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0

0

0

1

1

1.5

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2

2Thousand Feet

Kilometers

Miles

Scale 1:24,000

Contour Interval 40 feetSupplementary Contour Interval 10 feet

National Geodetic Vertical Datum of 1929

UTM GRID AND 2010 MAGNETIC NORTHDECLINATION AT CENTER OF SHEET

MNGN

258 MILS1 MIL

14½° 0°03’

USGSSIM-2858

RUSSIAN R

NAPAR

LakeHennessey

LakeBerryessa

LakeSonoma

C learLake

Yountville

WintersWindsor

Sebastopol

PopeValley

Occidental

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Kelseyville

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Forestville

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Cloverdale

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Jimtown

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29

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116

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Colusa CountyYolo County

Mendocino CountySonoma County

Lake County

Napa County

Solano County

Napa County

123° 122°39°

38°30’

5 Kilometers5 Miles

SOURCES OF MAP DATA

1. Compiled from McLaughlin, 1978, and McLaughlin, undated field sheet; revised Quaternary geology and other minor modifications by Delattre, this study.

2. Modified from Blake and others, 2002, and Gealey, 1951.

3. Compiled and modified from Blake and others, 2002, and geotechnical/fault investigation reports prepared for development within the City of Healdsburg; field mapping by Delattre, this study.

4. Quaternary geology from Delattre, this study; partly modified from Knudsen and others, 2000.

Jimtown 7.5-Minute Quadrangle

128

101

4

1

2

1

2

4

2

3

122°45'0"122°52'30"38°45'0"

38°37'30" rr

Alexander

Val ley

Jim tow n

Blake, M.C. Jr., Graymer, R.W., and Stamski, R.E., 2002, Geologic map and map database of western Sonoma, northernmost Marin, and southernmost Mendocino counties, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-2402, scale 1:100,000, http://pubs.usgs.gov/mf/2002/2402/.

Blake, M.C., Jr., Irwin, W.P., and Coleman, R.G., 1967, Upside-down metamorphic zonation, blueschist facies along a regional thrust in California and Oregon: U.S. Geological Survey Professional Paper 575-C, pp. 1-9.

Blake, M.C., Jr., Smith, J.T., Wentworth, C.M., and Wright, R.H., 1971, Preliminary geologic map of western Sonoma County and northernmost Marin County, California: U.S. Geological Survey Basic Data Contribution 12, scale 1:62,500.

Bryant, W.A., 1982, Fault Evaluation Report FER-135,Chiati, Healdsburg, Alexander, Maacama, and related faults: California Division of Mines and Geology, 21 p.

Bryant, W.A., 1992, Fault Evaluation Report FER-233, Alexander-Redwood Hill Fault, Sonoma County, California: California Division of Mines and Geology, 12 p.

California Division of Mine and Geology, 1983, Jimtown quadrangle, Special Studies Zones, revised official map: State of California, effective July 1, 1983, 1 sheet, scale 1:24,000. Cardwell, G.T., 1965, Geology and ground water in Russian River Valley areas and in Round, Laytonville, and Little Lake valleys, Sonoma and Mendocino counties, California: U.S. Geological Survey Water-Supply Paper 1548, 154 p.

Delattre, M.P., Wagner, D.L., Higgins, C.T., Witter, R.C., and Sowers, J.M., 2007, Geologic map of the Kenwood 7.5’ quadrangle, Sonoma and Napa counties, California: A digital database: California Geological Survey Preliminary Geologic Map, scale 1:24,000, ftp://ftp.consrv.ca.gov/pub/dmg/rgmp/Prelim_geo_pdf/Kenwood_prelim.pdf.

Fox, K.F., Jr., Fleck, R.J., Curtis, G.H., and Meyer, C.M., 1985, Potassium-argon and fission-track ages of the Sonoma Volcanics in an area north of San Pablo Bay, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-1753, scale 1:250,000.

Gealey, W.K., 1951, Geology of the Healdsburg quadrangle, California: California Division of Mines Bulletin 162, 50 p., Plate 1, scale 1:62,500.

