U.S. Department of the Interior Scientific Investigations Map 3395 U.S. Geological Survey Sheet 2 of 2 Pamphlet accompanies map

CORRELATION OF MAP UNITS 123°15' 123° 122°45' 122°30' A B EXPLANATION 39°45' EXPLANATION Nonmarine basin deposits (Quaternary) CASSZ [See Description of Map Units (in pamphlet) for precise unit ages] 1 NBSFZ PLASKETT Ohlin and others, 2010 Klamath 5 Eureka Volcanics and deposits of Clear Lake area MEADOWS 2 Berkland, 1978; CDWR, 1966, 1968, and 1969 block FUTURE NBSFZ (Holocene–Pliocene) UNCONSOLIDATED DEPOSITS DOS RIOS THATCHER PLASKETT RIDGE RIDGE 3 McLaughlin, R.J., unpublished mapping, 1980–1981 JAMISON RIDGE 6, 15 MFZ Eel River forarc basin (Neogene) 5, 27 4 McLaughlin and others, 1990 Round NSAFZ Crystalline basement rock 5 Jayko and others, 1989; Clark, 1940 Coastal Belt ALLUVIAL TERRACE FAN GLACIAL SPRING VOLCANIC 5, 18 Valley 6 Ohlin H.N., 1989, unpublished mapping, 1985 DEPOSITS DEPOSITS DEPOSITS DEPOSITS DEPOSITS ROCKS Western Transverse Ranges block 7 Hitchcock, C.S., unpublished mapping, 2012–2013; McLaughlin, NBSFZ 21 FELKNER R.J., and Moring, B.C., aerial reconnaissance using Google Earth MAAFZ Central Belt (Upper Cretaceaous and older) SANHEDRIN 1 HILL 5 BRUSHY imagery, 2014 Wilber Springs WILLIS RIDGE MOUNTAIN MOUNTAIN HULL MOUNTAIN Eastern Belt (Upper Cretaceous–Upper Jurassic) KNEECAP RIDGE 8 Etter, 1979; U.S. Forest Service, unpublished mapping Dextral Hook af Qty Qfy Holocene AREA OF 6, 15 MAP 9 Northern Sierra Nevada block Stanford, 1991 Salinian block Coastal Belt (Tertiary and younger) 1 Santa 10 Berkland, 1973 RC-HLDFZRosa Qls Qgd 39°30' Coast Range ophiolite and ophiolitic mélange Qal QUATERNARY 11 Hearn and others, 1995; Sims and Rymer, 1976; Rymer, 1981 Reconstructed 2, 16, LAKE NSAFZ (Lower Cretaceous and Upper–Middle 12 Brown and others, 1981; MacPherson, 1983 Bartlett Springs Qt Qf Qfo 18 18 PILLSBURY Jurassic) Qto synform Qoa 1 12, 13 13 Brown, 1964 FUTURE NBSFZ Qv San Francisco HAY-CAFZ SYMBOLS Pleistocene FOSTER VAN ARSDALE CROCKETT SAINT JOHN STONYFORD 14 Suppe and Foland, 1978; Etter, 1979; U.S. Forest Service, PEAK MOUNTAIN 31-90° MOUNTAIN 2 RESERVOIR unpublished mapping Upper Cretaceous—Neogene clockwise rotation in ? ? 1 15 Qtvo Qfvo Blake and others, 1992 southern Sierra Nevada Batholith and Qsn Qtrv 8 12, 18 25 16 McLaughlin, R.J. and Moring B.C., mapping 2012–2013 Tehachapi Mountains block (Chapman and ? ? 17 Ohlin, H.N., unpublished field work, 1980–1981 others, 2010) FLUVIAL AND LACUSTRINE FILL POTTER 18 McLaughlin and Moring, aerial reconnaissance using Google Earth SAFZ Approximate location of buried tip of Franciscan Monterey 0 10 20 30 KILOMETERS VALLEY 8 imagery, 2012–2014 7 1 tectonic wedge—Barbs on roof thrust side of Pleistocene QUATERNARY 10 FOUTS SPRINGS GILMORE LODOGA 19 Ohlin, H.N., unpublished mapping, 1979–1981 QTc ELK POTATO PEAK 0 5 10 15 MILES wedge Salinian block and Pliocene AND TERTIARY REDWOOD MOUNTAIN 8, HILL 20 McLaughlin, 1978; Ohlin H.N., and McLaughlin, R.J., unpublished VALLEY 12, 13 mapping, 1978–1981 Fault—Arrows show relative movement 16 Southern Sierra MARINE OVERLAP DEPOSITS 9 14, 18 21 Lehman, 1974 Nevada/Tehachapi 39°15' Thrust fault block 22 McLaughlin, R.J., and Moring B.C., minor revisions WW-KCFZ Bakersfield CENOZOIC 2 Tm Miocene 18 23 Lawton, 1956 31-90° Vectors of maximum compression—From 24 Swe and Dickinson, 1970 SG-HFZ orientation of fold axes COW UPPER BARTLETT BARTLETT GARFZ UKIAH HOUGH SPRINGS LEESVILLE Mojave block MOUNTAIN LAKE MOUNTAIN SPRINGS 25 Shervais and others, 2005a, b MAJOR FOLD AXES Te Eocene 3, 16 4, 16, 18 26 Lienkaemper, 2010 