Holocene

Pleistocene

Pliocene(?) 

QUATERNARY

TERTIARY

CENOZOIC

MESOZOIC

CRETACEOUS

OR JURASSIC

CRETACEOUS

JURASSIC(?)

PROTEROZOIC

PALEOZOIC

PENNSYLVANIAN

TRIASSIC

CAMBRIAN

LATEPROTEROZOIC

DEVONIAN

MISSISSIPPIAN

U.S. DEPARTMENT OF THE INTERIORU.S. GEOLOGICAL SURVEY

Prepared in cooperation with the

U.S. FOREST SERVICE (San Bernardino National Forest) and the

CALIFORNIA DIVISION OF MINES AND GEOLOGY

GEOLOGIC MAP OF THE FAWNSKIN 7.5' QUADRANGLE, SAN BERNARDINO COUNTY, CALIFORNIA

Version 1.1

By

Fred K. Miller , Jonathan C. Matti , Howard J. Brown , and Robert E. Powell

Digital preparation by

P.M. Cossette and Gregory Morton 

2001

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3

4

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U.S. Geological Survey904 W Riverside Avenue, Room 202Spokane, WA 99201

U.S. Geological SurveyUniversity of Arizona520 N Park AvenueTucson, AZ 85719

Pluess-Staufer (California) Inc.P.O. Box 825 Lucerne Valley, CA 92356

U.S. Geological SurveyDepartment of Earth SciencesUniversity of CaliforniaRiverside, CA 92521

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Base from U.S. Geological Survey7.5' Fawnskin quadrangle, 1971Lambert conformal conic projection

Geology mapped by F.K. Miller, 1975-1976, 1995-1996; J.C. Matti, 1991-1996; H.J. Brown, 1978-1982; R.E.Powell, 1977

Qof

Qvof

Qof3

Qvof3

Qvof2

Ts4

Ts2

Ts1

1 0 1 MILE 1

2

1 .5 0 1 KILOMETER

CONTOUR INTERVAL 40 FEET

SCALE 1:24,000

GN

MN

DESCRIPTION OF MAP UNITS

Qoa

MODERN SURFICIAL DEPOSITS Sediment recently transported and deposited 

in channels and washes, on surfaces of alluvial fans and alluvial plains, and on 

hillslopes. Soil-profile development is non-existant to minimal. Includes:

Artificial Fill (late Holocene) Sand, gravel, and bedrock from pits and quarries; 

mapped primarily where used for construction of highways and water catchment 

basins

Active-wash deposits (late Holocene) Unconsolidated to locally cemented sand 

and gravel deposits in active washes of streams and on active surfaces of 

alluvial fans. Typically shows fresh flood scours and channel-and-bar 

morphology. Locally includes small areas of older surficial deposits. Most 

deposits are centimeters to a few meters thick

Deposits of alluvial fans (late Holocene) Unconsolidated to locally cemented, 

undissected deposits of gravel and sand that form active parts of alluvial fans. 

Essentially no pedogenic soil development

Deposits of axial valley floors (late Holocene) Unconsolidated to locally 

cemented sand and gravel deposits

Colluvial deposits (late Holocene) Unconsolidated to slightly consolidated sandy 

and pebbly deposits of hillslopes and base of slopes. No pedogenic soil 

development 

Talus deposits (late Holocene) Slightly consolidated to cemented deposits of 

angular and sub angular pebbles, cobbles, and boulders that form scree and 

rubble on hillslopes and base of slopes

Landslide deposits (late Holocene) Slope-failure deposits that consist of 

displaced bedrock blocks and (or) chaotically mixed rubble. Most deposits are 

probably active or recently active

Undifferentiated surficial deposits (late Holocene) Sand and pebble to smallcobble gravel not assigned to any specific surficial materials unit. 

Unconsolidated to moderately consolidated. Includes active wash, colluvium, 

and valley-filling deposits

YOUNG SURFICIAL DEPOSITS Sedimentary units that are slightly 

consolidated to cemented and slightly to moderately dissected. Alluvial fan deposits 

(Qyf series) typically have high coarse:fine clast ratios. Younger surficial units have 

upper surfaces that are capped by slight to moderately developed pedogenic-soil 

profiles (A/C to A/AC/Bcambric

Cox profiles). Includes:

Young deposits of alluvial fans (Holocene and late Pleistocene) Slightly 

consolidated to cemented, undissected to slightly dissected deposits of unsorted 

boulders, cobbles, gravel, and sand that form inactive parts of alluvial fans.

Ts Ts3

Many have unsorted claof Qyf generally form a older:

Young deposits of alluvi

boulder gravel. Unconsgrained. Occupies topog

Young deposits of alluvi

boulder gravel. Unconsgrained. Differs from Q

Young deposits of alluvia

pebble-boulder gravel. coarse grained. Differposition 

Young deposits of alluvia

granule-pebble gravel. 

coarse grained. Differs 

differences in degrees of relative topographic posi

Young deposits of alluvia

Sand and pebble-bouldefine to coarse grained. slight difference in avera

Young deposits of axial vall

moderately consolidated 

Young colluvial deposits (

slightly to moderately co

Young talus deposits (Hol

dissected, consolidated tcobbles, and boulders tslopes

Young landslide deposits (H

that consist of displaceDeposits are probably moderate to strong groun

Young surficial deposits u

Slightly dissected, slight

OLD SURFICIAL DEPconsolidated and slightly to upper surfaces that are capp(A/AB/B/Cox profiles and Bt 

in the range of 10YR 5/4 anreaching 5YR 5/6). IncludesOld deposits of alluvial fan

are moderately consolidfrom younger to older:

Old deposits of alluvial f

dissected alluvial fan degravelly sand, and gradebris-flow fabrics; lenfluvial fabrics are subord

Old deposits of alluvial f

dissected alluvial fan degravelly sand, and gra

debris-flow fabrics

Old deposits of alluvial-va

terraces of gravelly sand

Old talus deposits (late 

consolidated deposits of 

Old landslide deposits (lat

consist of displaced bedrare probably inactive unstrong ground-shaking c

Old surficial deposits undif

dissected, moderately co

VERY OLD SURFICIAL consolidated to indurated, a

capped by moderate to well d

Bt horizons as much as 2 to and 4/4 to 2.5YR 5/6)Very old deposits of alluvi

units that are moderatIncludes from younger to 

Very old deposits of all

dissected. Sandy pebble

Very old deposits of all

consolidated to indurated

Very old landslide deposits 

that consist of displace

Deposits of this unit infSan Bernardino Mountai

Very old surficial deposits

Moderately to well dissein grain size from boulde

Very old deposits of cata

Shattered blocks and fr

processes 

Very old deposits of catastr

and fragmented granitoihighly broken blocks pro

Conglomerate, porphyry - 

Consolidated to indu

conglomerate and congsouth

Conglomerate, Cushenberr

to cemented, very thick bclast type is medium to c

Sandstone and conglomera

to boulder, marble- and medium to very coarse g

Sandstone and conglomer

Consolidated, lithic, acomposition, but dacitic to cobble conglomerate; 

Sandstone and conglomera

Consolidated, lithic, arkmarble. Interbedded sediment source from so

Old Woman Sandstone, m

Pliocene?) Arkosic sanconglomerate, siltstone, 

source from south

Old Woman Sandstone, san

arkosic sandstone interbvolcanic clasts predomifrom north 

Sedimentary rocks south of 

sandstone, pebbly sandstwell consolidated, thin tpale-brown, and brownis

Sedimentary rocks south of 

Two distinct lithologiescemented; medium- to tto coarse-grained sands

greenish-gray. Locally base (Ts) 

Sedimentary rocks of Polig

sandy pebble-cobble coreddish-brown, well conclasts of metaquartzite a

brown and has clasts oterraces cut into unit Ts1

Sedimentary rocks of Ho

Matrix of rock generally angular to round pebblepercent of rock matrix. 

quartzite ranging from locally

Undivided granitic rocks 

granodiorite; ranging to that cannot be assigned grained; massive to folihomogeneous bodies a

generally less than 12. Mhomogeneous bodies anindex ranges from 10 to 

Leucocratic granitic rocks 

leucocratic granitic rock3. Forms dikes, sills, po

too small to map. Incmonzogranite. Rocks associated with Cretaceo

Biotite monzogranite (Cret

monzogranite. Forms sand Deep Canyons. 

