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UTM GRID AND 1980 MAGNETIC NORTHDECLINATION AT CENTER OF SHEET

0°21'6 MILS

17°302 MILS

GNMN

0

0

0

1

1

1.5

.5 2

2

2Thousand Feet

Kilometers

Miles

Contour Interval 20 Feet

Dotted Lines Represent 5 Foot Contours

Scale 1:24,000

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., plate 3A, scale 1:62,500.

Fox, K.F. Jr., 1983, Tectonic setting of late Miocene, Pliocene and Pleistocene rocks in part of the Coast Range North of San

Francisco, California: U.S. Geological Survey Professional Paper 1239, 92 p.

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.

Knudsen, K.L., Sowers, J.M., Witter, R.C., Wentworth, C.M., 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 00-44, version 1.0, scale 1:52,500.

Weaver, C.E., 1949, Geology of the Coast Range immediately north of the San Francisco Bay Region, California: Geological

Society of America Memoir 35, 242 p., plates 6, 10, scale 1:62,500.

Wills, C.J., and Majmundar, H.H., 1999, Landslide hazards in southwest Napa County, California: California Department of

Conservation, Division of Mines and Geology Open-File Report 99-06, scale 1:24,000.

References

2912

INTERSTATE

80

INTERSTATE

780

INTERSTATE

101

American CanyonPetaluma

37

Sonom

a

Novato

Mt. G

eorge

Napa

Petalum

a

Petalum

aRiver

Cuttings

Wharf

Glen E

llen

Cotati

Two R

ock

Mapping completed under

STATEMAP

FY 2001- 02

FY 2002- 03

FY 2003- 04

121Sears P

oint

Napa

GEOLOGIC MAP OF THE

SONOMA 7.5' QUADRANGLE

SONOMA AND NAPA COUNTIES, CALIFORNIA: A DIGITAL DATABASE

VERSION 1.0

By

David L. Wagner1, Kevin B. Clahan2, Carolyn E. Randolph-Loar3 and Janet M. Sowers3

Digital Database

By:

Carlos I. Gutierrez1

2004

Copyright © 2004 by the California Department of Conservation

California Geological Survey. All rights reserved. No part of

this publication may be reproduced without written consent of the

California Geological Survey.

"The Department of Conservation makes no warranties as to the

suitability of this product for any given purpose."

This geologic map was funded in part by the

USGS National Cooperative Geologic Mapping

Program, Statemap Award no. 03HQAG0085

Topographic base from

the U.S. Geological Survey

UTM Projection, zone 10,

North American Datum 1927

STATE OF CALIFORNIA- ARNOLD SCHWARZENEGGER, GOVERNOR

THE RESOURCES AGENCY- MICHAEL CHRISMAN, SECRETARY FOR RESOURCES

DEPARTMENT OF CONSERVATION- DARRYL YOUNG, DIRECTORCALIFORNIA GEOLOGICAL SURVEY

MICHAEL S. REICHLE, ACTING STATE GEOLOGIST

38°15'00"

122°30'00" 122°22'30"

38°15'00"

122°22'30"

38°22'30"

122°30'00"

38°22'30"

1. California Geological Survey, 801 K St. MS 12-31, Sacramento, CA 95814

2. California Geological Survey, 185 Berry St., Suite 210, San Francisco, CA 94107

3. William Lettis & Associates, Inc., 1777 Botello Drive, Suite 262 Walnut Creek, CA 94596

Symbol Explanation

Strike and dip of inclined bedding.25

Landslide - Arrows indicate principal direction of movement, queried where

existence is questionable; hachures indicate headscarp (source area). For

more detailed information on landslides in the Napa County portion of the

Sonoma quadrangle, see Wills and Majmundar, 1999.

Contact between map units - Solid where accurately located, dashed where

approximately located, short dash where inferred, dotted where concealed.

Fault - Solid where accurately located, dashed where approximately located,

dotted where concealed, queried where uncertain. U = Upthrown block;

D = Downthrown block.

25 Strike and dip of inclined foliation.

Vertical bedding.

Vertical foliation.

25Strike and dip of overturned bedding.

Estimated strike and dip of inclined bedding.

Horizontal bedding.

Axis of anticline - Solid where accurately located, dashed where approximately

located, dotted where concealed; arrow indicates direction of plunge.