18 Antiform 14, 16 27 Clark, 1940 Western Transverse SAFZ Tep Ranges block (present) Synform SALT San Gabriel Tcg 7, 17, 18 CANYON Mountains block 5 Ma 11 4, 16, 18 CLEARLAKE 0 50 100 150 KILOMETERS TERTIARY LAKEPORT 11 LU- BENMORE WILBUR SPRINGS COAST OAKS CANYON 10 Ma LUCERNE 4, 16, 18 0 25 50 75 MILES 15 Ma RANGE 26 GREAT VALLEY COMPLEX OPHIOLITE FRANCISCAN COMPLEX 18 Eocene and 11, 7, 11 39° Paleocene 22 CENTRAL BELT EASTERN BELT 11 CLEARLAKE WILSON Figure 8. Map showing Wilbur Springs Dextral Hook in context of regional structure by northward translation of the Salinian block since the early to middle Miocene. HIGHLAND LOWER Central Belt Mélange Terrane KELSEYVILLE HIGHLANDS VALLEY 23 Rice Valley ELDER CREEK TERRANE SPRINGS 11 LAKE and long-term transpressional deformation along the Northern Bartlett Springs Fault Upper Cretaceous–Paleogene rotations in southern Sierra Nevada-Tehachapi block, ? 19, 20 3, 24 Zone. A, Partial map of California, showing major fault blocks associated with east-vergent crustal wedging, and unroofing of the Franciscan Complex Pomo GLASCOCK 20 Miocene and younger development of the San Andreas Fault, northwestward accompanied shallow subduction of overthickened Farallon Plate and was followed Terrane 3 MOUNTAIN Marin Snow Pickett Peak Mendocino translation of Salinian block, clockwise rotation of Western Transverse Ranges block by northward translation of the Salinian block during the Miocene (Chapman and fcm Headlands- Mountain spo Yolla Bolly Terrane Terrane Pass Terrane (Colgan and others, 2012), and Upper Cretaceous–Neogene clockwise rotation of others, 2010, 2012; Saleeby, 2003; Ernst and McLaughlin, 2012). See text for further b Volcanic c ? Geysers Figure 2. Map showing quadrangles in map area and sources of geologic data. southern Sierra Nevada /Tehachapi block (Chapman and others, 2010). White box discussion. Fault abbreviations: CASSZ, Cascadia Subduction Zone; GARFZ, Garlock ss Terrane Terrane outlines Wilbur Springs Dextral Hook. B, An expanded view of Wilbur Springs Dextral Fault Zone; HAY-CAFZ, Hayward-Calaveras Fault Zone; MAAFZ, Maacama Fault Kuls db Late Hook derived from figures 6 and 7, showing reconstructed Bartlett Springs Synform Zone; MFZ, Mendocino Fault Zone; NBSFZ, Northern Bartlett Springs Fault Zone; ms un Ku Cretaceous and other folds of the dextral hook. Orientations of folds suggest maximum NSAFZ, Northern San Andreas Fault Zone; RC-HLDFZ, Rodgers Creek-Healdsburg cgl v ? ? cgmg uny fym vy compression was ~N. 41° E. to S. 41° W., ±16°. Geometry and approximate timing of Fault Zone; SAFZ, San Andreas Fault Zone; SG-HFZ, San Gregorio-Hosgri Fault Zone; ? smg by cgy cy mspy Wilbur Springs Dextral Hook formation is similar to larger-scale dextral hook formed WW-KCFZ, White Wolf-Kern Canyon Fault Zone. gy lsy ? ? ? fys ? ? ? ? ssm miy oms omv omd psm ? Klcg omg omc omb omun vsm fpp cpp CRETACEOUS SOUTHWEST NORTHEAST vpp ? Kul Kl KJom A A' NORTHWEST SOUTHEAST FEET FEET C–C' dsm Early 6,000 NORTHERN BARTLETT SPRINGS v fcm 6,000 B’–B” c fcm E SECTION SECTION E' Cretaceous v FAULT ZONE Qls fys Qls Qfy QtyQt fpp FEET FEET 4,000 fcm Qls Qal 4,000 Qtvo fys KJom? Qal Josp 4,000 Qal Qal Qal Qal fym fys 4,000 Little Indian Qoa Qt fys? fys Tep Kul Qal KJom ssm ? KJom? Qfo Valley 2,000 2,000 2,000 2,000 ? ? fmp cmp ? KJom fpp Klls SEA LEVEL fys SEA LEVEL SEA LEVEL SEA LEVEL ? ? Kul fym 2,000 fys 2,000 fcm Kssp 2,000 fcm fcm 2,000 fys fym ? 4,000 4,000 4,000 fys 4,000 KJs ? fcm 6,000 6,000 6,000 fym 6,000 fcm _ + ? NORTHERN BAR 8,000 8,000 8,000 TLETT + 8,000 SPRING fcm S FAULT ZONE 10,000 10,000 10,000 _ 10,000

