DISPLACEMENT HISTORY AND AFFINITY OF THE TRUCKHAVEN FAULT, IMPERIAL COUNTY CAIFORNIA – IS THIS...

DISPLACEMENT HISTORY AND AFFINITY OF THE TRUCKHAVEN FAULT, IMPERIAL

COUNTY CAIFORNIA – IS THIS FAULT PART OF THE WEST SALTON DETACHMENT

FAUT ZONE OR THE SAN JACINTO FAULT ZONE?

By

Giovanni A. Norman

Advisor: Dr. David Kimbrough

A Thesis Presented to the

FACULTY OF THE DEPARTMENT OF GEOLOGICAL SCIENCES

In Partial Fulfillment of the

Requirements for the Degree

BACHELOR OF SCIENCE

General Geology

May 2015

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ABSTRACT 4

INTRODUCTION 5

REGIONAL GEOLOGY 5

PREVIOUS WORK 6

TECTONICS 8

Truckhaven Fault Zone 8

West Salton Detachment Fault 8

Offset on the San Andreas 9

STRATIGRAPHY 11

Basement Complex 11

Canebrake Conglomerate 11

Palm Spring Formation 12

Silicified Sediments 13

Older Alluvium 14

Alluvium 14

METHODS 15

RESULTS 16

CONCLUSION 18

PROPOSED FUTURE WORK 18

REFERENCES 19

FIGURES 21

Figure 1: Fault Map for Western Salton Trough 21

Figure 2: Geologic Map of Northwestern Salton Trough 21

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Figure 3: Paleogeography of Salton Trough/Gulf of Mexico 22

Figure 4: Reorganization of the West Salton Detachment 22

Figure 5: Stratigraphy of Northwestern Salton Trough 23

Figure 6: Map of Cahuilla Gold Mine 23

Figure 7: Cahuilla Gold Mine southeast towards the Salton Sea 24

Figure 8: Truckhaven Fault 24

Figure 9: Slickenlines exposed at Truckhaven Fault 25

Figure 10: Google Earth Image showing major alteration zone 25

Figure 11: Thin Section Analysis of Amphibolite Gneiss 26

Figure 12: Reverse Fault at source of Wonderstone Wash 26

Figure 13: Seismic activity along San Jacinto Fault Zone 27

Figure 14: USGS-Caltech Recent seismic map 27

Figure 15: Map Insert 28

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ABSTRACT

The Rainbow Rock Quarry is part of the footwall of the Truckhaven Fault and has

been a gold and silver mining prospect for over one hundred years. It is situated along the

north edge of Wonderstone Wash in the northwestern Seventeen Palms USGS 7.5 minute

quadrangle, located in the southeastern section of the active San Andreas Fault system.

This region is characterized by seismic activity, continental rifting, volcanism,

hydrothermal alteration, rapid sedimentation and active precious metal deposition. The

Truckhaven Fault zone strikes ~N65°E and separates a Cretaceous quartz monzonite

footwall from Plio-Pleistocene Canebrake Conglomerateand Palm Spring Formation in the

hanging wall. Well-developed slickenlines at one locality document sinistral normal slip on

the Truckhaven Fault. The fault zone dips southeast and hosts sites of alteration mostly in

hanging wall rocks, including gold and silver mineralization and argillization. To the

southwest of Rainbow Rock is the source of Wonderstone Wash. The goal of this project

was to conduct a field investigation of the area where the Truckhaven Fault strikes into the

West Salton Detachment and determine the relationship between these two faults. Several

exposures of hydrothermal alteration were observed in this area in addition to reverse

faulting and metamorphic amphibolite rocks were studied in thin section to better

understand the rocks that may represent the footwall of the West Salton Detachment. By

illustrating the architecture of these two faults, we hope to understand the kinematics

during their activity, in order to question whether they remain active, or accommodation

has been relieved by the San Jacinto Fault system.