U

D?

QUATERNARY

Pliocene

Holocene

Pleistocene

MioceneTERTIARY

CENOZOIC

Unit Correlation

Qhcacaf Qhty

QoaQof

Qls

Qt

Qht QhfQha

Qf Qa

Qhly

MESOZOIC

CRETACEOUS

JURASSICKJf KJgv

QTgeQTuTh

Qg

TnrTss Tms

sp

TsvTsvrb Tsvfh

Tsvr

Tsvb

Tsvbb

Tsvam

TsvraTsvas

TsvhTsvt

Tsvm Tsvtp

TsvgTsva TsvtyTsvbp

Tsvib Tsvtl Tsvabsl

unconformity

unconformity

Landslide deposits (Holocene and Pleistocene) - Includes debris flows and block slides. Qls

Unnamed sedimentary deposits (early Pleistocene and Pliocene) - Gravel, sand, reworked tuff, and clay of

uknown age. Sediment derived from Sonoma Volcanics.QTu

Glen Ellen Formation (early Pleistocene and Pliocene) - Gravel, sand, reworked tuff, and clay. Sediments are

derived mostly from Sonoma Volcanics. Contains tephra correlated with the Putah Tuff that is about

3.3 Ma (A. Sarna-Wojcicki, Personal communication, 2004).

QTge

Huichica Formation - (early Pleistocene and Pliocene) - Gravel, sand, reworked tuff and clay. Sediments derived

mostly from the Sonoma Volcanics though there are common Franciscan clasts, with lesser amounts of

clasts from the Great Valley Sequence and Tertiary marine formations. The Huichica Tuff occurs near the

base of the formation along Huichica Creek.

Th

Marine sandstone and mudstone (Miocene) - Light colored well-sorted sandstones, coarse-grained pumice-rich

sandstone, chocolate brown siltstone.Tms

Neroly Formation (Miocene) - Light colored to bluish-gray medium-grained sandstone.

Unnamed tuffaceous siltstone.

Serpentinite.

Tnr

Tss

Alluvium, undivided (latest Pleistocene to Holocene) - Flat, relatively undissected fan, terrace, and basin deposits.Qa

Stream terrace deposits (latest Pleistocene to Holocene) - Sand, gravel, silt and minor clay. Relatively flat,

undissected, stream terraces whose absolute age is uncertain.Qt

QoaAlluvial deposits, undivided (early to late Pleistocene) - Alluvial fan, stream terrace, basin, and channel deposits.

Topography is gently rolling with little or no original alluvial surfaces preserved; moderately to deeply

dissected.

Qof Alluvial deposits (early to late Pleistocene) - Sandy gravel, silt, and clay.

Qha Alluvium, undivided (Holocene) - Alluvium deposited on fans, terraces, or in basins; composed of sand, gravel,

silt, and clay that are poorly sorted.

Qhty Stream terrace deposits (latest Holocene <1,000 years) - Stream terraces deposited as point bar and overbank

deposits along Somona Creek; composed of moderately sorted clayey sand and sandy clay with gravel.

Qhly Levee deposits (Holocene <1,000 years).

QhcModern stream channel deposits (Holocene <150 years)

- Deposits in active, natural stream channels; consists

of loose alluvial sand, gravel, and silt.

ac Artificial stream channel (Holocene, historic).

af Artificial fill (Holocene, historic) - May be engineered

and/or non-engineered.

QhfAlluvial fan deposits (Holocene) - Alluvial fan sediment deposited by streams emanating from mountain drainages

onto alluvial valleys; composed of moderately to poorly sorted sand, gravel, silt and clay.

Unit Explanation

(See Knudsen and others (2000), for more information on

Quaternary units).

QfAlluvial fan deposits (latest Pleistocene <~30,000 years to Holocene) - Sand, gravel, silt and clay mapped on

gently sloping, fan-shaped, relatively undissected alluvial surfaces. Qfc - Fan of Carriger Creek.

QhtStream terrace deposits (Holocene <10,000 years) - Stream terraces deposited as point bar and overbank

deposits along Sonoma Creek; composed of moderately to well-sorted and bedded sand, gravel, silt, and

minor clay.