Giblin Associates, 1995, Soil and Geologic Investigation Report, Healdsburg Estates Subdivision, Healdsburg, California: Unpublished consulting report, dated March 8, 1995.

Giblin Associates, 1997, Soil Investigation Report, Parkland Farms Subdivision, Healdsburg, California: Unpublished consulting report, dated May 26, 1995 (revised April 28, 1997).

Harding Lawson Associates, 1988, Geologic and Soils Investigation, The Ridge Project, Healdsburg, California: Unpublished consulting report, dated July 1, 1988, 30 p.

Huffman, M.E., and Armstrong, C.F., 1980, Geology for planning in Sonoma County, California: California Division of Mines and Geology Special Report 120, 31 p., scale 1:62,500.

Jim Glomb Consulting, 1996, Response to HTA Review Letter and Report of Supplementary Findings, Roper Property, Giblin Assoc. Job No. 1758.1.2, Healdsburg, California: Unpublished consulting report, dated July 18, 1996, 5 p.

Kleinfelder, Inc., 2004, Geologic and Geotechnical Investigation, Saggio Hills, Healdsburg, California: Unpublished consulting report, dated October 29, 2004.

Knudsen, K.L., Sowers, J.M., Witter, R.C., Wentworth, C.M., and Helley, E.J., 2000, Preliminary geologic maps of the Quaternary deposits and liquefaction susceptibility, nine-county San Francisco Bay Region, California: A digital database: U.S. Geological Survey Open-File Report 00-444, version 1.0, scale 1:62,500, http://pubs.usgs.gov/of/2000/of00-444/.

McLaughlin, R.J., Undated field sheet of geologic mapping on the 7.5-minute Jimtown quadrangle, scale 1:24,000.

McLaughlin, R.J., 1978, Preliminary geologic map and structural sections of the central Mayacmas Mountains and the Geysers steam field, Sonoma, Lake, and Mendocino counties, California: U.S. Geological Survey Open-File Report 78-389, 2 p., 2 sheets, scale 1:24,000.

McLaughlin, R.J., Blake, M.C., Jr., Griscom, Andrew, Blome, C.D., and Murchey, B.L., 1988, Tectonics of formation, translation, and dispersal of the Coast Range ophiolite of California: Tectonics, v. 7, no. 5, p. 1033-1056.

McLaughlin, R.J., Langenheim, V.E., Sarna-Wojcicki, A.M., Fleck, R.J., McPhee, D.K., Roberts, C.W., McCabe, C.A., and Wan, Elmira, 2008, Geologic and geophysical framework of the Santa Rosa 7.5’ quadrangle, Sonoma County, California: U.S. Geological Survey Open-File Report 2008-1009, 51 p., scale 1:24,000, http://pubs.usgs.gov/of/2008/1009/

McLaughlin, R.J., and Nilsen, T.H., 1982, Neogene non-marine sedimentation and tectonics in small pull-apart basins of the San Andrea fault system, Sonoma County, California: Sedimentology, v. 29, no. 6, p. 865-876.

McLaughlin, R.J., and Ohlin, H.N., 1984, Tectonostratigraphic framework of the Geysers-Clear Lake region, California, in Blake, M.C., Jr., editor, Franciscan geology of northern California: S.E.P.M., Pacific section, v. 43, p. 221-254.

McLaughlin, R.J. and Sarna-Wojcicki, Andrei, 2003, Geology of the right stepover region between the Rodgers Creek, Healdsburg, and Maacama faults, northern San Francisco Bay Region - A Contribution to Northern California Geological Society Field Trip Guide, June 6-8, 2003: U.S. Geological Survey Open-File Report 03-502, 23 p., http://pubs.usgs.gov/of/2003/of03-502/.

McLaughlin, R.J., Sarna-Wojcicki, A.M., Fleck, R.J., Wright, W.H., Levin, V.R.G., and Valin, Z.C., 2004, Geology, tephrochronology, radiometric ages and cross sections of the Mark West Springs 7.5’ quadrangle, Sonoma and Napa counties, California: U.S. Geological Survey Scientific Investigations Map SIM-2858, scale 1:24.000, 2 sheets, http://pubs.usgs.gov/sim/2004/2858/.