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INTRODUCTION

The Cahuilla Gold Mine at Rainbow Rock is a Pleistocene epithermal gold deposit

that intrudes Pliocene-Pleistocene Canebrake Conglomerateand Palm Spring Formations

(Wakefield, 2007). Adjacent to the mine to the southwest, Wonderstone Wash hosts several

exposures providing a window into Southern California’s tectonic history. The

Southeastern Santa Rosa Mountains host the trace of the northeast striking normal sinistral

Truckhaven Fault (Figure 1), which may sole into the northern segment of the West Salton

Detachment Fault, or alternatively link to and accommodate strain on the Clarke fault

segment of the San Jacinto Fault zone (Janecke, 2008). The West Salton Detachment in this

area separates Plio-Pleistocene Canebrake Conglomeratefrom lower crustal gneissic

amphibolite facies.

REGIONAL GEOLOGY

The Salton Trough is the northern extension of the Gulf of California, a rift basin

formed by strike slip motion between the North American and Pacific plates (Frost et al.,

1996). A series of short oceanic spreading ridges offset by long transform fault separates

Baja California from mainland Mexico and this system extends into the Salton Trough and

becomes the San Andreas Fault.

Sediments washing down Colorado River have been dumped into the Salton Trough,

forming a large fan shaped delta, isolating the Salton Trough region from the rest of the gulf

to the south (Frost et al., 1996).

The Santa Rosa Mountains form the prominent mountain range on the northwest

flank of the Salton Trough (Figure 2). Near Palm Springsthe roots of the Peninsular Ranges

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batholith are exposed on the northeastern edge of the regional tilt block. The Peninsular

Ranges Batholith extends from Orange County to the southern tip of Baja California. It

consist mostly of rocks of intermediate composition, primarily tonalities intruding pre-

existing metasedimentary and metavolcanic rocks (Frost et al., 1996).

PREVIOUS WORK

The Salton Trough has been widely studied over the past century. In a 1954 paper

discussing the Geology of the Imperial Valley, Dibblee described the Truckhaven Fault,

Canebrake Conglomerateand identified the Truckhaven Rhyolite as “varicolored felsitic

rock that was extruded along an adjacent east-west fault.”

In 1968 and 1979 Sharp recognized the brittle detachment faults of the Peninsular

Ranges, and spatially associated with the eastern Peninsular Ranges mylonite zone for

most of their length.

In 1968, Weismeyer mapped the northern portions of the Seventeen Palms and

Fonts point quadrangles and provided an in-depth stratigraphic, structural and geomorphic

assessment of the area, renaming Dibblee’s Rhyolite to silicified sediments.

In 1996 Frost and Robinson described the Salton Trough as having been affected by

regional detachment faulting and developing an array of normal linked faults above a

ductile middle crustal zone. Those zones of middle crustal weakness are thought to have

largely localized the different strands of the San Andreas system during the Pliocene.

In 1998 Axen and Fletcher described Late Miocene-Pleistocene extensional brittle

detachment in the Laguna Salada-Salton Trough region, synchronous with the deposition of

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the Imperial and Palm Spring Formations. They described these detachments as distinctly

younger than detachment fault to the east of the San Andreas within the Colorado River

extensional corridor which are overlapped by undeformed, age-equivalent, marine or

lacustrine rocks of the Bouse Formation.

In 2007, Belgarde and Janaeke interpreted the Truckhaven FaultFault as part of the

San Jacinto Fault system, the northern boundary of the Arroyo Salada damage zone, a

structure that links to and accommodates strain. (Belgarde, Janaeke, 2007)

Dorsey, Axen. Housen and Janecke conducted NSF-supported research to study the

timing and kinematics of West Salton Detachment Fault slip history, the resulting basin

architecture, associated sedimentation patterns and the relationship of those faults and

basins to synchronous slip on the San Andreas Fault.

TECTONICS

The modern Pacific-North American plate boundary is dominated by dextral faulting

concentrated along faults of the San Andreas system (Axen & Fletcher, 1998). This

boundary can be divided into three domains from north to south in which the strain

partitioning differs. The northern domain extends from the Mendocino triple junction to

the north side of the Transverse Ranges. The central domain includes the Transverse

Ranges and the "big bend" of the San Andreas Fault, where the fault changes strike WNW.