Franciscan Complex (Cretaceous and Jurassic) - Tectonic mixture of masses of resistant rock including sandstone,

altered mafic rocks (greenstone), an exotic metamorphic rocks embedded in a sheared shaley matrix.KJf

sp

Great Valley Sequence (Early Cretaceous and Late Jurassic) - Mostly greenish, silty mudstone with sandstone

interbeds.KJgv

Tsv

Tsvrb

Tsvfh

Tsvr

Tsvb

Tsvbb

Tsvam

Tsvra

Tsvas

Tsvh

Tsvt

Tsvm

Tsvabsl

Tsvg

Tsva

Tsvty

Tsvbp

Tsvib

Sonoma Volcanics - Mafic lava flows and tuffs, rhyolite to dacite ash flow tuff, lava flows, intrusions, breccia; also

includes tuffaceous sediment, peperite, and hyaloclasite. The age range for the Sonoma Volcanics on this

quadrangle is 7.9 to about 5 or 6 Ma (Fox and others, 1985). The Sonoma Volcanics are divided into the

following subunits:

Tsvb - Olivine basalt lava flows.

Tsvbp - Basalt flows of Boverie Preserve.

Tsva - Andesite lava flows of Mt. Veeder.

Tsvty - White pumiceous tuff; locally contains mudstone clasts from underlying Great Valley Sequence.

Contains an ashflow tuff similar or equvalent to 4.83 Ma Lawlor tuff (Andrei Sarna-Wojcicki and Elmira

Wan, personal communication, 2005).

Tsvg - Fluvial gravel, sand, and silt, occurring beneath Tsva along Cavedale Road.

Tsvrb - Rhyolite of Bismark Knob - Plagioclase phyric, bluish-gray rhyolite and/or dacite tuff. Often has near-

source breccia; some water-laid deposits.

Tsvfh - Lava flows of Huichica Creek - Dark glassy flow rock with highly variable phenocryst assemblage,

including plagioclase, pale olivine, and possible amphibole or pyroxene. Appears to be interlayered with

a plagioclase phyric dacite. Chemical analyses indicate a range of dacitic to trachydacite (Keith Piturka,

personal communication, 2005). Dated by 40Ar/39Ar on plagioclase at 6.64 ± 0.06 Ma (Robert Fleck,

personal communication, 2005).

Tsvbb - Basalt of Bismark Knob - Plagioclase, pyroxene, olivine phyric, flow basalt. Pyroxene phenocrysts

have distinctive yellow alteration.

Tsvh - Hyaloclasite - Well-bedded deposit of angular, vesicular, mafic glass lapilli, with abundant lithic clasts

of basalt, minor andesite and diatomite. Chemical analyses indicate an andesite to trachyandesite

composition (Keith Piturka, personal communication, 2005).

Tsvam - Andesite of Mission Highlands - Gray, plagioclase phyric, andesite interbedded with tuff. Locally

has a platy foliation.

Tsvr - Rhyolite, maybe part of or equivalent to Tsvrb or Tsvra.

Tsvt - Light colored tuff, lithic rich in places. Locally includes tuffaceous, diatomaceous lacustrine sediments.

Includes the tuff of Mt. Pisgah (Tsvtp) along the south fork of Agua Caliente Creek and the tuff of Lovall

Valley (Tsvtl).

Tsvra - Rhyolite of Arrowhead Mountain - Silicic lava flows, domes, and tuffs in the southwest portion of the

quadrangle. A fission track age of 7.5 ± 1.8 Ma was reported by Fox and others (1985).

Tsvib - Basalt plugs and dikes.

Tsvas - Andesite of Schocken Hill - Gray, aphyric andesite lava flows; interbedded with tuff. A fission track

age of 7.9 ± 0.8 Ma was reported by Fox and others (1985).

Tsvm - Mafic flows and breccia - Basalt, andesite, and basaltic andesite.

Tsvabsl - Andesite flow breccia of Stags Leap.

QgFluvial gravel (latest Pleistocene to Holocene) - Gravel deposits composed almost exclusively of Sonoma

Volcanic clasts and fragments of diatomite 10 to 20 cm across.

Preliminary Geologic Map available from:

http://www.conservation.ca.gov/cgs/rghm/rgm/preliminary_geologic_maps.htm

Revised: 03/15/2006