12,000 12,000 12,000 12,000 Jgb MESOZOIC ? ? Late cy cmg Jurassic SOUTHWEST NORTHEAST

B' Snow Mountain

B E–E' B'' FEET Qgd FEET SECTION vsm 6,000 Qls Qgd 6,000 BEND IN SECTION Qal Qtvo vsm fpp Josp fcm? vsm fys Tep 4,000 fys KJom Josp Josp Josp KJs 4,000 cmg c b Ku fcm fym Qty Qfo Qfo Qls Qls fys vsm fys Josp Kl Ku Tep fys Qls Qal Qt Qal fcm Qfo Qfvo vmg Josp 2,000 Qfo Qal Qfy KJom Jov fys Qfo Qty 2,000 Kul fcm fys fcm SEA LEVEL Kl fym SEA LEVEL Joc vpo JURASSIC fym cmg KJs? 2,000 Josp 2,000

4,000 4,000 vpo 6,000 spo _ + 6,000

8,000 NORTHERN BARTLETT SPRINGS 8,000 FAULT ZONE Middle 10,000 10,000 Jurassic

Jov SOUTHWEST NORTHEAST Jod PACIFIC RIDGE Jog C C'

E–E' ANTIFORM Josp FEET NORTHERN BARTLETT FEET ? MIDDLE MOUNTAIN SECTION fys ? 6,000 SPRINGS FAULT ZONE fym vy Qal 6,000 ? SYNFORM fym vy vy Early Lower Blue fym fys 4,000 fys KJom vy 4,000 vy Lake smg Ku QtyQfy fys fys cy Josp Qt Jurassic Josp spo Kl v fys Qal Qfy Qal Qfo Qty fcm Qls Qal Qal fys Jov Qal Qto Qal 2,000 Qal Qfo Qty Qfo Qt Qty Josp KJs 2,000 vmg ? ? SEA LEVEL fpp SEA LEVEL ? vpo Josp ? 2,000 ? 2,000 fcm ? fcm ? ? ? 4,000 4,000 fcm 6,000 _ + 6,000 8,000 8,000 LIST OF MAP UNITS oms Undivided marine clastic rocks, commonly argillitic (Lower vy Metavolcanic rocks (Middle Jurassic, Aelenian or older) 10,000 10,000 See Description of Map Units (in pamphlet) for complete unit descriptions. Cretaceous and Upper Jurassic) mspy Metaserpentinite blocks or lenses 12,000 12,000 Some unit exposures on the printed or plotted map are too small to distinguish omd Diabase, mapped locally the color for unit identification. These units are labeled where possible, and 14,000 14,000 uny Unidentified blocks unlabeled units are attributed in the database. Note that many tiny units, primar- omg Gabbro, mapped locally ily blocks, are covered by symbols. fys Metasandstone and argillite, locally conglomeratic (Upper and omc Radiolarian chert, mapped locally (Upper Jurassic, Kimme- Lower Cretaceous, Cenomanian to Aptian, to Late Jurassic, SOUTHWEST NORTHEAST UNCONSOLIDATED DEPOSITS ridgian) Tithonian) PACIFIC RIDGE af omb Blueschist, mapped locally ANTIFORM Artificial fill (Holocene) cy Metachert (Lower Cretaceous, Albian to Aptian, to Middle D NORTHERN BARTLETT SPRINGS D' Jurassic, Aalenian) FEET MIDDLE MOUNTAIN FAULT ZONE fym FEET Qls Landslide deposits (Holocene and Pleistocene) omun Blocks of unknown lithology 6,000 SYNFORM 6,000 Josp fys Josp Qls fys Qls KJom KJom Qls vy Metavolcanic rocks (Middle Jurassic, Aalenian or older) 4,000 fcm fym Qls fys fys Qls KJs KJs 4,000 Qal Josp Qls ss vy fys Josp Josp fys vy Qls fys Josp fys vy miy ALLUVIAL DEPOSITS COAST RANGE OPHIOLITE Qt? Qal fcm fcm Qal Qal v Qal Qls fym Josp Jov smg vmg vmg smg fcm Qfy Qoa fys Josp miy 2,000 Qal fcm KJs Qal 2,000 Qal Alluvial deposits (Holocene and Pleistocene) Joc Pelagic chert (Upper to Middle Jurassic, Tithonian to Bajocian) Mafic intrusive rocks (Early Cretaceous) Kl? Pickett Peak terrane (Lower Cretaceous, Aptian to Barremian) SEA LEVEL smg fys SEA LEVEL Qoa Jov Older alluvial deposits (Holocene and Pleistocene) Basaltic pillowed flows and flow breccias (Middle Jurassic) fym fpp Undivided metasedimentary and metavolcanic rocks and 2,000 fcm 2,000 Jod Josp TERRACE DEPOSITS Diabase dikes and sills (Middle Jurassic) metachert 4,000 4,000 fys Qt cpp Metachert fcm Alluvial terrace deposits (Holocene and Pleistocene) Jog Gabbro and ultramafic rocks (Middle Jurassic) 6,000 fcm 6,000