The northern Gulf-Salton trough region lies at the northern end of the southern domain.

Continental crust has been completely rifted apart and transitional crust, composed of

sedimentary strata, young deep in crust, mylonite gneiss form very strong rock body once

cooled (Axen & Fletcher, 1998)

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During the early to late Miocene, this region experienced continental sedimentation,

volcanism and the formation of fault-bounded nonmarine rift basins. From the Pliocene to

early Pleistocene, the region underwent extension and transtension on a system of regional

detachment faults. This resulted in the formation of large basin, with marine sedimentation

then later terrestrial sedimentation. From the Pleistocene until modern times, strike-slip

faulting and related folding in the San Jacinto and Elsinore fault zones resulted in the uplift

and erosion of older deposits. These stages are illustrated in Figure 3 (Dorsey, 2006).

Truckhaven Fault Zone

The Truckhaven Fault zone consists of the normal sinistral E-NE striking

Truckhaven Fault separating a Jurassic quartz monzonite footwall from a Tertiary

conglomerate, sandstone and silicified sediment hanging wall. Dipping south, this zone

hosts mineralization, alteration and argillization (Wakefield, 2007).

Pleistocene siliceous sinters interbed with fluvial sediments and basin-margin

conglomerate facies. NW striking strike slip faults cut through the Truckhaven Fault zone.

Mineralization occurs in clastic sediments, fanglomerates and quartz monzonite, and may

be concentrated along complex fault interactions. Mineralization includes several high

grade banded veins located within an extensive system of tabular disseminated deposits

(Wakefield, 2007).

The Truckhaven FaultFault has been designated as the northern boundary of the

Arroyo Salada damage zone (Belgarde, 2007). It has been suggested that there are also

reverse and strike slip components to the fault (Janaeke, 2008)

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West Salton Detachment Fault

Detachment faulting, also referred to as low angle normal faulting is a process of

crustal extension that was involved in the formation of the the Salton Trough.. The Western

Salton Trough detachment fault is exquisitely exposed in the Santa Rosa Mountains and

other places in the Salton Trough. Similar crustal extension occurred within much of the

southern basin and range province, Colorado River and Mojave Desert provinces (Frost et

al., 1996).

The same extensional type of faulting tilted the Peninsular Ranges over so that the

highest portion is on the easternmost, tipped portion of the Santa Rosa Mountain block and

the lowest portion on westernmost downdropped portion of the block (coastal California)

(Frost et al., 1996).

The West Salton Detachment fault is a series of low-angle normal faults that can be

traced for 180 kilometers from the Santa Rosa Mountains to the Tierra Blanca Mountains

(Dorsey, 2002). This fault was active from late Miocene to early Pleistocene (Axen &

Fletcher, 1998). It accommodated NE-SW extension in a regional strain partitioning

pattern during dextral slip on the San Andreas Fault. The detachment offsets steeper

Cretaceous Santa Rosa mylontie from the pervasively brecciated crystalline rocks in the

immediate hanging wall (Dorsey, 2002).

Offset on the San Andreas System

Since the Pleistocene, the strike slip component in this region has been predominant

and resulted in the northern portion of the West Salton Detachment along the Santa Rosa

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Mountains to become offset from traces in the San Felipe Fault Zone. The reorganization of

the West Salton Detachment can be referred to in Figure 4 (Dorsey, 2013).

The Santa Rosa Mountains compose a solid block originally formed in northern

Mexico, suffering relatively little deformation during offset along the San Andreas Fault.

The weaker crustal strength sediments to the east composing the Salton Trough record

deformation along the San Andreas Fault zone. Progressive offset is recorded in sediments

derived from the high portions of the Peninsular Ranges, as well as the Chocolate and

Orocopia Mountains (Frost et al., 1996).

STRATIGRAPHY

Weismeyer’s 1968 master’s thesis provides an in depth reference for stratigraphy in

the study area. A basement complex of quartz monzonite intruding metasediments is

overlain by Plio-Pleistocene basin margin facies interbedded with fine grained sandstones

and silicified sediments (Figure 5).

Basement Complex

The basement complex consists of metasediments dominated by dark biotite schist

interbedded light colored crystalline limestone, with minor occurrences of granitic and

garnet gneiss, quartzite and phyllite. These pre-Cretaceous metasediment country rocks

are commonly amphibolite facies, intruded by granitic bodies (Axen & Fletcher, 1998).

These granites occur as dikes, sills, small irregular bodies. These granites are light colored,

with a pegmatitic texture. The granitics to the north of the eastern Truckhaven Fault have

since been recognized as quartz monzonite (Wakefield, 2007).

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Canebrake Conglomerate

The term Canebrake Conglomeratewas first used by Dibblee (1954), and reaches its

maximum thickness at 7000 feet at Canebrake Wash, at the base of Vallecito Mountain. The

unit accumulated in braided streams and alluvial fans on the flanks of steep mountains

surrounding the delta plain of the ancestral Colorado River. The Imperial and Palm Spring

formations coarsen westward into this basin-margin facies, which in 1998 was interpreted

by Axen and Fletcher as the main-fault scarp facies of the West Salton Detachment System.

The Canebrake is divided into five subunits, Tcu, Tc4, Tc3, Tc2, Tc1. The

undifferentiated unit is a gray nonmarine, fanglomerate sandstone. Tc4 is non marine, light

gray thick bedded to massive, poorly indurated sandy fanglomerate. Tc3 is a nonmarine,

light gray to tan, moderately indurated conglomeratic sandstone with minor clay and

siltstone. Tc2 is a grey to brown, massive moderately indurated boulder fanglomerate. Tc1

is tan conglomeratic high indurated sandstone which is moderately fractures.

Of the five units of Canebrake conglomerate, Tc4 is the most widespread and

thickest. It is the principle unit in study area, up to 1000 feet in thickness. Light gray to buff

in color, it is a poorly indurated sandy conglomerate. Clasts mainly consist of pebbles and

cobbles encompassed in an unsorted arkosic micaceous arenite matrix. There is poor to

good stratification mostly delineated by alignment of clasts and micaceous layers within

the sandstone.

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Palm Spring Formation

A tan and buff, fine to coarse grained micaceous arkosic sandstone defines the

dominant lithology of the Palm Spring Formation, comprising most of the lower central

portion of the study area. Massive bedding is predominant, with common cross bedding

and thin to medium beds. Induration ranges from poor to moderate. Grains are mostly

subangular and subrounded, with quartz and feldspar the dominant minerals with minor

micas. Thin and discontinuous pebbly conglomerate stringers are common where the

formation changes facies completely to the Canebrake Conglomerate.

Light gray and buff fine grained concretionary sandstone is common, seldom greater

than 20 feet thick, yet striking in their color contrast. Various mudstone and claystone

layers are also interbedded with the sandstone. Reddish brown when weathered, fresh

surfaces yield a medium reddish brown, yellow, green buff and gray, with minor purple

beds. These mud beds mostly show a mottled texture and poor bedding. Moderate to well

indurated, they commonly break into irregular conchoidal fragments. Thickness of beds

range from less than an inch to over one hundred feet, with most beds between 10 to 15

feet thick and interbedded with fine grained sandstone lenses.

The formation is generally agreed to have been formed in a terrestrial deltaic

environment, with minor marine incursions. The material comprising the sediment was

partially derived from local sources, as the Palm Spring Formation grades laterally into the

Canebrake Conglomerate. However, the bulk of the sediment occupying the Salton trough

was imported by the Colorado River, according to Merriam and Bandy 1965. The oldest

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constraint for the age of the formation is Pliocene, due to the late Miocene to Pliocene age

of the underlying Imperial Formation.