McLaughlin, R.J., Sarna-Wojcicki, A.M., Fleck, R.J., Langenheim, V., and Jachens, R.C., 2005, Framework geology and structure of the Sonoma Volcanics and associated sedimentary deposits, of the right-stepped Rodgers Creek-Maacama fault system and concealed basins beneath Santa Rosa plain, in Stevens, C. and Cooper, J., editors, Late Neogene transition from transform to subduction margin east of the San Andreas Fault in the wine country of the northern San Francisco Bay Area, California, Fieldtrip Guidebook and Volume Prepared for the Joint Meeting of the Cordilleran Section-GSA and Pacific Section-AAPG, April 29-May 1, 2005, San Jose, California, Fieldtrip 10, Pacific Section SEPM, p. 29-81.

SELECTED REFERENCES

Thrust fault – Sawteeth on upper plate.

Inclined

Inclined – tops of bed known from local features

Overturned

Vertical

Inclined

Vertical

Inclined

Inclined – tops of bed known from local features

Overturned

SYMBOL EXPLANATION

Contact between map units – Solid where accurately located; dashed whereapproximately located; dotted where concealed, queried where uncertain.

Landslide - arrows indicate principal direction of movement.

Fault – Solid where accurately located, dashed where approximately located;short dash where inferred; dotted where concealed; queried where uncertain.Dip of fault shown by arrow normal to fault. Relative horizontal movementshown by arrows parallel to fault. Relative vertical movement shown by U onupthrown block; D on down-dropped block.

?27

UD

?

?

?

Anticline – Solid where accurately located, dashed where approximately located; short dash where inferred; dotted where concealed; queried where uncertain.

Syncline – Solid where accurately located, dashed where approximately located; short dash where inferred; dotted where concealed; queried where uncertain.

Strike and dip of beds Strike and dip of foliation

Strike and dip of volcanic flow unit

25

45

25

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Franciscan Complex

Great ValleySequence

Coast RangeOphiolite

sp spm

Jov

Joi

Jog

KJgvKJgvc

KJgvs

KJfms

Kfss

KJfsKfgwy

Jdb

KJfm

?m

mch

mv ls msssm

ch

cglgs

Jc

?

?

Holocene

}Pleistocene

}

}

Pliocene

Miocene

}}

QUATERNARY

TERTIARY

CRETACEOUS

UPPERJURASSIC

}}

}

CORRELATION OF MAP UNITS

af

adf

Artificial fill (historical) – May be engineered and/or non-engineered.

Qhty

Qhf

Qf

DESCRIPTION OF MAP UNITS

Qa

Artificial dam fill (historical) – Earth dams, rock-fill dams, and embankments constructed to impound water.

Stream channel deposits (modern to latest Holocene) – Fluvial deposits within active, natural stream channels composed of loose sand, silt, and gravel.

Alluvial deposits, undivided (Holocene) – Alluvium deposited in fan, terrace, or basin environments that could not be readily separated for mapping. Typically, consist of poorly to moderately sorted sand, silt, and gravel that form smooth geomorphic surfaces with little to no dissection.

Stream terrace deposits (modern to latest Holocene) – Stream terrace deposits of sand, silt, gravel, and minor clay. Estimated to be latest Holocene in age based on elevation and/or records of historical inundation.

Stream terrace deposits (Holocene) – Sand, gravel, silt, and minor clay deposited in overbank and point-bar settings along streams. Relatively flat surface with little or no dissecting; in study area, generally less than 35 feet above the active channel. Locally divided by relative age (1 = youngest, 2 = oldest):

Alluvial fan deposits (Holocene to latest Pleistocene) – Moderately to poorly sorted deposits of sand, gravel, silt, and clay mapped on sloping, fan-shaped, slightly to moderately dissected, alluvial surfaces.

Alluvial deposits, undivided (Holocene to latest Pleistocene) – Sand, gravel, silt, and clay mapped in small valleys and where separate fan, basin, terrace, and active stream channel units could not be delineated at the scale of mapping.

Qht

Younger Holocene stream terrace deposits.

Landslide deposits (historical to Pleistocene) – Arrows indicate direction of movement; queried where landslide existence is questionable.