vpp + Qty Younger alluvial terrace deposits and surfaces (Holocene?) Josp Serpentinized ultramafic rocks (Middle Jurassic) Basaltic metavolcanic rocks 8,000 _ 8,000 Qto Older alluvial terrace deposits and surfaces (Pleistocene) Mendocino Pass terrane (Lower Cretaceous, Valanginian) 10,000 10,000 FRANCISCAN COMPLEX fmp Foliated metasandstone, argillite, and minor undivided 12,000 12,000 Qtvo Very old alluvial terrace deposits and surfaces (Pleistocene) CENTRAL BELT metachert and greenstone FAN DEPOSITS Central Belt Mélange terrane (lower Tertiary and Upper cmp Metachert and greenstone blocks Qf Alluvial fan deposits (Holocene and Pleistocene) Cretaceous) fcm Undivided mélange (lower Tertiary and Upper Cretaceous) Qfy Younger alluvial fan deposits and surfaces (Holocene?) EXPLANATION OF MAP SYMBOLS EXPLANATION ss Sandstone and argillite (in part, Upper Cretaceous, Ceno- Contact—Solid where location is accurate; long-dashed where Estuarine deposits of Round Valley area associated with former Neogene Qfo Older alluvial fan deposits and surfaces (Pleistocene) manian or younger; middle Cretaceous, Aptian or younger; approximate; short-dashed where inferred; dotted where (Eel River) forearc basin (Middle Miocene) and possibly, Upper Jurassic, Tithonian or younger) Qfvo Very old alluvial fan deposits and surfaces (Pleistocene) concealed. Queried where identity or existence questionable Sandstone and shale, shallow to deep marine, associated with former c Radiolarian chert (Upper Cretaceous to Middle Jurassic) Fault—Solid where location is accurate; long-dashed where Mesozoic–Paleogene Great Valley forearc basin (Eocene and GLACIAL DEPOSITS Paleocene) v Basaltic volcanic rocks (Jurassic) approximate; short-dashed where inferred; dotted where Qgd Glacial deposits, present locally (Pleistocene) concealed. Queried where identity or existence questionable Sandstone shale and conglomerate, marine, and ophiolitic basement and cgl mélange of former Great Valley forearc basin (Upper Conglomerate (Lower Cretaceous and (or) Upper Jurassic Fault Lineament—Inferred from features on aerial photography. P SPRING DEPOSITS R Cretaceous–Middle Jurassic) or younger) Dotted where projected beneath surficial deposits E S Igneous and metasedimentary basement rocks of the Klamath Qsn Hydrothermal deposits (Pleistocene and younger) db Diabase (Cretaceous or Jurassic?) E Tuff of Clearlake Volcanic rocks (Qv)—Mapped in Cache N T Mountains (Jurassic and older) Partially Neogene Eel River Neogene Eel River Formation (QTc) Qtrv Travertine (Pleistocene and younger) ms C forearc basin Metasedimentary rocks (Lower Cretaceous? or younger) exhumed forearc basin O Klamath N FRANCISCAN COMPLEX Active trace of Bartlet Springs Fault Zone (Lienkaemper, rocks of Block V

b E VOLCANIC ROCKS Blueschist blocks (Jurassic) 2010)—Arrows show relative movement. In cross sections: the Central Central Belt (Upper Cretaceaous and older) R

