mount george final · 2020-07-13 · mount george_final.ai author: cgutierr created date: 9/29/2004...
TRANSCRIPT
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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.