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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

122°07'30"

38°15'00"

Topographic base from

the U.S. Geological Survey

UTM Projection, zone 10,

North American Datum 1927

38°15'00"

122°15'00"

CALIFORNIA GEOLOGICAL SURVEY

MICHAEL S. REICHLE, ACTING STATE GEOLOGIST

122°15'00"

38°22'30"

STATE OF CALIFORNIA- ARNOLD SCHWARZENEGGER, GOVERNOR

THE RESOURCES AGENCY- MICHAEL CHRISMAN, SECRETARY FOR RESOURCES

DEPARTMENT OF CONSERVATION- DARRYL YOUNG, DIRECTOR

122°07'30"

38°22'30"

GEOLOGIC MAP OF THE

MT. GEORGE 7.5' QUADRANGLE

NAPA AND SOLANO COUNTIES, CALIFORNIA: A DIGITAL DATABASE

VERSION 1.0

By

Stephen P. Bezore1, Janet M. Sowers2, and Robert C. Witter 2

Digital Database

by:

Carlos I. Gutierrez1

2004

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

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

} QUATERNARY

} }Pliocene

}}

Holocene

Pleistocene

Miocene} TERTIARY} CENOZOIC

Unit Correlation

Qhcaf

Qoa

Qls

Qt

Qht QhfQha Qhl

QfQa

Qof

Tsv

Tsvr

TsvttTsvbt

} MESOZOIC

CRETACEOUS

JURASSIC

KJgv

Qpf

Th

Tsvsd

Tsvdgi

Jk

sp

TsvdgTsvdgp

Tsvbn

TsvmTsvtr

}}

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

approximately located, dotted where concealed.

Strike and dip of bedding.25

Fault - Solid where accurately located, dashed where approximately located,dotted where concealed.

Axis of anticline

Axis of syncline - Dashed where approximately located, dotted where concealed.

Landslide - Arrows indicate principal direction of movement.

Caldera boundary

Symbol Explanation

Bryant, W.A., 1982, Green Valley Fault: California Division of Mines and Geology Fault Evaluation Report FER-126,

18 p., scale 1:24,000.

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.

Graymer, R.W., Jones, D.L., and Brabb, E.E., 2002, Geologic map and map database of northeastern San Francisco Bay region,

Most of Solano County and parts of Napa, Marin, Contra Costa, San Joaquin, Sacramento, Yolo, and Sonoma counties:

U.S. Geological Survey Miscellaneous Field Studies Map MF-2403, scale 1:62,500.

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.

Sarna-Wojcicki, A.M.,1976, Correlation of late Cenozoic tuffs in the central Coast Ranges of California by means of trace

element geochemistry: U.S. Geological Survey Professional Paper 972, 30 p.

Mankinen, E.A., 1972, Paleomagnetism and potasium-argon ages of the Sonoma Volcanics, California: Geological Society

of America Bulletin, v. 83, p. 2063-2072.

Sims, J.D., Fox, K.F., Bartow, J.A., and Helley, E.A., 1973, Preliminary geologic map of Solano and parts of Napa, Contra Costa,

Marin, and Yolo counties, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-484, scale 1:62,500.

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 1:52,500.

References

UTM GRID AND 1968 MAGNETIC NORTHDECLINATION AT CENTER OF SHEET

0°30'9 MILS

17.5°311 MILS

GNMN

0

0

0

1

1

1.5

.5 2

2

2Thousand Feet

Kilometers

Miles

Contour Interval 20 FeetDotted Lines Represent 5 Foot Contours

2912

INTERSTATE

80

INTERSTATE

780

INTERSTATE

101

American CanyonPetaluma

37

Sonoma

Novato

Mt. George

Napa

Petaluma

Petaluma

River

CuttingsW

harf

Glen Ellen

Cotati

Two Rock

Mapping completed under STATEMAP

FY 2001- 02

FY 2002- 03

FY 2003- 04

121Sears Point

Napa

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

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

Qoa Alluvial 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.

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

and clay that are poorly sorted.

QhcModern stream channel deposits (Holocene <150 years) - Deposits in active, natural stream channels; consists

of loose alluvial sand, gravel, and silt.

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.

TsvSonoma Volcanics, undivided (late Miocene to Pliocene) - Mafic lava flows, breccias, agglomerates, tuff, and tuff

breccia. The age range for the Sonoma Volcanics within this quadrangle is 5.5 to 3.9 Ma (Fox and others,

1985). On the western side of the quadrangle a semi-circular basin rimmed by steep volcanic slopes

partially surrounds the low hills immediately east of Napa. The hills and surrounding basin are known as

the Cup and Saucer. The basin is thought to be a caldera about 7 km in diameter and the low hills a

resurgent volcano near the center of the caldera (Fox and others, 1985). The Sonoma Volcanics are

divided into the following subunits:

Unit Explanation

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

Quaternary units).

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

gently sloping, fan-shaped, relatively undissected alluvial surfaces.

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

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

minor clay.

QofAlluvial fan deposits (early to late Pleistocene) - Alluvial fan sediment composed of weakly cemented conglomerate

and sandstone. Clasts are volcanic, subrounded, and range up to 8 inches in diameter. Topography is

moderately rolling with little or no original alluvial surfaces preserved; deeply dissected.

TsvtrTuff of Rockville - Light-gray to white pumice lapilli tuff and welded pumice lapilli tuff overlain by lithic tuff

breccia. The tuff is exposed in the southeast corner of the quadrangle and below dacite flows along

Monticello Road. Two K-Ar ages for this tuff are 4.8±0.2 Ma on Montecello Road and 4.2±0.04 Ma

northwest of Rockville Park (Fox and others, 1985).

TsvmMafic flows and breccias - Basalt, basaltic andesite and andesite flows and breccias, interbedded with volcanic

agglomerate and tuff.

Great Valley Sequence (Early Cretaceous and Late Jurassic) - Sandstone, pebble conglomerate, siltstone, and

shale.KJgv

TsvrRhyolite ash flow tuff - Black vitrophyre with angular lithic clasts overlying welded tuff with flattened pumice

lapilli and unwelded pumice lapilli tuff. This is the youngest volcanic unit within the quadrangle and

overlies the older rocks with angular unconformity. The age of the tuff is 3.89±0.01 Ma (Fox and

others, 1985).

Dacite of Mt. George - Flows, domes and shallow intrusions of gray to tan porphyritic dacite. The dacite is

typically strongly flow banded. The upper surfaces of flows and the margins of domes and intrusions

are commonly perlitic. The base of the flows is a black porphyritic pitchstone and pitchstone breccia.

K-Ar ages for the dacite are 4.3±0.2 and 3.73±1.23 Ma (Mankinen, 1972; Fox and others, 1985).

Tsvdgp - Pumice breccia, pumice lapilli tuff, and pumice lapilli tuff with lithic fragments and perlitic

glass fragments that mantle flows and domes and occur between dacite flows.

TsvdgTsvdgp

QhlFan levee deposits (Holocene) - Holocene fan sediments deposited as long, low ridges oriented down fan. The

deposits contain coarser material than the adjoining areas.

ThHuichica Formation (early Pleistocene and Pliocene) - Gravel, sand, reworked tuff, and clay. A tuff interbed yields

a K-Ar date of 4.09±0.19 Ma (Fox and others, 1985).

Tsvtt

Tsvbt

Tuff of Tulucay Creek - Pumice lapilli tuff interbedded with tuffaceous volcanic agglomerate. Perlitic glass

fragments are abundant in some tuff beds. Tsvbt - Basalt of Tulucay Creek. Gray vesicular basalt

flow.

TsvdgiDacite intrusion - Gray porphyritic dacite intrusion in Milliken Canyon. The intrusion domed the overlying

volcanic rocks.

Tsvsd Diatomite

TsvbnBreccia of Napa - Dacite breccia underlying the low hills east of Napa. This unit is likely a resurgent volcano

within the caldera.

JkKnoxville Formation (Late Jurassic) - Black shale and thin beds of sandstone. The unit contains only Late

Jurassic fossils (Graymer and others, 2002).

sp Serpentinite (Jurassic)

af Artificial fill (Holocene, historic) - May be engineered and/or non-engineered.

QpfAlluvial fan deposits (late Pleistocene) - Late Pleistocene age is indicated by greater dissection than is present

on Holocene fans; composed of moderately to poorly sorted and bedded gravel, sand, silt, and clay.

QtStream terrace deposits (late Pleistocene to Holocene) - Deposited in point bar and overbank settings where

deposits might be of late Pleistocene or Holocene age; composed of unconsolidated, poorly sorted, clayey

sand and sandy clay with gravel.