Belt G

circled minus, movement away from observer; circled plus, E Qv Clear Lake Volcanic rocks (Pleistocene) un

Blocks of unknown lithology N Eastern Belt (Upper Cretaceous–Upper Jurassic) movement towards observer T

Coastal

Pomo terrane (Upper Cretaceous to Upper Jurassic) C M FLUVIAL AND LACUSTRINE FILL Coastal Belt (Tertiary and younger) Belt O Strike and dip of beds A A spo Basaltic breccia, sandstone, and shale (Upper Cretaceous, M QTc S R Cache Formation (Pleistocene and upper Pliocene) 40 I G Inclined T O IN Maastrichtean) A MAJOR FOLD AXES C

L E

vpo 40 P Alkalic pillow basalt, pillow-breccias, and minor diabase N MFZ PRESENT

MARINE OVERLAP DEPOSITS A Exhumed rocks of Antiform

Overturned

E

L

the Eastern Belt – and chert (Jurassic) E

Tm P

Sandstone and lignitic shale of the Covelo area (middle Miocene) O

A Synform Horizontal C

E L

Marin Headlands-Geysers terrane (Upper Cretaceous to E N O Te Marine sandstone and shale (Eocene) Lower Jurassic) E C Vertical – E E N smg Sandstone and argillite (Upper Cretaceous, Cenomanian? or O Tep E Sandstone, shale, and conglomerate (Eocene and upper Paleo- C B E Strike and dip of metamorphic fabric in sheared or foliated rocks E younger) L cene) N T STRATIGRAPHIC AND STRUCTURAL RELATIONS 30 E C

cgmg Conglomerate (Upper Cretaceous, Cenomanian? or Inclined O Tcg Rice CONSTRAINING RECONSTRUCTION OF NORTHERN Conglomerate (Eocene and upper Paleocene) C N B

O V Round APPROXIMATE AR younger) Valley BARTLETT SPRINGS FAULT ZONE DISPLACEMENT S N E Round Valley AREA OF FIGURE 7 Vertical V R A TL cmg G Valley GREAT VALLEY COMPLEX Radiolarian chert (Upper Cretaceous, lower Cenomanian to E N E R E T G N T Round Valley Lower Jurassic, Pliensbachian) T Ku Location of block or lens too small to map in broken formation or E Rice Valley T Sandstone, siltstone, and mudstone (Upper Cretaceous, H N S R vmg Basaltic volcanic rocks (Lower Jurassic) mélange P T Cenomanian and younger) U M R

I S a N M Paleogene M Kuls Limestone (Upper Cretaceous) Higher-grade metamorphic rock T aca G Snow Mountain volcanic terrane (Lower Cretaceous, Round Valley A S A A Rice R C R Valanginian or younger?) O N m F G Kul G A Valley Sandstone, siltstone, and mudstone with concretionary limestone Serpentinite A D a I S U vsm I Basaltic to rhyolitic volcanics and intrusive rocks N R F N TA LT Lower Great Valley and conglomerate (Upper and Lower Cretaceous, Ceno- E a u L A Complex Volcanic rock lt manian to Hauterivian) Middle S dsm Diabasic intrusive rocks, largely sill-like B Mountain E L Sandstone Middle Great Valley Complex and T Coastal Miocene ELDER CREEK TERRANE psm Porphyritic basaltic rocks Mountain Coast Range ophiolite Belt T H Middle Kl Siltstone, mudstone, minor sandstone, conglomerate, and Conglomerate R ssm F Mountain Metasandstone and argillite U A Circled areas include Paleogene marine strata deposited on Cretaceous and older sedimentary serpentinite (Lower Cretaceous, Albian to S Coastal T U Great Valley Complex or Coast Range Ophiolite, representing the former westward Hauterivian) Chert L EASTERN BELT Belt Lower T extent of the Jurassic-Eocene Great Valley forearc basin. Round Valley area also Lower includes remnants of Miocene estuarine strata indicating the former southeastern Klcg Conglomerate (Lower Cretaceous, Albian to Hauterivian) Block of unknown lithology Lake Yolla Bolly terrane (Upper and Lower Cretaceous to Upper Lower Lake extent of a Neogene forearc basin (Eel River basin) that formed in the Miocene Klls Jurassic, Tithonian) 58 Lake further to the west (Nilsen and Clarke, 1989). Bioclastic limestone, (Lower Cretaceous, Hauterivian) • Fossil Location—Map number corresponds to table 1 MFZ ~5 Ma fym Mélange of the Yolla Bolly terrane (Upper Cretaceous) Kssp Sedimentary serpentinite (Lower Cretaceous) Hydrothermal bleaching (Quaternary)—Diffuse zone in S by A Blueschist sedimentary and metasedimentary rocks, characterized by quartz, N KJs Argillite, siltstone, and sandstone (Lower Cretaceous, upper A 0 10 20 30 KILOMETERS carbonate, and clay mineral veins and veinlets. Associated with N cgy Valanginian, to Upper Jurassic, Tithonian) Conglomerate D

