Tp Qhp Alluvial deposits, undivided (Holocene and Pleistocene) silicic up-section, and youngs from southwest to northeast, across the Qhf Qhf Rodgers Creek-Healdsburg and Maacama faults (McLaughlin and Tp 25 Closed depression or sag pond Tsb D Qls Tp Tp Tp? U Alluvial fan and terrace deposits (Holocene? and/or others, 2005; Fox and others, 1985). The Sonoma Volcanics consist of Qls? Qhpf Tgp? –Gravel, sand and silt, that commonly includes cobble to the following units. 2 A Qhc 75 Tsb Pleistocene) Strike and dip of beds 85 Qls Qal Qal boulder gravel reworked from Tertiary to Pleistocene non-marine 55 Qhf gravel, from late Tertiary volcanic rocks and from Mesozoic bedrock. Dacitic flows–Mapped near the northeast corner of the Santa Rosa 2 Tsb Tst Tsd 63 Inclined Tst Qhf In Bennett Valley, unit is subdivided into the following. quadrangle and in the southeast half of the quadrangle along the Qpf Tsb af Tgp? Rodgers Creek Fault Zone. The dacite lacks macroscopic quartz or Figure 2. Sources of Geologic Mapping in the Santa Rosa and western Kenwood 7.5' quadrangles. Mapping in parts of Santa Rosa quadrangle began in 1996, together with work in U? D? 42 Inclined–Top of beds known from local features Qt Younger alluvial fan and terrace deposits (Holocene? and/or K-feldspar, commonly contains plagioclase phenocrysts, and rare adjacent quadrangles. The mapping presented here was completed in September, 2005. The sources include: 1. Quaternary geology, from McLaughlin, this study and partly compiled Tp Qhpf? Qha Qhpf1 Qls hornblende and modified from Knudsen and others, 2000; and Witter and others, 2006. 2. R.J. McLaughlin, fieldwork between 1996 and 2005, assisted at times by C. McCabe 2003-05. Area 45 Pleistocene)–Deposits on surfaces inset into older undeformed Qhf2 Vertical Qhc Pleistocene fans and terraces and pre-Pleistocene units sampled for tephrochronology with A.M. Sarna-Wojcicki and for geochronology with R.J. Fleck. Joint traverses at times were conducted with V.E. Langenheim, D.K. McPhee and C.A. Qha Qhf2 Tsb af Rhyolitic and rhyodacitic flows and intrusive rocks–Porphyritic to McCabe during collection of gravity data. 3. Mapping compiled from Jennings, 1988, field checked and locally modified by McLaughlin. 4. Geologic mapping of the Annadel State Qhf Tsr 45 Qhf Qoa 59 Approximate–Determined by sighting from distant location; dip Qhc 2 Qhpf Older alluvial fan and terrace deposits (Holocene? and/or aphanitic, with phenocrysts of quartz and plagioclase. Includes the Park area largely compiled from Higgins, 1983, field checked with minor modifications along SW boundary of park by McLaughlin; sampled for obsidian geochemistry and Qpf 15 af 2 indicated where measured Qoa? Qhpf af Pleistocene)–Deposits on surfaces inset into deformed older rhyodacitic rocks of Zamaroni Quarry (7.26±0.04 Ma), the rhyodacitic geochronology with Sarna-Wojcicki and J. Walker in 1999; again sampled for geochronology of andesites with R.J. Fleck in 2004. Qt Qhf2 Pleistocene and pre-Quaternary rocks rocks of Cook Peak (7.94±0.02 Ma), and perlitic to banded rhyolitic to 85 Qls Qhf Tsb Strike and dip of foliation in sheared or foliated rock 75 Qt Qha Qoa Qt rhyodacitic flow rocks and obsidian in Annadel State Park (4.5±0.01 10 Qls af Tsb 10 Qhf 1 Qoa Qls Landslide deposits (Holocene and Pleistocene)–Deposits varying from Ma) 16 8 Qhc 48 Inclined 15 Qha 17 intact slabs of rock, to unconsolidated rock, soil, and colluvium, that Qhf1 10 Qpf 4 20 Qhpf are displaced down-slope by gravitational processes. Landslides may Tst Rhyolitic to dacitic and minor andesitic pumiceous tuff–Mostly 20 20 Qha Qal vary in area from less than 100 m2 to greater than 1 km2 ash-flows and minor air fall. This unit includes named and unnamed Vertical or near vertical Qls 5 9 Tsb Tsbt 24 tephra layers of different ages in the Sonoma Volcanics (see Tephra data 35 Tsb 12 18 CORRELATION OF MAP UNITS 30 Older alluvium, undivided (Pleistocene)–Generally uplifted and Tables 2.2 and 2.3, figure 2.2, and discussion in pamphlet) 18 Strike and dip of volcanic flow unit 37 Tsb Tsb Tgp? Qoa Qha Qhpf Qt Tsb Qt dissected, isolated surfaces and alluvial fills of small basins, sag Tsb 10 Tsb Crystal-rich rhyolitic to rhyodacitic welded tuff–Welded zones locally F-1 Fossil locality Tsb ponds, and marshes Tstw SURFICIAL UNITS Qhf Qhpf? Qls at tops of tuff layers that are overlain by flows of andesite or basalt Tsb 58 Qhc Qpf Alluvial fans and fluvial terrace deposits, undivided 21 Radiometric dating and tephrochronology localities–Numbers refer to af 10 (Pleistocene)–Gravel, sand and silt in deposits characterized by Tstb Andesitic to rhyodacitic breccia (Pliocene)–Mapped locally in the figures 3A,B and tables 1-3 ? ? ? af 22 unsorted character, a relict fan-like morphology, and their presence northeast part of Santa Rosa 7.5' quadrangle, between the 4.83 Ma Qhf1 Lawlor Tuff and overlying basaltic andesite.