Older alluvial deposits, undivided (Pleistocene) – Uplifted or deeply dissected older alluvium, fan, and terrace deposits.

Old alluvial fan deposits (early Pleistocene?) – Limited to a highly dissected, distinctive unit along the southeast side of the Alexander Valley composed almost entirely of angular graywacke and greenstone clasts, with minor chert, and locally, trace rounded clasts of tuff.

Alluvial fan deposits (Holocene) – Sediment deposited by streams emanating from canyons to produce relatively undissected, fan-shaped deposits on alluvial valley floors. Sediments are typically moderately to poorly sorted and composed of sand, gravel, silt, and occasionally clay.

Qhc

Qha

Artificial levee fill (historical) – May be engineered and/or non-engineered.

Artificial channel (historical)

alf

ac

Qls

Qoa

Qof

Qht1

Older Holocene stream terrace deposits.Qht2

Stream terrace deposits (Holocene to latest Pleistocene) – Relatively flat or gently sloping surfaces with slightly to moderately weathered, and slightly to moderately dissected deposits of gravel, sand, silt, and minor clay. Includes strath surfaces cut into bedrock where little or no alluvial deposits remain. Locally divided by relative age (1 = youngest, 2 = oldest):

Qt

Younger stream terrace deposits. Qt 1

Older stream terrace deposits.Qt 2

Terrace deposits (Pleistocene) – Orange to red stained, poorly sorted gravels and sand; clasts vary from subangular to well-rounded and up to small boulder size; derived from a wide range of both Tertiary volcanic and basement lithologies. Age judged from degree of iron oxide staining and weathering, dissection, and elevation above active channel. Locally divided by relative age (1 = youngest, 2 = oldest):

Qpt

Younger Pleistocene terrace deposits. Qpt1

Older Pleistocene terrace deposits.Qpt2

Glen Ellen Formation (early Pleistocene to Pliocene) – Light-brown to yellow-brown, weakly consolidated gravel, sand, silt, clay, and reworked tuff. Sediments are mostly derived from volcanic sources, though pebbles of Franciscan Complex basement are common. Sparse obsidian pebbles are characteristic of this unit. In the Healdsburg area, includes sparse clasts of light-gray rhyolite with distinctive pensile-line flow banding like the “Rhyolite of Adobe Canyon” mapped in the Kenwood quadrangle (Delattre and others, 2007).

QTge

Unnamed fluvial deposits (early Pleistocene to Pliocene) – Weakly consolidated gravel, tuffaceous sand, silt, and clay mapped east of the Healdsburg Fault Zone. Included as part of Glen Ellen Formation in some previous studies, but lacks the obsidian pebbles characteristic of that unit at its type locality and other areas. Includes interbedded lenses of silicic tuff (QTgt), which may represent interfingering with the upper part of Tsvt.

QTgQTgt

Silica carbonate rock (Pleistocene and Pliocene) – Hydrothermally altered serpentinite. Composed of varying proportions of quartz and magnesium carbonate mineral assem-blages ranging from white to green, red and yellow. Commonly associated with mercury and other sulfide mineralization.

sc

Undivided Sonoma Volcanics – Mafic flows, tuffs, breccia, and agglomerate.

Sonoma Volcanics (Pliocene to Miocene)

Tsv

Silicic ash-flow tuff, water-laid tuff, and agglomerate – Tuff is typically light-gray to white, massive, and commonly includes pumice fragments up to 2 inches in diameter. Analysis of samples from near the bottom of Geysers Road yielded Ar/Ar ages of approximately 3.2 to 3.3 Ma, and tephra from just above an underlying basalt flow (Tsb) at the same locality correlates with the Putah Tuff, dated elsewhere at 3.27 to 3.34 Ma (McLaughlin and others, 2005).

Tsvt

Andesite, basaltic andesite, and basalt – Dark-gray to dark-brownish-gray flows and flow breccias, with intercalated tuff and tuff breccia.