Silicified Sediments

Adjacent to Truckhaven Fault, the youngest Canebrake Conglomerateunit is finer

grained, and grades eastward into a highly silicified sequence of sandstones, mudstones

referred to as silicified sediments. Along the Truckhaven Fault, three domains of exposures

can be described.

The westernmost exposures are only moderately silicified, far more friable than in

the east. These exposures consist of thin to medium bedded conglomerate and sandstone.

The gray arkosic sandstone beds are usually less than one foot thick, and consist primarily

of subangular to subrounded grains of quartz, feldspar and biotite, with minor zircon and

muscovite. Sand grains range from fine to coarse grained, fair to poorly bedded with

infrequent cross bedding. Generally massive conglomerate beds range from 2-15 feet thick

with clasts varying from pebble to cobble, composed of gneiss, limestone and

tonalite/quartz monzonite.

The central exposure of silicified sediments appears to be exposed at a lower

stratigraphic interval, a coarse cobble to boulder fanglomerate. Much appears to be missing

from erosion. Remnant 6 inch cobbles can be seen surrounded by alteration ring of white,

red and purple, friable siliceous material. Hot springs amorphous sinter deposits up to a

foot thick are interbedded with fanglomerate sediments.

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The eastern exposures are the most highly silicified and leached. Medium to coarse

grained, cross bedded sandstone 1-20 feet thick interbeds with hot springs amorphous

silica deposits up to 5 feet thick. Coarse pebbly sandstone beds are completely altered so

that the only grains recognizable are subrounded moderately etched quartz grains. The

matrix consists of amorphous silica, either chalcedony or opal.

These sediments were formed by the percolation of silica rich waters along the

Truckhaven Fault zone. Deposition of the youngest Canebrake is contemporaneous to the

hot springs deposits, as layers of amorphous silica are interbedded with fanglomerate. It is

suggested that these sinter deposits were deposited at the surface and later buried.

Fossilized “reed-like” structures occurring locally throughout the formation further suggest

contemporaneous deposition and silicification.

Older Alluvium

All inactive accumulations of alluvial fan deposits and stream terrace deposits are

designated older alluvium. The bulk of the sediment has been derived primarily or

secondarily from the Santa Rosa mountain basement rocks. This older alluvium consists of

tan to brown, poorly sorted, poorly compacted, locally cemented conglomerate. Pebble and

boulder clasts are angular to subrounded and consist of tonalite, schist, gneiss and

limestone. The matrix is a tan to buff, arkosic arenite matrix, with poorly sorted fine to very

coarse grains of quartz and feldspar.

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Alluvium

Alluvial material, derived mostly from the basement complex, Canebrake and older

alluvium, partially fills most Wonderstone wash. In the western, eastern flowing

intermittent streams, coarser fractions of thin, discontinuous alluvium are concentrated,

exposing barren bedrock in many places. The Palm Spring Formation is the primary source

to the south and the east, with fine grained clays, silts and sands composing the derived

alluvium.

METHODS

Mapping over the course of 4 days during early January 2015 (Figures 6, 7) covered

the eastern portion of the Truckhaven Fault zone corresponding to the Cahuilla property.

The objective was to map along the well-defined trace of the Truckhaven Fault in order to

determine if the mineralization is restricted to the hanging wall. As field assistant to Diane

Cheung-Harris, we collected samples in order to determine the age of mineralization of the

silicified sediments. It was also the goal to interpret how much slip has Truckhaven has

encountered after the mineralization.

Mapping during late March 2015 encompassed the western portion of the

Truckhaven Fault along Wonderstone Wash where the Truckhaven encounters the West

Salton Detachment Fault (Figure 15). The goal of these 3 days in the field was to

understand the nature of the Truckhaven Fault and to visit a major altered zone at this

interaction. Paul Stubbe, Vice President of Project Development, Teras Resources, assisted

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in transportation to the desolate, isolated study area. Attitudes of fault traces and slicken

lines were recorded to determine slip direction.

Thin section petrography was performed on a sample of amphibolite gneiss to draw

insight regarding the composition of the footwall of the West Salton Detachment. Regional

Earthquake history was also studied to draw insight regarding the timing of activity and

classification of the Truckhaven and the West Salton Detachment.

RESULTS

During mapping along Wonderstone Wash, several exposures of the Truckhaven

Fault were observed (Figure 8). In the east, the character of the fault is normal sinistral

(Figure 9), with extreme hydrothermal alteration and interbedded sinter deposits. The

western exposures of silicified sediments are only moderately silicified, far more friable

than those in the east (Weismeyer, 1968). Further west, fault interactions are marked by

more minor alterations of surrounding basement and conglomerate units.

At the source of Wonderstone wash, the trace of the fault can be followed again with

exposures of altered basement and Canebrake Conglomerate. A major alteration zone lies

in the locality of the interaction of the West Salton Detachment and the Truckhaven Fault.

(Figure 10) At least 6 fault traces can be seen when walking though Wonderstone Wash

with unaltered Canebrake ConglomerateTc4 to the north and south, and an large altered

zone of Canebrake north of the northern strip of unaltered conglomerate.

Exposures of amphibolite gneiss were sampled from basement lineations striking to

the northwest and dipping to the northeast. Thin section analysis (Figure 11) identified

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quartz, clinopyroxene, plagioclase and abundant amphibole. This exposure is interpreted to

be the footwall of the West Salton Detachment fault.

Southwest of the first gneiss exposures is subtle exposure of what is interpreted as a

low angle reverse fault (Figure 12). This fault strikes 51° northeast and dips the 23°

southeast. Black Gouge appears to be cut by a normal fault.

Interpretation of recent and historical earthquake maps from Cal-Tech and the Bay

Area Earthquake (Figures 13, 14) alliance display a lack of seismic activity on both the

Truckhaven Fault and the West Salton Detachment. The proximity of inactive faults to the

very active San Andreas to the North and the active San Jacinto Fault Zone infers that the

Truckhaven is part of the inactive West Salton Detachment Fault zone rather than the San

Jacinto Fault Zone.

CONCLUSION

Mapping of the Truckhaven Fault (Figure 15) shows down-to-the south normal

faulting, with slickenlines indicating oblique normal-sinistral slip. Epithermal

mineralization is restricted to the hanging wall of the Truckhaven Fault zone and

Canebrake-Palm Spring Formation rocks. The West Salton Detachment is broken up by the

Clark Fault strand of the San Jacinto Fault Zone from exposures in the San Felipe fault zone

to the south. Lack of seismic activity along the West Salton detachment fault and

Truckhaven Fault infers that the Truckhaven Fault belongs to the inactive segment of the

West Salton detachment zone, as opposed to the San Jacinto Fault zone.

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PROPOSED FUTURE WORK

Diane Cheung-Harris is currently working on determining the age and movement on

the detachment fault utilizing 40Ar/39Ar dating. She is also asking whether the

Truckhaven Rhyolite/Silicified Sediments are related to detachment fault strain

localization and mineralization. It is also proposed that the major area of alteration at the

source of Wonderstone Wash be mapped in greater detail, at a higher resolution in order to

focus dynamics regarding local interaction of multiple faults. Additional mapping and

petrography of exposures of amphibolite gneiss and mylonites further west may constrain

parameters the slip history of the detachment and better characterization of middle to

lower crust exposures.

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REFERENCES

Axen, G. J., and Fletcher, J. M., 1998, Late Miocene-Pleistocene extensional faulting, northern

Gulf of California, Mexico and Salton Trough, California. International Geology

Review, v. 40, p. 217-244.,

Bay Area Earthquake Alliance: How close to a fault do you live?

http://bayquakealliance.org/howclose/

Belgarde, B.E., 2007, Structural Characterization of Three Southeast Segments of the Clark

Fault, Salton Trough California. Utah State University MS Thesis.

Cal-Tech-USGS: Southern California Earthquake Data Center: Accessed 5/19/15

http://scedc.caltech.edu/recent/Maps/116-34.html

Dibblee, T. W., Jr., 1954, Geology of the Imperial Valley region, California: California Div.

Mines Bull. 170, Chap. 2, Contribution 2, p. 21-28

Dorsey, R. J. 2013. Late Cenozoic Evolution of the Southern San Andreas Fault System:

Insights From Stratigraphy and Basin

http://earthquake.usgs.gov/regional/nca/seminars/2013-05-29/

Dorsey, R. J., and Janecke, S. U., 2002, Late Miocene and Pleistocene West Salton

detachment fault and basin evolution, southern California: New insights: Geological

Society of America Abstracts with Programs, Vol. 34,

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Dorsey, R.J., in: Jefferson, G.T. and Lindsay, L.E. (eds.) (2006) - Stratigraphy, tectonics, and

basin evolution in the Anza-Borrego Desert region. Fossil Treasures of Anza-

Borrego Desert. Sunbelt Publications, San Diego, CA, p. 89-104.

Frost, E. G., Fattahipour, M. J., and Robinson, K. L.,1996, Neogene detachment and strike-slip

faulting in the Salton Trough region and their geometric and genetic

interrelationships, in

Janecke, S.U., and Belgarde, B.E. 2008, A "Hidden" Fault? Structural Geology of Three

Segments of the Clark Fault, San Jacinto Fault Zone, California: Fault System History

/ SoSAFE Workshop,

Wakefield, T2007. Teras Resources Inc. Cahuilla Property, Imperial County, California NI

43-101 Technical Report

Weismeyer, A.L. 1968. Geology of the northern portions of the Seventeen Palms and Fonts

Point quadrangles, Imperial and San Diego Counties, California. M. A. Thesis,

University of Southern California

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FIGURE 1: Fault Map for the Western Salton trough. Study area is outlined by the red box (Dorsey, 2013)

FIGURE 2: Geologic Map of Northwestern Salton Trough. Study area is outlined by the yellow boxes (Dorsey, University of Oregon)

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FIGURE 3: Paleogeographic Reconstruction of Salton Trough/Gulf of Mexico. The transtensional regime can be seen followed by the dominance of the dextral San Andreas Fault (Dorsey 2006)

FIGURE 4: Reorganization of the West Salton Detachment Fault. Since 1.2 mya, the West Salton Detachment has been broken up by detral movement on the San Andreas Fault. Study area encompassed by red box(Dorsey, 2013)

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FIGURE 5: Stratigraphy of Northwestern Salton Trough (Dorsey, 2006)

FIGURE 6: Geologic Map of Cahuilla Gold Mine, modified from Weismeyer (1968)

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FIGURE 7: Cahuilla Gold Mine looking southeast towards the Salton Sea. Note the unaltered wedge of Canebrake Conglomeratesurrounded by silicified sediments.

FIGURE 8: Truckhaven Fault @ N33.353974°, W-116.113652° Slickenlines shown in next figure indicate slip direction. Looking west

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FIGURE 9: Slickenline exposure indicating down-to-the south slip at Truckhaven Fault @ N33.353974°, W-116.113652°. Looking southwest

FIGURE 10: Google Earth image showing major multicolored alteration zone in Canebrake Conglomerate. Gneiss exposure denoted by star and lineation in the west

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FIGURE 11: Petrographic Analysis of Amphibolite Gneiss @ N 33.349153°, W -116.136320°

FIGURE 12: Reverse fault (orange) interpreted from drag lines at N33.347597° -116.137718°. Fault Gouge may be truncated by a normal fault (yellow). Looking south

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Figure 13: Map of historical seismic activity in regional area. The lack of earthquakes in the study area (red box) infers the Truckhaven and WSDF may be locked or inactive Image courtesy of Bay Area Earthuake Alliance: How close to a fault do you live? (www.bayquakealliance.org/howclose/)

Figure 14: USGS Caltech Recent Seismic map showing a lack of seismic activity in the study area (red box) http://scedc.caltech.edu/recent/Maps/116-34.html

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Figure 15: Map of the Truckhaven Fault modified from Weismeyer (1968)