the Barttlet Springs Fault Zone in the vicinity of Neuman R Jgb Megabreccia (Upper Jurassic, Tithonian to Kimmeridgian) E 0 5 10 15 MILES cy Metachert (Early Cretaceous, Albian or Aptian, to Middle Springs A S

KJom Ophiolitic mélange (Lower Cretaceous) Jurassic, Aelenian) Sinter or silica carbonate rocks F A gy Gabbro U

L omv Mafic volcanic rocks, including pillow basalt, diabase, and • Travertine T noncumulate gabbroic intrusive rocks lsy Limey mudstone A PALEOCENE–EOCENE MARGIN B ~MIDDLE MIOCENE MARGIN C PRESENT MARGIN

Dominated by east-west convergence, following exhumation of Eastern and Central Belts of Franciscan Light-pink transparent overlay delineates former southeastern part of early Miocene and younger (Eel River) Showing major strike-slip faults inboard of the San Andreas Fault, the Mendocino Triple Junction, the Complex from depth of 20–30 km. Yellow circled areas delineate Paleogene deposition near former fore-arc basin based on erosional and tectonic remnants of the former Neogene fore-arc basin that includes present subduction margin, and the remaining offshore and uplifted and eroded onshore Neogene (Eel western margin of the Jurassic–early Cenozoic Great Valley fore-arc basin. yellow-circled Miocene remnant at Round Valley. The Neogene fore arc may have extended much farther to River) fore-arc basin. The present Bartlett Springs Fault Zone extends beyond the Mendocino Triple the southeast (Nilsen and Clarke, 1989) and deposition was on exhumed Franciscan and Paleogene rocks of Junction into the modern subduction margin and dismembers the Bartlett Springs Synform. Round EXPLANATION older Great Valley fore-arc basin. Orientations of synforms and antiforms inboard of the subduction margin Reconstruction of this dismemberment can be used to approximate total dextral displacement and Valley indicate major northeast-southwest transpression that accompanied or postdated Neogene fore-arc approximate a long-term slip rate for the Northern Bartlett Springs Fault. MFZ, Mendocino Fault Zone. Nonmarine basin deposits, undifferentiated (Quaternary) deformation. Slip along the Northern Bartlett Springs Fault is inferred to have right-laterally dismembered the Volcanics and deposits of Clear Lake area (Holocene–Pliocene) Bartlett Springs Synform since middle to late Miocene formation, uplift, and erosion of the Neogene fore-arc basin. See figure 7 for details of slip restoration of the Bartlett Springs Synform. Estuarine deposits of Round Valley area (Middle Miocene)

Sandstone and shale, shallow to deep marine (Eocene and Paleocene) Figure 6. Geologic maps showing progressive deformation of the northern California margin during transition from subduction to right-lateral strike slip. The Northern Bartlett Springs Fault is viewed as having developed since the Miocene from deformation focused along the Bartlett Sandstone and shale, moderately to deep marine, turbiditic (Upper Springs Synform, one of several northwest-trending folds that preceded northward encroachment of the Mendocino Triple Junction and the Cretaceous–Upper Jurassic) San Andreas Fault. The folding formed in response to northeast-southwest transpression across the subduction margin.

Ultramafic and mafic rocks of Coast Range ophiolite and ophiolitic mélange (Lower Cretaceous and Upper–Middle Jurassic)

FRANCISCAN COMPLEX

Central Belt (Upper Cretaceous and older) Mélange EXPLANATION t1 t3 Lake Snow Mountain volcanic terrane A' MAJOR FAULTS Pillsbury N O B' Cross Section B–B’–B’’ R T Active segments of the Bartlett Springs Fault Zone—From aerially Part of structure section B–B’–B“ Part of structure section C–C’ Eastern Belt (Upper Cretaceous–Upper Jurassic) H E R BARTLETT SPRINGS t2-6 N interpreted geomorphic features (Lienkaemper, 2010) BARTLETT SPRINGS PACIFIC RIDGE ANTIFORM

SNOW MOUNTAIN Yolla Bolly terrane (Upper Cretaceous–Upper Jurassic) B FAULT ZONE

FAULT ZONE E–E’ Round A Other faults, undifferentiated—Includes faults mapped in field and VOLCANIC TERRANE R SECTION T Snow Mountain Metasandstone and slaty argillite L ? E BARTLETT SPRINGS Valley T faults inferred from aerial lineaments. Includes faults discussed in Rice T E–E’ E–E’ BEND IN SECTION FAULT ZONE Mélange this report, though not all named faults on figure are discussed SECTION SECTION Valley S P R 0 0 0 Pickett Peak terrane (Lower Cretaceous–Upper Jurassic) I CROSS SECTION ~47 Km N 5 G 1 S A A' Line of structure section ~38 Km MAJOR FOLDS t1 Synform A Line of seismicity cross section—See figure 5, 12 (Sheet 2) and figure 11 (pamphlet) for additional information Eden -5 + -5 -5 Valley 1 Restored Bartlett Springs Synform 2 MAJOR FOLDS + + 4 Middle Mountain Synform Synforms Sa Little Indian nh 1 Bartlett Springs Synform ed Valley 5 Unnamed synform northeast of Rice Valley rin M -10 -10 8/10/16 M 5.1 -10 Reservoir ou 4 Middle Mountain Synform nt main shock 39˚30’ ai 8/10/16 M 5.1 8/10/16 M 5.1 3 Antiform n Depth (km) Depth (km) Depth (km) 5 Unnamed synform main shock main shock

1 2 Pacific Ridge Antiform Antiforms

3 Wilbur Springs Antiform 2 Pacific Ridge Antiform -15 -15 -15 Lake B'' 3 Wilbur Springs Antiform Pillsbury 6 Bartlett Mountain Antiform Logan C' 6 Bartlett Mountain Antiform 4 Springs 4 3 OTHER SYMBOLS EARTHQUAKE EPICENTERS E t1 -20 -20 -20 Faults Magnitude 5.2 earthquake, August 10, 2016 1 Distance (km) Distance (km) Distance (km) B a d Pomo Potter Points used to illustrate range in minimum strike–slip displacement for 5 6 6 Aftershock sequence, August 10, 2016–September 15, 2016

B' Valley

restoration of Bartlett Springs synform configuration t3 R D' i Approximate range in the minimum d t5 t2-6 g B e Epicenters 1984–2014 amount of slip necessary to restore EXPLANATION hypothetical Bartlett Springs synform t4 Structure section E–E’ configuration Middle EARTHQUAKE HYPOCENTERS Mountain PACIFIC RIDGE ANTIFORM STRATIGRAPHIC AND STRUCTURAL RELATIONS t4 8/10/16 M 5.1 main shock

BARTLETT SPRINGS C–C’ 4 t5 B–B’–B“ E' SECTION SECTION CONSTRAINING RECONSTRUCTION OF NORTHERN FAULT ZONE SECTION F BARTLETT SPRINGS FAULT ZONE DISPLACEMENT 8/10/16 through 9/16/16 aftershock sequence U 0 0 TU R E

N Microseismicity 1984–2011 O Round Valley R + TH ER N 4 2 + Fault block motion toward observer

6 B A Paleogene N t5 R O -5 -5 T RT Fault block motion away from observer LE C H T E T R N

S 3 Clear P Bartlett Springs Fault Zone—Arrows show relative R Lower Great Valley +

Lake IN S B G c A strike-slip motion across fault Complex o R S t T t B L s e E F a A T CROSS SECTION T5 (E–E‘) ONLY V r U T -10 -10 a V Lower L l T Miocene l a e l l

Depth (km) Depth (km) Intersections of Northern Bartlett Springs Fault crossing Lake y C e lo S y D P L v itt e RI le R northeast–southwest cross sections t1 (B–B‘–B‘‘), r N e G I s 8/10/16 M 5.1 V S n o 8/10/16 M 5.1

Circled areas include Paleogene marine strata deposited on Cretaceous and older a di

an r ‘ t2-6, t3 (C–C ), and t4, with the plane of

l t

le 6 main shock V main shock y s a Great Valley Complex or Coast Range Ophiolite, representing the former westward lley

g northwest–southwest section t5 (E–E‘)

n extent of the Jurassic-Eocene Great Valley forearc basin. Round Valley area also i r 1 -15 -15 p

includes remnants of Miocene estuarine strata indicating the former southeastern S

B Hypocenters located behind (northeast) of plane of E–E‘ extent of a Neogene forearc basin (Eel River basin) that formed in the Miocene ig Kuikui V B s a or s 39˚00’ lle a o farther to the west (Nilsen and Clarke, 1989). y x r K o L C n Hypocenters located in front (southwest) of plane of E–E‘ o a c k ti e S Ke O nn B UT ed a H y W y E ils R Fa o -20 -20 S N u n 0 10 20 30 KILOMETERS ulp B lt F y hur A a Distance (km) Wa R u Ba T lt t1 t3t2-6 t4 t n L righ k E (H W T u Distance (km) 0 5 10 15 MILES C T n o t ll S in ay P g om R ) i IN G Figure 12. Seismicity cross sections showing hypocentral depth distribution of earthquakes along the Northern Bartlett Springs Fault with plane of t5 is approximated from intersection of the fault’s S Figure 7. Schematic reconstruction of Bartlett Springs Synform configuration prior to its dismemberment along the Northern Bartlett Springs sections t1, t2-6, t3, t4, and t5 (see fig. 5 for locations). Hypocenters are projected into seismicity cross projection in t2-6, t3, and t4 with plane of t5 (magenta hexagon symbol). In seismicity cross sections t1, t3, Fault Zone (fig. 6 B,C). Also shown are other subparallel folds northeast and southwest of the Bartlett Springs Synform discussed in this report. 122˚0’ 122˚30’ sections along lines perpendicular to the sections from ~5 km north and south of the section lines. Depths and t5, we superpose parts of structure sections B–B'–B", C–C', and E–E', respectively, that correspond The restoration suggests a total cumulative oblique dextral slip of approximately 38–47 km for the Northern Bartlett Springs Fault Zone since the of the 8/10/16 main shock and its aftershock sequence are, respectively, the large pink and small orange with the seismicity cross sections. See the structure sections for explanation of lithologic units. Note that middle to late Miocene, based on linking remnants of Paleogene strata deposited along the uplifted and eroded former west margin of the triangles. In t1, t2-6, t3, and t4, post-1984 hypocenters are plotted as small green dots. In section t5, red the axis of a major antiform (Pacific Ridge Antiform) in Franciscan rocks northeast of the Northern Bartlett Paleogene and older Great Valley fore arc. Slip could have begun earlier than the Miocene, however, and total displacement could be >50 km. dots are hypocenters projected into the section from southwest of the plane of the cross section; green Springs Fault Zone forms prominent high topography in the hanging-wall block of the Northern Bartlett See discussions in pamphlet on Wilbur Springs Dextral Hook and Northern Bartlett Springs Fault. Figure 5. Map showing major structural features in map area and locations of structure and seismicity cross sections. dots are hypocenters projected into the section from northeast of the cross-section plane. Intersection of Springs Fault (sections t3 and t5).

Framework Geologic Map and Structure Sections along the Bartlett Springs Fault Zone Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government This plate is offered as an online-only, digital publication. Users should be aware that, because of differences in rendering processes and pixel and Adjacent Area from Round Valley to Wilbur Springs, Northern Coast Ranges, California resolution, some slight distortion of scale may occur when viewing it on a computer screen or when printing it on an electronic plotter, even when it is viewed or printed at its intended publication scale By Digital files available at https://doi.org/10.3133/sim3395 Suggested citation: McLaughlin, R.J., Moring, B.C., Hitchcock, C.S., and 1 1 2 1 Valin, Z.N., 2018, Framework geologic map and structure sections along the Robert J. McLaughlin , Barry C. Moring , Christopher S. Hitchcock , and Zenon C. Valin Bartlett Springs Fault Zone and adjacent area from Round Valley to Wilbur 1 Springs, northern Coast Ranges, California (ver 1.1, September 2018): U.S. U.S. Geological Survey; ISSN 2329-132X (online) Geological Survey Scientific Investigations Map 3395, pamphlet 60 p., 2 2 2018 InfraTerra, Inc. https://doi.org/10.3133/sim3395 sheets, scale 1:100,000, https://doi.org/10.3133/sim3395.