phenocrysts; most potColor index ranges frodistributed in rock. Gran

Monzogranite of John B

monzogranite. PotasDistingiushed by uniform feldspar, low color inde

averages about 7; biotdirectional or penetrativCutoff

Monzogranite of Stanfie

Distinguished by consiabsence of other distinc

Biotite is only mafic mfine-grained chilled boLocally has sparse hypidiomorphic-granular

Monzogranite of Butler Pe

biotite monzogranite. F

southwestward. Distinmuscovite. Color inBiotite:muscovite ratio hypidiomorphic-granularby numerous subhorizolandsliding. Completelmonzogranite of Keller P

Monzogranite of Keller Pea

grain size ranges from vcm-long, well-formed, Average color index 9. western part has trace granular; rock has no di

71.1 Ma

Granodiorite of Hanna F

granodiorite. Irregularly phenocrysts. Average cpart; concentration of hoBody probably represen

contaminated where it inAr ages on hornblende 40Ar/39Ar incremental a

written commun., 1996)

JURASSIC

KJl

Ks

Kgc

Kbm

KJdg

Qvof

Unconformity

Ts

Ts

Ts 2 3 Ts4

1 Ts

CORRELATION OF MAP UNITS

Qw Qa

Qyf

Qof

Qof3

Qf Qc

w

Mmy

Mmb

Mml

Dsc

Unconformity

Dsi

Dsv

Qoa

Qaf

Qvof3

Qvof2

Qvobc

QTcp QTcc

QTsc QTscp QTscc

QTom

QTos

Qls

Qyf1

Qyls

Qols

Qvols

Qyf1

Qyf3

Qw

Qa

Qf

Qc

Qaf

Qls

Qyls

Qols

Qvols

Qvobc

Qvobg

QTcp

QTcc

QTsc

QTscp

QTscc

QTom

QTos

Pleistocene(?) and

Plioceneand (or)Miocene(?)

Jb

Jh

Jfc Jc

Jsc

Jdm

Qos

Qos

Contact Solid where located within ±15 meters; dashed where located within ±30 metersContact Separates terraced alluvial units, hachers point towards topographically lower 

surface. Solid where located within ±15 meters; dashed where located within ±30 meters

Fault High angle. Solid where located within ±15 meters; dashed where located within 

±30 meters; dotted where concealed. Hachures indicate scarp; hachures on down-dropped block. Arrows indicate relative movement

Thrust fault Older over younger. Solid where located within ±15 meters; dashed where 

located within ±30 meters; dotted where concealed. Hachures indicate scarp; hachures on down-dropped block

Thrust fault Younger over older. Solid where located within ±15 meters; dashed where 

located within ±30 meters

Fault Variable angle, rotational normal slip, inferred, dashed where located within ±30 

meters

Fault Intruded. Pre-intrusive existence inferredAnticlineOverturned anticlineOverturned syncline

Kh

Jcr

Jd

Qvobg

70

70

70

Strike and dip of primary igneous foliation InclinedStrike and dip of foliation related to faulting InclinedBearing and plunge of linear features Crushed and streaked mineral grains

70

70

70

Strike and dip of beds Inclined Vertical OverturnedStrike and dip of metamorphic foliation Inclined Vertical

 This report is preliminary and has not been reviewed for conformity with U. S. Geological Survey editorial standards. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U. S. Government.  This database, identified as "Digital geologic map of the Fawnskin 7.5Õ quadrangle, San Bernardino County, California" has been approved for release and publication by the Director of the USGS. Although this database has been reviewed and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. This database is released on condition that neither the USGS nor the U. S. Government may be held liable for any damages resulting from its use. 

Qyf

Kh

KJl

Kbm

Ks

Qys

Qys

Qyf2

Qt

Qt Qs

Qs

Qyt

Qyc Qyt

Qyc

Qya

Qya

Qyf4

Qyf5 Qyf5

Qyf4

Qyf3

Qyf2

Qof2

Qof2

Qot

Qot

Qvos

Qvos

Kb

Kb

Kbp

KJb

Kbp

Kk

Kk

LOCATION MAP

15