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CALIFORNIA GEOLOGICAL SURVEYJOHN G. PARRISH, Ph.D., STATE GEOLOGIST
CGS SPECIAL REPORT 217, PLATE 4GEOLOGIC COMPILATION OF QUATERNARY SURFICIAL DEPOSITS IN SOUTHERN CALIFORNIA
WEST HALF OF BLYTHE 30' x 60' QUADRANGLESTATE OF CALIFORNIA - ARNOLD SCHWARZENEGGER, GOVERNOR
THE RESOURCES AGENCY - LESTER SNOW, SECRETARYDEPARTMENT OF CONSERVATION - BRIDGETT LUTHER, DIRECTOR
GEOLOGIC COMPILATION OF QUATERNARY SURFICIAL DEPOSITS IN SOUTHERN CALIFORNIAWEST HALF OF BLYTHE 30' X 60' QUADRANGLE
MAP REFERENCES
MAP EXPLANATION
DIGITAL GEOLOGIC DATA FILES USED IN GIS COMPILATION OF QUATERNARY UNITS Stone, P., 2006, Geologic map of the west half of the Blythe 30' by 60' quadrangle, RiversideCounty, California and La Paz County, Arizona, http://ngmdb.usgs.gov/Prodesc/proddesc_76909.htm: U.S. Geological Survey, Scientific Investigations Map 2922, scale 1:100,000.
REFERENCES USED IN PREPARING LEGENDS AND MAPS FOR QUATERNARY UNITS Matti, J.C., and Cossette, P.M., 2007, Classification of surficial materials, Inland Empire Region,southern California: conceptual and operational framework: U.S. Geological Survey, Open-File Report(in progress). Southern California Areal Mapping Project (SCAMP), 2000, A proposed classification for surficialgeologic materials in southern California, version 1.0. U.S. Geological Survey and California Division of Mines and Geology, 2000, Classification of Quaternary deposits, Southern California Areal Mapping Project (SCAMP), a working model, version 1.0:(09/10/2000).
West Half of Blythe Quadrangle The west half of the Blythe quadrangle is primarily desert terrain consisting of mountain ranges surroundedby extensive alluvial fans and plains. While the majority of the quadrangle is sparsely populated, populationcenters are present on the Palo Verde Mesa and along the Colorado River flood plain in the southeast corner ofthe quadrangle. Located in the Colorado Desert Province, most of the land surface is comprised of Quaternaryalluvial deposits either derived from the local mountain ranges or transported into the area by the ColoradoRiver, which forms the eastern boundary of the quadrangle (Stone, 2006). The three main northwest-oriented,low-relief mountain ranges in the quadrangle (McCoy Mountains, Little Maria Mountains, and Big MariaMountains), and the northeast-trending Palo Verde Mesa, in the south central portion of the quadrangle, areseparated by broad alluvial valleys. Alluvial deposits in Chuckwalla Valley, west-southwest of the McCoyMountains, and in the McCoy Wash, in the central portion of the quadrangle, are primarily of Pleistocene ageadjacent to the mountain ranges and Holocene age in the central portions of the valleys. The Pleistocenedeposits form smooth, varnished pavements, whereas the Holocene deposits form rougher surfaces that preserverelict depositional bars and channels (Stone, 2006). The youngest locally derived alluvium in these valleys isthat of the modern washes, which are commonly incised many meters into the older alluvial fan deposits (Stone,2006). Several older Quaternary units, composed largely or entirely of alluvium deposited by the ColoradoRiver when it flowed across the area at much higher elevations, are present on the Palo Verde Mesa, in thevicinity of the Mule Mountains, and along the Colorado River flood plain. Various episodes of sedimentdeposition during Holocene time are also evident along the modern flood plain of the Colorado River. OtherHolocene deposits within the quadrangle include wind-blown sands and dry lake bed deposits. Partiallystabilized, east- to southeast-trending Holocene sand dunes are present in Rice Valley, in the northern portionof the quadrangle, and in parts of Chuckwalla Valley. Fine-grained Holocene playa (dry lake) sediments thatlack evaporites (salts) are also found in Chuckwalla Valley (Stone, 2006). In preparing this derivative map of the west half of the Blythe 30’ x 60’quadrangle, CGS used geologicsource data compiled in digital format by Stone (2006). CGS retained the boundaries of Quaternary age surficialdeposits shown on the source map with very few revisions. Quaternary surficial deposits on the source map arerepresented on this map by 11 of the 28 generalized project derivative units; boundaries of more detailedsource map subdivisions are shown without label within the generalized derivative unit. This indicates moredetailed geologic information is available in the Source GIS Database. For example, an area designated Qvof(very old alluvial fan deposits) on this map may have been further divided on the source map into several unitsto distinguish different depositional surfaces and compositions. Bedrock units identified by Stone (2006) are
July 2010
Cheryl A. Hayhurst, PG and Trinda L. Bedrossian, CEGCompiled from existing sources by
Solomon McCrea and Barbara WanishDigital preparation by
A Project for the Department of Water Resources by the California Geological Survey
This map of Quaternary surficial deposits in the west half of the Blythe 30’ x 60’ quadrangle was compiled bythe California Geological Survey (CGS) for the Department of Water Resources (DWR) to assist in identifying whereflooding and deposition of sediment occurred in the geologically recent past. The east half of the Blythequadrangle extends east into La Paz County, Arizona and is not addressed as part of this project. The focus ofthis project is on Quaternary (Q) surficial deposits (less than 1.8 million years) on alluvial fans, floodplains,and in basins where such deposits are subject to a number of geologic hazards including flooding, amplification ofseismic shaking, liquefaction, and collapsible soils. In general, areas of most recent deposition during LateHolocene time (within the last 500 years) have a greater potential to be areas of future flooding and depositionthan those underlain by older surficial deposits. Project Overview The west half of the Blythe 30’ x 60’ quadrangle represents one of several 100,000 scale quadrangles includedin the detailed Geographic Information System (GIS) based geologic data set compiled by CGS from recent highresolution geologic mapping available for southern California. The GIS database merges more than 2100 geologicunits from source maps published primarily by the U.S. Geological Survey (USGS) and by CGS (Source GIS Database)into a common format that depicts 40 derivative categories of surficial deposits and bedrock for the entire area(Derivative GIS Database). Quaternary surficial deposits are divided into 28 categories modified from themethodology of Matti and Cossette (2007), the Southern California Areal Mapping Project (SCAMP, 2000), and theUSGS and California Division of Mines and Geology (2000). While specific variations in age and physical propertiesexist within units on each source map, CGS retained the basic premise of Matti and Cossette (2007) that surficialdeposits within each of the Quaternary derivative map units formed during a particular range of geologic time, have asimilar origin, and have generally similar physical properties. Within the 28 derivative units, progressively older surficialdeposits are typically better consolidated and more highly dissected by erosion, have more developed and/oreroded soil profiles with stronger degrees of weathering and surface armoring, and occupy a higher topographicposition within alluvial fan and floodplain terrains. Geologic bedrock formations from the source geologic mapsare divided into 12 categories on the derivative maps, based on age and rock type. CGS rectified inconsistenciesalong the boundaries of mapped areas to create a seamless Derivative GIS Database, but retained links to theoriginal mapping in the Source GIS Database so that the more detailed basic geologic information can beretrieved. Correlation of equivalent deposits across the whole southern California project area is representedin the GIS table entitled Correlation of Derivative and Source Geologic Map Units.
MAP UNITS
Late Holocene (Surficial Deposits)
Holocene to Late Pleistocene (Surficial Deposits)
Late to Middle Pleistocene (Surficial Deposits)
Middle to Early Pleistocene (Surficial Deposits)
Tertiary (Bedrock)
Mesozoic and Older (Bedrock)
Tertiary age formations of volcanic originTvTv
Cretaceous age formations of volcanic originKv
Fault -- Includes strike-slip, normal, reverse, oblique, and unspecified slip
Contact
A Spring
Road
SYMBOL EXPLANATION
Contacts
Stream
Reference contact -- Used to delineate geologic units that were mapped asseparate units on the original source map, but are consolidated on this map.
Granitic and other intrusive crystalline rocks of all agesgr
Very Old Alluvial Fan Deposits - moderately to well-consolidated, highly dissected boulder, cobble, gravel, sand, and silt deposits issued from a confined valley or canyonQvof
State boundary
% % % % % % % % % % % % % % % % % % Fluvial terrace scarp
[For geologic line symbols: lines are solid where location is accurate, long-dashed where location is approximate, short-dashed where location is inferred, dotted where location is concealed. Queries added where identity or existence may be questionable.]
Eolian and Dune Deposits - unconsolidated, generally well-sorted wind-blown sand; may occur as dune forms or sheet sand
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Lacustrine, Playa, and Estuarine (Paralic) Deposits - mostly unconsolidated fine-grained sand, silt, mud, and clay from fresh water (lacustrine) lakes, saline (playa) dry lakes that are periodically flooded, and estuaries; deposits may contain salt and other evaporites
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Alluvial Valley Deposits - unconsolidated clay, silt, sand, and gravel recently deposited parallel to localized stream valleys and/or spread more regionally onto alluvial flats of larger river valleys; sandy sedimentgenerally more dominant than gravelly sediment
Qa
Young Alluvial Fan Deposits - unconsolidated to slightly consolidated, undissected to slightly dissected boulder, cobble, gravel, sand, and silt deposits issued from a confined valley or canyonQyf
Young Terrace Deposits - unconsolidated to slightly consolidated, undissected to slightly dissected marine and stream terrace deposits
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Old Terrace Deposits - slightly to moderately consolidated, moderately dissected marine and stream terrace deposits!
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Old Alluvial Fan Deposits - slightly to moderately consolidated, moderately dissected boulder, cobble, gravel, sand, and silt deposits issued from a confined valley or canyonQof
Very Old Alluvial Valley Deposits - moderately to well-consolidated, highly dissected clay, silt, sand, and gravel along stream valleys and alluvial flats of larger rivers; generally uplifted and deformedQvoa
Alluvial Wash Deposits - unconsolidated sandy and gravelly sediment deposited in recently active channels of streams and rivers; may contain loose to moderately loose sand and silty sand
Projection: Universal Transverse Mercator, Zone 11 North, North American Datum of 1983.Topographic contours derived from USGS 1/3 arc-second National Elevation Dataset (NED). Shaded topographic relief derived from USGS 1 arc-second NED. Base map of hydrography from National Hydrography Dataset Plus (NHDPlus) and California Department of Fish and Game. Base map of geographic names from USGS Geographic Names Information System (GNIS).
MAP LOCATION
CALIF.
INDEX TO USGS 7.5' QUADRANGLES
SCALE 1:100 000
CONTOUR INTERVAL 50 METERSNATIONAL GEODETIC VERTICAL DATUM OF 1929
5000 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000 FEET
5 0 52.5 MILES
050005 0 5 102.5 KILOMETERS
METERS5000 10000
APPROXIMATE MEANDECLINATION, 2010
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Blythe
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ARIZONA
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Ksh
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pKm
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BlackPoint
BlackHill
HallIsland
McCoyPeak
Black Rock
Quien Sabe Point
P
al
o
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es
a
M u l e M o u n t a i n s
Little Chuckwalla Mountains
C U C K W A L L A
V A L L E Y
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UN
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I A M
OU
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AI N
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EY
Ford Dry Lake
Color
ado R
iver
McCoy Wash
Color
ado R
iver
114°5'
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114°34°34°
33°30' 114°
AREA NOTMAPPED
A R I Z O N A
AREA NOTMAPPED
Alluvial Fan Deposits - unconsolidated boulders, cobbles, gravel, sand, and silt recently deposited where a river or stream issues from a confined valley or canyon; sediment typically deposited in a fan-shaped cone; gravelly sediment generally more dominant than sandy sediment
Qf
Coarse-grained Cretaceous age formations of sedimentary originKss
Fine-grained Cretaceous age formations of sedimentary originKsh
CORRELATION OF MAP UNITS
Late Holocene
Holocene toLate Pleistocene
Late to Middle Pleistocene
Middle toEarly Pleistocene
Tertiary(Bedrock)
Mesozoic and Older (Bedrock)
AlluvialWash
DepositsAlluvial
FanDeposits
AlluvialValley
DepositsTerraceDeposits
Lacustrine, Playa, and EstuarineDeposits
Eolian and Dune Deposits
Cretaceous andPre-Cretaceous
Metamorphic(sedimentaryand volcanic)
GraniticRocks
(all ages)
Coarse-grained
Fine-grained Volcanic
Alluvial Deposits
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Quate
rnary
Surfi
cial D
epos
its
Qw
* Boundaries of Quaternary units are gradational and time transgressive in a regional sense.
*
represented on this map by 8 of the 11 project derivative bedrock units (see Map Units and Correlation of MapUnits). Quaternary surficial deposits and geologic formation names originally compiled by Stone (2006) arecorrelated with derivative categories used by CGS in the Geologic Labels GIS spreadsheet for the west half ofthe Blythe quadrangle. This map, along with others in the Geologic Compilation of Quaternary Surficial Deposits in SouthernCalifornia Derivative GIS Database, is regional in nature and should not be used as a substitute for detailedgeologic studies in any specific area. It is intended only for rapid identification of areas subject toprevious and potential future flooding and other geologic hazards on alluvial fans and floodplains.
Cretaceous and pre-Cretaceous metamorphic formations of sedimentary and volcanic originpKm
www.conservation.ca.gov/cgsThe Department of Conservation makes no warranties as to thesuitability of this product for any particular purpose.Copyright 2010 by the California Department of Conservation.All rights reserved. No part of this publication may be reproduced without written consent of the California Geological Survey.Information on this map is not sufficient to serve as a substitute for the geologic and geotechnical site investigations required under Chapters 7.5 and 7.8 of Division 2 of the California PublicResources Code.
©
Coarse-grained Tertiary age formations - primarily sandstone and conglomerateTss
Fine-grained Tertiary age formations - includes fine-grained sandstone, siltstone, mudstone, shale, siliceous and calcareous sedimentsTsh