Tsvb

Fluvial deposits of lower Geysers Road (early Pliocene to Miocene?) – Pebble to cobble conglomerate, interbedded with poorly sorted sandstone and gray siltstone. Clasts are sub-rounded to well-rounded; composed of material from the Franciscan Complex, ophiolite, and Great Valley sequence, but apparently no Tertiary volcanics. Steeply tilted and folded along the southwest side of the Maacama fault; overlain by approximately 3.2 to 3.3 Ma tuff and mafic flow rock of Tsv.

Tgs

Mudstone, sandstone and conglomerate, undivided (Early Cretaceous and Late Jurassic).

Great Valley Sequence

KJgv

Conglomerate (Early Cretaceous and Late Jurassic) – Predominantly massive, gray to brown cobble conglomerate, with minor thin interbeds of mudstone and sandstone. Clasts are generally rounded to well-rounded, composed of distinctive light-colored rhyolite porphyry, along with welded tuff, granodiorite, quartzite, greenstone, chert, and vein quartz.

KJgvc

Mudstone, shale, and sandstone (Early Cretaceous and Late Jurassic) – Dark-gray to black marine mudstone and shale, with occasional thin interbeds and thicker intervals of greenish-gray sandstone. Sporadic, concretionary carbonate beds locally include Tithonian to Valanginian Buchia, belemnites, and radiolarians.

KJgvs

Franciscan graywacke and mélange, undivided (Late Cretaceous to Early Jurassic) – Predominantly broken and locally sheared, massive to distinctly bedded, gray to green, brown- to orange-weathering, lithic wacke, and dark-gray shale. Also includes areas of mélange (see KJfm) not differentiated from the more coherent graywacke due to gradational contacts, and/or size relative to map scale.

Franciscan Complex, Central Belt mélange (Late Cretaceous to Early Jurassic) – Tectonic mixture of penetratively sheared argillite and graywacke that forms a matrix around more coherent rock masses of varied lithology. Individually mapped blocks differentiated as follows:

Sandstone – Lithic graywacke with minor interbedded black shale. Graywacke is thin- bedded to massive, contains up to 5% detrital K-feldspar, has slight metamorphic fabric, and is locally interbedded with chert and greenstone. Equivalent to parts of KJfs.

Franciscan Complex – Central Belt

KJfs

KJfm

Diabase and diabase-basalt breccias (Late Jurassic) – Coarse breccias composed largely of angular fragments of diabase and basalt, with rare chert; locally cut by diabase dikes. Jdb

ss

Metasandstone of the Douglas Ranch area – Highly folded, foliated, and crenulated glaucophane-muscovite-quartz schist, with relict sedimentary texture suggesting thin-bedded sandstone and shale protolith. Contains prominent accessory fuchsite (green mica); may be correlative with more extensive schist exposed southwest of Skaggs Springs along Warm Springs Creek (McLaughlin, 1978).

ms

High-grade metamorphic rock – Includes metabasalt and metasediments with phyllitic to gneissose texture; largely blueschist grade, and amphibolite to eclogite partially retrograded to blueschist.

m

Limestone – Fine- to coarse-grained, massive and highly recrystallized.ls

Sandstone (Late Cretaceous) – Massive to distinctly bedded, brown-weathering, greenish-gray, white mica- and K-feldspar-bearing feldspathic-lithic wacke and dark-gray shale; locally, the sandstone exhibits incipient foliation. Age based on similarity to fossil-bearing sandstone outside the study area (Blake and others, 2002).

Kfss

Sandstone (Late and Early Cretaceous) – Thin-bedded to massive, buff-weathering, graywacke and minor interbedded black shale; locally interbedded with chert and greenstone. Distinguished from other Cretaceous Franciscan sandstones by the large amount of lithic detritus and apparent lack of K-feldspar (McLaughlin, 1978; Blake and others, 2002).

Kfgwy

Chert – Red, green, and white, thin-bedded chert, with minor interbedded shale and tuff; frequently intermingled with greenstone; contain early Tithonian to early Cenomanian radiolarians.

ch

Conglomerate – Pebble to boulder conglomerate; well-rounded to angular clasts including graywacke, greenstone, silicic porphyry, chert, schist, and vein quartz in matrix of mudstone and graywacke.

cgl

Greenstone – Variably altered and sheared basalt, flow breccias, tuff, and diabase. Dark- greenish-gray to black, weathered dark-brown to orange, predominantly massive, occasionally vesicular, or with pillow structure preserved.

gs

Franciscan Complex – Eastern BeltMetagraywacke (Cretaceous and Jurassic) – Fine- to coarse-grained, highly reconstituted

(textural zone 2 to 3 of Blake and others, 1967), white mica- and glaucophane-bearing metagraywacke, with minor interbeds of low blueschist grade metachert (mch) and greenstone (mv). Locally is a pervasively sheared mélange matrix enclosing high-grade blueschist or amphibolite blocks (m).

KJfms

Serpentinite (Late and Middle Jurassic) – Highly sheared, variably serpentinized ultramafic rocks. Occurs mostly along faults and shear zones, or as isolated blocks within Franciscan mélange and graywacke. Large body along ridge on north side of Healdsburg includes clasts of mudstone from the adjacent KJgvs that suggest emplacement by olistostrome or diapiric intrusion.

Serpentinite matrix mélange (Late and Middle Jurassic) – Fault-bounded slivers of sheared serpentinite enclosing blocks of graywacke, greenstone, shale, and high-grade metamorphic rocks.

Basalt flows and flow breccias of Geyser Peak (Late Jurassic) – Undivided, deeply weathered and altered basaltic rocks, consisting of pillowed flows, breccias, tuff, minor diabase, and minor intercalated tuffaceous chert (Jc) that includes early Tithonian Radiolarian fauna (McLaughlin, 1978).

Jov

Diabase of Geyser Peak (Late Jurrassic) – Fine- to medium-grained, equigranular to porphyritic, intrusive diabase sills.

Joi

Gabbro and diabase (Upper Jurassic) – Fine- to medium-grained, layered olivine- and othopyroxene-bearing gabbro displaying cumulate texture, cut by diabase dikes that increase in abundance in upper part of gabbro; locally cut by dikelets of hornblende-albite pegmatite and lesser biotite-bearing plagiogranite.

Jog

sp

Coast Range Ophiolite

spm

Older fluvial and lacustrine deposits of Little Sulphur Creek (Pliocene or younger) – Conglomerate, sandstone, and siltstone deposited in local, northwest trending strike-slip pull apart basin, truncated on southwest by Maacama fault zone. Locally contains abundant petrified wood, fresh water mollusks and ostracods; conglomerate clasts are subangular to well-rounded and derived locally from the Franciscan Complex, Coast Range Ophiolite, and possibly minor contribution from Great Valley sequence.

Tls

STATE OF CALIFORNIA - ARNOLD SCHWARZENEGGER, GOVERNORTHE NATURAL RESOURCES AGENCY - LESTER A. SNOW, SECRETARY FOR NATURAL RESOURCES

DEPARTMENT OF CONSERVATION - DEREK CHERNOW, ACTING DIRECTOR CALIFORNIA GEOLOGICAL SURVEYJOHN G. PARRISH, Ph.D., STATE GEOLOGIST

GEOLOGIC MAP OF THEJIMTOWN 7.5' QUADRANGLE

SONOMA COUNTY, CALIFORNIA: A DIGITAL DATABASEVERSION 1.0

ByMarc P. Delattre1 and Robert J. McLaughlin2

Digital Database by

Marc P. Delattre1 and Carlos I. Gutierrez1

2010

1. California Geological Survey2. U.S. Geological Survey, Menlo Park, CA

This geologic map was funded in part by the USGS National Cooperative Geologic MappingProgram, Statemap Award no. G09AC00193

38°45'122°45'

38°37'30''122°45'

38°45'

38°37'30''122°52'30''

Topographic base from U.S. Geological SurveyJimtown 7.5-minute Quadrangle, 1993UTM projection, Zone 10, North American Datum 1927

122°52'30''

Copyright © 2010 by the California Department of ConservationCalifornia Geological Survey. All rights reserved. No part ofthis publication may be reproduced without written consent of theCalifornia Geological Survey.

"The Department of Conservation makes no warranties as to thesuitability of this product for any given purpose."

Revised: 8/9/2011

Preliminary Geologic Map available from:http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm