Determining the nature of the contact between the eastern...
Transcript of Determining the nature of the contact between the eastern...
DETERMING THE NATURE OF THE CONTACT BETWEEN THE EASTERN
SIERRA NEVADA MOUNTAIN FRONT AND THE BIG PINE
VOLCANIC FIELD SOUTH OF GOODALE CREEK IN
OWENS VALLEY, CALIFORNIA
An Undergraduate Thesis
Presented to
The Faculty of
California State University, Fullerton
Department of Geological Sciences
In Partial Fulfillment
of the Requirements for the Degree
Bachelor of Science
in Geology
By
Jazmine Titular
September 2016
Dr. Phil Armstrong, Faculty Advisor
DETERMING THE NATURE OF THE CONTACT BETWEEN THE EASTERN SIERRA
NEVADA MOUNTAIN FRONT AND THE BIG PINE
VOLCANIC FIELD SOUTH OF GOODALE CREEK IN
OWENS VALLEY, CALIFORNIA
An Undergraduate Thesis
Presented to
The Faculty of
California State University, Fullerton
Department of Geological Sciences
In Partial Fulfillment
of the Requirements for the Degree
Bachelor of Science
in Geology
By
Jazmine Titular
September 2016
Dr. Phil Armstrong, Faculty Advisor
DETERMINING THE NATURE OF
THE CONTACT BETWEEN THE
EASTERN SIERRA NEVADA
MOUNTAIN FRONT AND THE
BIG PINE VOLCANIC FIELD
SOUTH OF GOODALE CREEK IN
OWENS VALLEY, CALIFORNIA
Jazmine Titular Bachelors of Science in Geology California State University, Fullerton Undergraduate Thesis, September 2016 Advisor: Dr. Phil Armstrong
Acknowledgements
This 21 month journey and experience would not have been possible without the support of the following
people:
Dr. Phil Armstrong – Thank you for the continual motivation and guidance that helped me stay focused
and determined throughout this project. You have not only taught me how to be successful when it comes
to conducting field work and research, but you also have shown me the importance of being flexible in
times when things go differently than planned. Working with you during my last semesters at CSUF has
given me confidence that I will be successful wherever I attend graduate school, and I could never thank
you enough for helping me solidify my confidence. I hope to make you proud as I continue on my
educational journey and future career.
Amanda Shellhorn – This project would not have been possible without all your help and encouragement
throughout the months. I could not picture wandering around cinder cones in 45°F weather and 50 mph
gusts in the eastern Sierra Nevadas with anyone but you. You have shown me the importance of working
with someone who challenges me on an intellectual level as well as empathizes with me when the stress
of research feels unbearable. Thank you for being by my side for countless hours in front of computers,
working on presentations, hiking cinder cones, and camping all alone in Owens Valley – those hours will
never be taken for granted, or forgotten!
My family – Mom, Dad, and Josh – Thank you for continuously showing support and love from the late
nights spent in front of my lap top, to the continuous weekends I was not home while conducting field
work. You all made sure that I would avoid overworking by stepping in and making sure I would take
care of myself, but would also remind me to stay on top of my projects when I found little motivation. It
has been a long journey for me to earn my B.S., and this is the final project that will make all this time
and effort worth it. Thank you for everything you have and will continue to do for me, I love you!
Dr. Nicole Bonuso – During all my times of stress and frustration, you were always there to make me
laugh, smile, and help me find myself back on track. I’m thankful for conducting research with you prior
to attending CSUF – it established my skillset and understanding of how to properly approach a research
project. You taught me many mindsets to carry while doing field work, writing, and learning how to deal
with the unexepected, and I could never thank you enough for that.
Louis Stokes Alliance for Minority Participation (LSAMP) – Thank you for funding me to conduct field
work and research via the NSF grant #HRD-1302873.
Natural Sciences and Mathematics Inter-Club Council (NSM-ICC) – Thank you for providing funding to
allow me to present my research at the GSA Cordilleran Section Meeting in Ontario, CA in April 2016.
Bob Shellhorn – Your company on one of our fieldwork weekends helped Amanda and me feel more
comfortable working in the field, and gave us insight as to how to approach our research. Thanks for
being and extra set of safety eyes!
Greg Shagam, Garret Mottle, and Brian Gadbois – Your previous work laid a foundation for me to follow
as I conducted my own research. Thanks for doing such great research for me to reference!
Fred Philips – Thank you for allowing the use of your plane-fitting analysis program.
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Determining the Nature of the Contact Between the Eastern Sierra Nevada Mountain
Front and the Big Pine Volcanic Field South of Goodale Creek in Owens Valley, California
Jazmine Titular
Bachelors of Science in Geology
Undergraduate Thesis, August 2016
Advisor: Dr. Phil Armstrong
1. Abstract
The Sierra Nevada Frontal Fault Zone (SNFFZ) located along the western boundary of
Owens Valley is comprised of numerous Quaternary normal faults. These faults generally are
assumed to dip 60° and long-term extension rates for Owens Valley are calculated assuming
these steep dips. Recent studies conducted south in the Independence and Lone Pine areas of
Owens Valley and farther north in the Bishop area show shallow dips of 21-35°. These shallow
dips affect long-term extension rate calculations and the kinematic history of Owens Valley.
Quaternary Big Pine Volcanic Field (BPVF) basalt deposits that crop out along the mountain
front offer an opportunity to evaluate potential SNFFZ fault orientations in this area. This study
analyzes the contact between the mostly granitic rocks of the Sierra Nevada Mountains and the
BPVF in the vicinity of Aberdeen from just south of Sawmill Creek and north to Goodale Creek.
Working hypotheses for this contact include: (1) it is a depositional contact along the mountain
front and (2) it is a fault contact. These hypotheses were tested by mapping the contact and
surrounding rocks in detail. The contact was divided into four segments for easier analysis and
GPS locations of the contact were taken where the contact is clear. In general, the basalt-granite
contact trends NNW, however north of Sawmill Creek the contact steps west consistent with the
mountain front and the faults of the SNFFZ. Locally, especially south of Sawmill Creek, the
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basalt deposits are present on ridges with granitic basement in the intervening valleys so that the
contact V’s to show an eastward dip, consistent with east-dipping fault contact. In other areas the
contact is diffuse with thin scoria deposits located uphill from the presumed location of the
frontal fault. The mapping was correlated to detailed Google Earth images to better define the
relationships between basalt exposure and fault locations. Where the contact can be clearly
defined, plane-fitting analysis using GPS- and Google Earth-derived x, y, z locations were used
to refine potential fault orientations. Plane-fitting analysis resulted in dips ranging from 23-27°E.
This work will lead to a better understanding of the relationships between the BPV distribution
and SNFFZ faults and may help constrain the SNFFZ orientation for kinematic analysis.
2. Introduction
Understanding basic structural and tectonic processes rely on accurate estimates of
physical properties of faults, such as fault dips. Based on Anderson’s Theory of Faulting
(Anderson, 1951), normal faults generally are assumed to dip 60°; this dip is used to calculate
and understand displacement magnitude, displacement timing, slip rates, extension rates, and
uplift rates. The Sierra Nevada Frontal Fault Zone (SNFFZ) is located along the western margin
of the Basin and Range Province between the eastern Sierra Nevada Mountains and Owens
Valley (Figure 1). Previous studies along the SNFFZ determined extension rates using the
assumed dip of 60° for normal faults (e.g., Le et al., 2007). More recent studies along the SNFFZ
from Lone Pine to north of Bishop (Figure 1) show that the SNFFZ has dips between 21-35°.
Philips and Majkowski (2011) measured multiple fault planes to the north in the Bishop area
which resulted in dips ranging from 25-35° (Figure 2). Previous thesis students analyzed fault
outcrop patterns to the south in areas stretching from Independence to Lone Pine and measured
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Figure 1. General location of the Sierra Nevada Frontal Fault Zone (SNFFZ) at western
edge of the Basin and Range Province and between the eastern Sierra Nevada
Mountains and western Owens Valley. Red box highlights specific location of the
SNFFZ between Big Pine and Lone Pine. Figure adapted from Le et al. (2007).
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Figure 2. Locations
of previous studies
conducted along the
Sierra Nevada
Frontal Fault Zone
(SNFFZ) as well as
current study areas.
To the north in
Bishop, Phillips and
Majkowski (2011)
calculated dips
ranging from 25-35°.
To the south,
stretching from
Independence to
Lone Pine, previous
thesis students
analyzed fault
locations and
calculated dips
ranging from 23-52°
(Shagam, 2012;
Gadbois, 2013;
Mottle, 2014). This
research focuses on
the area highlighted
in purple, to the west
of Aberdeen.
Shellhorn (2016)
evaluated the
mountain front-Big
Pine Volcanic Field
(BPVF) contact in
the area highlighted
in pink.
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dips ranging from 25-35° (Figure 2) (Shagam, 2012; Gadbois, 2013; Mottle, 2014). If these
shallow dips are consistent along the entirety of the SNFFZ, they can increase the horizontal
displacement rates of the basin by as much as a factor of four (Philips and Majkowski, 2011).
To the west of Aberdeen, basaltic scoria deposits and cinder cones of the Big Pine
Volcanic Field (BPVF) are in direct contact with the eastern Sierra Nevada Mountain front
(Figure 3). Volcanic vents can be found along the mountain front and lava flows are observed
flowing into Owens Valley. This study aims to evaluate the contact between the SNFFZ and the
BPVF in the area between Sawmill Creek and Goodale Creek (Figure 3) in hopes of determining
the nature of the contact (Figure 4). If this contact is a fault, it will provide new fault dip data
that can be compared to previous work conducted to the north and south. The contact was
evaluated via: (1) Google Earth analysis; (2) basic mapping of air photos with GPS waypoint
analysis; (3) and contact evaluation/plane fitting analysis to determine contact orientation.
3. Geologic Background
3.1 Owens Valley
Owens Valley bounds the eastern side of the Sierra Nevada Mountains, in east-central
California. This area defines the western margin of the Basin and Range Province and the eastern
Sierra Nevada Range. Owens Valley is a graben, approximately 140 km long and 25-10 km
wide, surrounded by SNFFZ to the west and the White and Inyo Mountains to the east (Figure 1)
(Phillips and Majkowski, 2011). The SNFFZ extends approximately 600 km from the Garlock
fault to the Cascade Range (Le et al., 2007). The eastern edge of the Sierra Nevada Range has a
steep escarpment with total relief ranging from 1700 – 2700 m, while the western edge of the
White and Inyo Mountains rise more gently and only reach heights ranging from 1500 – 1000 m.
However, in the northernmost areas of the White Mountains, relief reaches up 2700 m (Phillips
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Figure 3. Locations
of Big Pine Volcanic
Field (BPFV) basalt
deposits within
Owens Valley. Red
box highlights area
of BPVF being
analyzed in relation
to the eastern Sierra
Nevada mountain
front for this study.
Figure adapted from
Vazquez and
Woolford (2015).
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Figu
re 4
.a
Figu
re 4
.b
Fig
ure
4.
(a)
Wes
twar
d v
iew
of
stu
dy a
rea
fro
m
Hig
hw
ay 3
95.
Bas
alts
of
the
Big
Pin
e V
olc
anic
Fie
ld (
BP
VF
) ca
n b
e o
bse
rved
in
dir
ect
con
tact
wit
h
the
gra
nit
e al
ong t
he
mo
un
tain
fro
nt.
Cre
ek
loca
tio
ns
iden
tifi
ed f
or
com
par
ison t
o a
eria
l vie
w.
Road
and w
ood
en p
ost
s in
fo
regro
un
d f
or
scal
e. (
b)
Aer
ial
vie
w o
f st
udy a
rea
for
a bet
ter
un
der
stan
din
g
of
the
conta
ct r
elat
ionsh
ips
bet
wee
n t
he
gra
nit
e an
d
bas
alt.
Cre
ek l
oca
tions
iden
tifi
ed f
or
spat
ial
conte
xt
and r
efer
ence
.
8
and Majkowski, 2011). The Owens Valley fault zone strikes through the axis of the valley and is
mostly a right-lateral strike-slip fault that displaces alluvial and lacustrine deposits (Bierman et
al., 1991).
3.1.1 Formation of Sierra Nevada Mountains – Owens Valley System
The Sierra Nevada Mountains began to form after development of the Cretaceous Sierra
Nevada magmatic arc, which was active while a large pulse of erosion as well as rock and
surface uplift occurred approximately 99 Ma. High erosion rates continued until approximately
52 Ma, about 25 Ma after magmatism ceased from the arc (Wakabayashi and Sawyer, 2001).
Uplift began in the southern Sierra and moved northward, with the latest uplift starting with the
migration of the Mendocino triple junction occurring approximately 4.5 Ma (Bierman et al.,
1991). Extension of the Basin and Range Province began around 35 Ma, ranging from the
northernmost Sierra Nevada Range all the way to the southern Sierra Nevada by approximately
20 Ma. Late Cenozoic uplift and east-down frontal faulting of the Sierra Nevada began around 5
Ma. This occurred at or a few million years after an increase in the dextral component motion of
the Sierra Nevada microplate relative to the stable North American plate, and after the change in
motion between the Pacific and North American plate (Wakabayashi and Sawyer, 2001). The
change of motion between these two plates led to the development of the right lateral transform
San Andreas Fault. This also caused the formation of the SNNFZ as well as the Owens Valley
fault zone due to the redistribution of stress between the two plates.
3.1.2 Lithology
Owens Valley is underlain by Cenozoic alluvium and volcanic rocks, which are underlain by
Mesozoic granitic rocks and Paleozoic sedimentary rocks. The Paleozoic sedimentary rocks
range in age from Early Cambrian to Permian with an overall thickness of approximately 4,900
meters. During the Mesozoic, these rocks were intruded and contact metamorphosed by granitic
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plutons. Basalt flows from the late Cenozoic extend from the eastern margin of the Sierra
Nevada Mountains to the west (Ross, 1965). The Big Pine Volcanic field is found within Owens
Valley and abuts the base of the eastern Sierra Nevada Mountains with basalt flows and cones
ranging in age from 130 ka - <300 ka (Bierman at al., 1991), more specifically 17 – 62 ka in
areas west of Aberdeen (Vazquez and Woolford, 2015).
3.1.3 Extension and Faulting
The San Andreas fault system is described as the boundary between the Pacific plate and
the Sierran microplate. The Sierran microplate moves approximately 12 mm/yr N36° ± 3°W
relative to the North American Plate (Argus and Gordon, 1991). Recent plate reconstruction
suggests that the Pacific plate motion relative to North America changed to a convergent
direction around 8 to 6 Ma, with the Sierran microplate changing motion relative to North
America at the same time. This suggests that the motion change affected the Great Basin
extension during this time as well (Argus and Gordon, 1991).
Owens Valley is located within the Eastern California Shear Zone (ECSZ), which
extends from Nevada to southern California and accommodates a large component of the Pacific
and North American plate motion since the late Miocene. The strain from the motion is spread
throughout the San Andreas fault system and neighboring fault systems. Quaternary faults can be
found along the Sierra Nevada range front. The western edge of Owens Valley displays fault
scarps indicating late Pleistocene and active faulting (Slemmons et al., 2008).
The ECSZ is a dextral shear zone with a NNW strike (Beanland and Clark, 1992). This
zone contains many fault systems including the White Mountains, Fish Lake Valley, Furnace
Creek-Death Valley, Hunter Mountain, Pananmint Valley, Owens Valley, and Sierra Nevada
Frontal fault zones (Figure 1). The normal SNFFZ and the dextral Owens Valley fault zone
(OVFZ) comprise the western boundary of the ECSZ as well as the Basin and Range Province
10
(Le et al., 2007). The kinematics of the ECSZ include EW extension, perpendicular to the NNW
trending fault systems within it. The ECSZ is a result of the Sierran microplate moving parallel
and perpendicular to the Pacific-North American plate boundary (Le et al., 2007).
The eastern margin of the SNFFZ displays a NNW striking mountain front with multiple
west stepping segments (Le et al., 2007). The OVFZ stretches from Owens Lake to the Poverty
Hills, where it then steps 3 km to the west, and continues north to Big Pine (Beanland and Clark,
1992). It is a 120 km long dextral strike slip fault and 3 km wide, striking N17W (Beanland and
Clark, 1992). Approximately 1 to 3 mm/yr of slip occurs along the OVFZ and trends down the
center of Owens Valley and is the result of regional scale extensions along the western margin of
the Basin and Range (Phillips and Majkowski, 2011).
3.2 Big Pine Volcanic Field
Approximately 500 km2 of Owens Valley is covered by the BPVF pyroclastics and
basalts, with the western edge coming into contact with the eastern mountain front of the Sierra
Nevada Mountains (Vazquez and Woolford, 2015). A majority of the volcanic vents of the
BPVF are found along this contact, trending in the same orientation as the mountain front and
the SNFFZ (Figure 5) (Vazquez and Woolford, 2015). Vazquez and Woolford (2015) described
these vents along the mountain front as poorly developed scoria cone displaced by Pleistocene
and Holocene faulting, and observed the pyroclastic flows deposits found only near the vents.
The youngest flows are in this study area, found between Taboose and Division Creeks, flowing
from the vents along the mountain front and down into Owens Valley (Vazquez and Woolford,
2015).
The composition of the BPVF lavas range from olivine thloeiite to alkali olivine basalt
(Vazquez and Woolford, 2015). The basalt compositions suggest they were generated at shallow
mantle depths ranging from 45 – 70 km, which could be the result of the kinematics that
11
Fig
ure
5.
Gen
eral
geo
logic
map
ad
apte
d f
rom
Vaz
quez
and W
oolf
ord
(2015).
Red
box h
ighli
ghts
area
of
Big
Pin
e V
olc
anic
Fie
ld (
BP
VF
) lo
cate
d w
ithin
stu
dy a
rea
(only
the
nort
her
n 2
/3 o
f st
udy
area
wit
hin
this
map
). V
olc
anic
ven
ts a
re m
arked
by a
ster
isks
and f
ound a
long t
he
mounta
in f
ront
in a
sim
ilar
ori
enta
tion a
s th
e S
ierr
a N
evad
a F
ron
tal
Fau
lt Z
on
e (S
NF
FZ
).
12
occurred with the uplift of the Sierra Nevada Mountains (Vazquez and Woolford, 2015).
Previous studies dated the BPFV as Pleistocene in age, placing the youngest eruptions at ~12 –
126 ka. Recent geochemical dating of the basalts show ages ranging from 17 ka – 1.2 ma, with
the basalts near Aberdeen ranging in ages of 17 – 62 ka (Vazquez and Woolford, 2015).
4. Methods
4.1 Data Collection
Prior to field work, reconnaissance was conducted using Google Earth. This allowed for
general planning and analysis of contact locations, elevation comparisons, and access points by
roads for data collection. The approximate 6 km of contact analyzed was divided into four
segments to allow for easier analysis of the contact (Figure 6). These sections were named based
on their location relative to Sawmill Creek: South of Sawmill Creek (SSC), North of Sawmill
Creek 1 (NSC1), North of Sawmill Creek 2 (NSC2), and North of Sawmill Creek 3 (NSC3). A
handheld GPS unit was used to obtain location data along the four segments of the contact. GPS
points were taken approximately every five meters to allow for high resolution measurements to
be analyzed later, along with detailed notes regarding contact characteristics. A general geologic
map of the study area was also drafted using standard mapping techniques while completing field
work, with areas farther west into the Sierra Nevada Mountains interpreted from other geologic
maps.
4.2 Google Earth Analysis
GPS data was collected using the NAD83 datum and then converted into longitude and
latitude using Earth Point. These data were imported into Google Earth to show paths of data
collection, allowed for the checking of accuracy, and provided elevation data. Google Earth also
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Figure 6. Overall contact broken into four segments for higher resolution analysis. Red lines
show boundaries of all four areas. Paths of data collection shown in green, light blue, purple,
and yellow. Documented USGS (web) faults overlain onto image to show relationship with
contact paths.
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allowed for more detailed analysis of the contact and observations for potential evidence of
faulting because of aerial viewpoints.
4.3 Contact Dip Analysis
Longitude, latitude, and elevation data were imported into an Excel planar modeling
program created by Fred Phillips (Fred Phillips, personal communication) in order to evaluate
contact dip in the four measured segments. The program allows the user to iteratively adjust
strike of a plane to find the best-fit plane through all the x, y, and z data points along the contact.
5. Results
A geologic map was constructed during data collection showing contact relationships
between the granite of the Sierra Nevada Mountains and the BPVF with overlays of documented
USGS faults (USGS, web) (Figure 7). The contact between the granitic rocks of the Sierra
Nevada Mountains and the basalt of the BPVF follows a general N-NW orientation, with a
westward step between NSC2 and NSC3. This step is consistent with the orientation of the
SNFFZ and range front (Figure 7). No basalt was observed in the area of the westward step
along the mountain front, consistent with previous work involving evaluation of basalt locations
in the area (Vazquez and Woolford, 2015).
5.1 South of Sawmill Creek - SSC
From a distance, the contact between the granite and basalt appears to be clear and
defined, with apparent volcanic vents observed (Figure 8). Although the granite is light tan, it is
still distinguishable from the darker brown scoria. The contact is not distinct, but is diffuse at
scales of a couple meters. Side views of the area show the contact dips ~30° (Figure 9). No large
boulders of basalt were observed in this area, only dark gray and black scoria with granitic float
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Figure 7. A general geologic map constructed using standard mapping techniques while collecting GPS data
along contact of interest. USGS (web) faults, key features, and interpretations overlain on map to provide an
overall interpreted understanding of study area.
16
Figure 8. Northwest/westward view of South of Sawmill Creek (SSC) to show relationship of contact between
granite and basalt. The three lobes display a defined contact expressed topographically consistent with a
dipping planar feature. Metal posts in foreground for scale.
17
Figure 9. Northward view of the middle lobe of South of Sawmill Creek (SSC). Contact is diffuse and harder
to observe up close, but the contact appears to be dipping approximately 30°E.
18
mixed in. The contact was chosen as the location where basalt fraction dominates the granite
float fraction.
The contact strikes northwest, consistent with the mountain front orientation (Figure 7).
It has a best-fit strike and dip of N10W, 23°E (Figure 10). The three lobes of this section reflect
consistent changes in elevation associated with a dip of 23°E. This calculated dip is 7° shallower
compared to the estimated 30°E dip observed in the field (Figure 9). The best-fit slope shows an
excellent fit (R2=0.95) to the GPS data. The best-fit line is dominated by the four easternmost
points on the bottom graph of Figure 10, and removal of these points would result in a slightly
steeper dip. This steeper dip could be measured approximately 30°, similar to the dip observed in
the field.
5.2 North of Sawmill Creek 1 - NSC 1
This segment is the only location where large basaltic and granitic boulders are found in
contact with each other (Figure 11). Unfortunately, the actual contact between the two rock
types is not observable. The topography in this location is steeper compared to SSC, but the
contact appears to be dipping approximately 35°. This contact is much more defined and sharp,
but transitions into a salt and pepper diffuse contact as the contact continues northward (Figure
12). The basalt boulders are dark brown, with some boulders displaying crystals of olivine and
iddingsite. The scoria includes clasts ranging from dark gray, black, brown, to red.
Similar to SSC, this segment appears to have a N-NW map pattern based on Google
Earth analysis and the field mapping. However, when x, y, and z data were imported into the
plane modeling program, the best-fit strike does not match up with the observed map pattern
probably due to the 3-D nature of the contact as it crosses hills and valleys (Figure 13). Unlike
SSC, the analysis shows a best-fit strike and dip of N6E, 19°E. A majority of the points on the
lower graph of Figure 13 are equal distances away from the best-fit line. Even if the easternmost
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Figure 10. Best-fit strike and dip orientations calculated using a planar
modeling program. The N10W strike and 23°E dip is consistent with field
observations.
20
Figure 11. Northward view of North of Sawmill Creek 1 (NSC1) displaying the sharp contact between the granite
and basalt. This is the only location where basalt boulders are observed, and actual granite/basalt contact is not
observed due to cover by boulders that have fallen from upslope. Bushes near/along contact approximately 0.5 m in
height for scale.
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Figure 12. View facing north of North of Sawmill Creek 1 (NSC1) showing the gradational change from a sharp
contact to a diffuse one moving from south to north. Brown spring of trees and bushes in foreground for scale
22
Figure 13. Best-fit strike and dip orientations calculated using a planar
modeling program. The N6E strike is inconsistent with observations in the field
and appears to trend sub-perpendicular to the mountain front.
23
cluster of points were removed from the graph, the best-fit line would remain relatively the same
dip. This calculated strike is sub-perpendicular to the observed contact direction as well as the
mountain front. The contact begins in the river drainage of Sawmill Creek and has a general
northwest trend in the southern section, similar to SSC, but sharply steps west towards the north.
This sharp westward step is inconsistent with the mountain front, which continues in a northwest
orientation. The northernmost section of this segment near the drainage has a hairpin turn back
towards the east. This segment also reflects a consistent scatter pattern along the best-fit slope
line when comparing distance along dip direction and elevation. This could be a result of not
mapping the true contact, which could be affected by the granitic float creating a false contact.
5.3 North of Sawmill Creek 2 - NSC2
Google Earth observation suggest the contact has a north-south orientation, diverging
from the westward step of the mountain front. Views from lower elevation towards this segment
show the contact out of view (Figure 14). This is due to the depression that can observed from
higher elevation on top of the cinder cone. The diffuse contact of the northern NSC1 segment
continues into the southern section of the NSC2 contact. The northern half of the section, found
at the edge of the depression mentioned, returns back to a very sharp and defined contact. The
scoria in this segment is much redder, and still lacks boulders of basalt. However, a wash of
granitic boulders can be observed spreading from the depression to the top of the cinder cone
(Figure 15). The depression itself is filled with a mixture of scoria and granite, granite being the
dominant rock type, resulting in the lighter color of sediments.
Plane modeling analysis showed a best-fit strike and dip orientation of N46W, 16°E.
Similar to NSC1, the modeling of NSC2 results in a strike that appears to be incorrect when
compared to the measured contact (Figure 16). The resulting strike does, however, match with
the expected strike that supports the westward step of the mountain front and is also consistent
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Figure 14. West facing view of North of Sawmill Creek 2 (NSC2) showing the contact gradually going out of sight
due to a depression located behind the cinder cone. Darker red scoria is observed towards to peak/volcanic vent of
the cinder cone. Bushes in foreground approximately 0.5 m in height for scale.
25
Figure 15. East facing view of North of Sawmill Creek 2 (NSC2) showing the previously mentioned depression
located between the cinder cone and mountain front. Depression is filled with granitic float and granitic boulders can
be seen stretching from the depression to the peak of the cinder cone. Granitic float within the depression makes
actual contact difficult to locate. Bushes in foreground approximately 0.5 m in height for scale.
26
Figure 16. Best-fit strike and dip orientations calculated using a planar
modeling program. The N46E strike is inconsistent with observations in
the field, but is similar to the contact orientation observed and
calculated for SSC. This segment produced the lowest amount of point
scatter in the lower graph.
27
with the two previously analyzed segments. The southern portion of this segment begins just
north of NSC1 on the north side of the drainage, and initially reflects expected elevation change
with respect to local topography. It steps to the west, then returns to the east over the first hill,
then continues in a general north-south trend towards the north. A small step to the west and
return to the east occurs in the upper third of the section, with the northern most area showing a
southwest step and northeast return. This segment surprisingly had the highest R2 value of 0.988
when compared to all other segments. The inconsistency between the mapped contact and the
suggested best-fit strike and dip could be a result of the previously mentioned depression lying
between the cinder cone and the mountain front. The depression is filled with granitic float,
which could be creating a false contact.
5.4 North of Sawmill Creek 3 - NSC3
The northernmost of the four segments displays volcanic vents right up against the
mountain front (Figure 17). These volcanic vents appear to be well preserved and have large
basalt flows that extend eastward to Highway 395. These flows appear to be the youngest in the
BPVF (Vazquez and Woolford, 2015). The flows have large basalt boulders and also exhibit
pahoehoe and aa textures. The cones are surrounded locally by pyroclastic particles and are
black, dark gray, red, and brown. The contact between the granite and basalt is sharp and easily
observable, and side views also display dips that appear approximately 35°E (Figure 18).
Consistent with SSC and NSC1, this segment exhibits a contact orientation that trends
northwest. Similar to SSC, the contact follows the elevation patterns of the two large basalt
lobes. The contact has a consistent west stepping, east returning pattern throughout the segment.
At the northernmost part of the segment, the contact diffuses into a northwest trending linear
contact where it ends at Goodale Creek. Plane modeling data supports this orientation, providing
a best-fit strike and dip of N30W, 27°E. The calculated dip is 8° shallower compared to the 35°E
28
Figure 17. View of North of Sawmill Creek 3 (NSC3) facing west displaying volcanic vents and cinder cones in
contact with the mountain front. These volcanic vents are higher in elevation compared to the lower three segments.
Volcanic vents are preserved and visible from a distance.
Vents
29
Figure 18. Northwest/northward view of North of Sawmill Creek 3 (NSC3) showing the sharp contact
between the granite and basalt. A well preserved volcanic vent can be seen and appears to create the
contact with the mountain front.
Contact between BPVF
and mountain front
Contact between BPVF
and mountain front
30
dip observed in the field. The strike appears to match up almost perfectly with the contact
measured, but results in a lowest R2 value (0.61) of all the segments (Figure 19). If the
easternmost plots of the bottom graph in Figure 19 were removed, the resulting dip would be
slightly shallower than the 27°E dip calculated. The distance along dip direction versus elevation
shows a large amount of scatter among the plotted point. Explanation for this scatter is probably
due to the poor exposure of contact areas due to granitic float from above the cinder cone vents.
6. Interpretations and Discussion
6.1 Segment Contact Interpretations
Based on relationships with mapped segments of the contact, plane fitting of the contact
locations, and Google Earth analysis, three segments have been interpreted as fault contacts:
SSC, NSC1, and NSC3. The contact along SSC is along strike of the mountain front fault as
delineated by geomorphology and springs, but bifurcates to the south (Figure 20). Preliminary
plane modeling analysis of this bifurcated fault reflects the same dip as SSC and a similar strike
orientation (Figure 21). Because the strike and dip orientation of NSC1 (N6E, 19°E) is similar to
SSC (N10W, 23°) it is logical to interpret this contact as a continuation of the fault observed to
SSC. The relatively low dip of 16°E and divergence from the mountain front suggests that NSC2
is least likely of all segments to be a fault but instead a depositional contact. Because of the
diffuse contact in the northern section of NSC2 and the large amount of granitic float in this area,
this segment can potentially be interpreted as a fault if more data are collected and analyzed. The
contact within this area could also be deformed as a result of the westward step of the mountain
front. Although NSC3 has the lowest R2 value of all the measured segments, it is still interpreted
as a fault due to clear juxtaposition of the basalt against the mountain front and the consistency
31
Figure 19. Best-fit strike and dip orientations calculated using a
planar modeling program. The N30E strike is consistent with
observations in the field, we well as calculated orientations for
South of Sawmill Creek (SSC) and North of Sawmill Creek 1
(NSC1).
32
Figure 20. Geomorphological interpretations of South of Sawmill Creek (SSC) based on the presence of
springs and geomorphic expression observed above the mapped contact. Main contact appears to bifurcate to
the south near SSC. USGS (USGS, web) faults overlain on Google Earth (blue lines) and show consistent
locations between interpretations and known faults.
33
Figure 21. Best-fit strike and dip orientations of fault mapped
from geomorphic features on Figure 20 calculated using a planar
modeling program. The calculated 23°E dip matches the
calculated dip of South of Sawmill Creek (SSC), and its N26W
strike is similar to the N10W strike of SSC. This further
supports the idea of a bifurcating fault towards the south of SSC.
34
of the contact orientation (N30W, 27°E), which is consistent with measurements from SSC and
NSC1.
6.2 Overall Contact Interpretation
The preferred interpretation for most of the continuous contact in this study area is a
fault. This is supported by the contact orientations ranging from north to northwest in strike and
approximately 20-27°E in dip, which is consistent with fault orientations to the north and south
of Aberdeen. North of NSC2, the main fault steps west, consistent with the westward step of the
mountain front and distribution of the BPVF. Documented faults (USGS, web) also step west
with the mountain front in this same area. Geomorphological observations south of SSC support
the concept of a fault along the mountain front, potentially bifurcating south and continuing
along towards faults analyzed by past thesis students. Immediately north of this study area (still
within Aberdeen), Shellhorn (2016) also analyzed the contact of the BPVF with the Sierra
Nevada Mountain front using the same methods. Data from Shellhorn (2016) reflect a range of
dips from 28 to 35°E, with an average dip of 33°E, which supports the interpretation of the
contact being a fault. Shellhorn (2016) compared the average dip of the contact to the slope of
the Sierra Nevada Mountain front by analyzing multiple elevation profiles in areas directly north
of her study area. The average contact dip is 33°E, but average slope angle is 22°E for typical
mountain front slopes (Figure 22). The discrepancy between typical mountain front slopes and
contact dips (11°) suggests the basalt was not deposited on the mountain front, but rather is a
fault contact. Thus it is logical that the mapped contact between the Sierra Nevada Mountain
front and BPVF farther south in my field area is best interpreted as a fault as well.
The alternate interpretation for this data is that all four segments are depositional and
form buttress unconformities along the Sierra Nevada mountain front. This interpretation is not
favored due to (1) the orientation of the contact between the Sierra Nevada Mountain front and
35
Fig
ure
22
. C
om
par
iso
n o
f av
erag
e S
ierr
a N
evad
a M
ounta
in f
ront
slope
angle
and a
ver
age
con
tact
dip
fro
m S
hel
lho
rn (
20
16
). A
nal
ysi
s in
cludes
mult
iple
ele
vat
ion p
rofi
les
along t
he
mounta
in f
ront.
Th
e
aver
age
slope
is 2
2°E
and t
he
aver
age
dip
of
the
conta
ct i
s 3
3°E
far
ther
no
rth
(S
hel
lho
rn, 2016).
Dis
tan
ce (
m)
36
the BPVF having the same orientations as measured contact orientations along the mountain
front in areas north and south of study area and (2) the dip of the contacts are steeper than the
typical mountain front erosional slope angle.
6.3 Discussion
Dips of 60° are currently used for normal fault kinematic analyses. Previous work
conducted in areas along the east dipping normal faults of the SNFFZ to the north and south of
Aberdeen have dips shallower than 60°. These shallow dips directly affect calculations of
displacement magnitude, displacement timing, slip rates, extension rates, and uplift rates, which
directly affects our understanding of Owens Valley kinematics. Calculated dips for this area are
consistent with shallow dips from previous studies to the north and south (Figure 23). To the
north in Bishop, Phillips and Majkowski (2008) calculated dips ranging from 25-35°E. Just south
of Bishop in Aberdeen between Taboose and Goodale Creek, Shellhorn (2016) calculated dips
ranging from 28-35°E. This study calculated dips in an area directly south of Shellhorn between
Goodale and Sawmill Creek, resulting in a range from 23-27°E. South of this area near
Independence at Shepard and Independence Creek, Shagam (2012) calculated dips ranging from
29-34°E. To the south in the vicinity of Manzanar near Bair Creek, Mottle (2014) calculated dips
ranging from 21-23°E. In the most southern area near Tuttle Creek in Lone Pine, Gadbois (2013)
calculated dips of 35°E. Data from this study is consistent with the shallow dips found in
neighboring areas and fills in the hole of missing data between Bishop and Independence. This
consistency of shallow dips stretching from Bishop to Lone Pine could help provide further
insight into the kinematic relationship between the Sierra Nevada Mountains and the BPVF
along the western margin of the Basin and Range Province.
37
Figure 23. Locations of all
studies conducted
along the SNFFZ.
To the north in
Bishop, Phillips and
Majkowski (20011)
calculated dips
ranging from 25-35°.
North of this study
area, Shellhorn
(2016) calculated
dips of 28-35°. This
study area has
calculated dips from
23-27°. To the
south, stretching
from Independence
to Lone Pine,
previous thesis
students analyzed
fault scarps and
calculated dips
ranging from 23-35°
(Shagam, 2012;
Gadbois, 2013;
Mottle, 2014).
38
6.4 Future Work
Lack of basalt at higher elevations would support the interpretation of the contact being a
fault. Basalt boulders were observed farther up Sawmill Creek Canyon, and mapping of this basalt
could help further interpret the nature of this contact. Google Earth analysis suggests a more
detailed contact analysis of NSC2 is necessary for better understanding of this segment. This is
based on observations of geomorphologic changes that occur along the mountain front at higher
elevations where the westward step occurs. Areas north of Aberdeen show two locations that
appear to be small dark flat areas compared to the surrounding lighter granite at higher elevations
compared to this study: (1) Stecker Flat; north of Taboose Creek and (2) Shingle Mill Bench; south
of Taboose Creek (Figure 24). Google Earth reconnaissance shows areas of similar dark
color to this study, suggesting these flats could be basaltic in composition. Stecker Flat is
approximately 1.75 km2 in area and lies 200 m in elevation above the SNFFZ exposure (Figure
24). Shingle Mill Bench is approximately 1.5 km2 in area and lies 400 m in elevation above the
SNFFZ exposure (Figure 24). A basalt dam/wall was observed up Sawmill Creek while
conducting field work, but was not part of the focus of this study. This interglacial basalt flowed
from an elevation of 2,300 m from a vent on the northern side of Sawmill Canyon through the
steep walled canyon of Sawmill Creek sometime between the Tahoe and Tioga stages of
glaciation (Moore, 1963). Stream erosion of Sawmill Creek cut through and removed a majority
of the basalt that once filled Sawmill Canyon, especially in the lower canyon (Moore, 1963).
Analysis of these areas could provide further insight into understanding this contact and help
solidify the interpretation of the contact being a fault. Understanding and interpreting these areas
could provide further support of a fault interpretation for this study area.
39
Fig
ure
24
. (a
) M
ap
vie
w o
f S
hin
gle
Mil
l B
ench
Fla
t
(so
uth
of
Tab
oose
Cre
ek)
and
Ste
cker
Fla
t (n
ort
h o
f
Tab
oo
se C
reek
) in
rela
tio
n t
o f
ault
s of
the
Sie
rra
Nev
ada
Fro
nta
l F
ault
Zo
ne
(SN
FF
Z)
(blu
e an
d
yel
low
),
Sh
ellh
orn
’s (
20
16
)
stu
dy a
rea
(gre
en),
and
No
rth
of
Saw
mil
l C
reek
3
(NS
C3)
for
this
stu
dy (
wh
ite)
.
Are
as o
f fl
at a
re
hig
hli
gh
ted
by r
ed
circ
les.
(b
)
So
uth
wes
t vie
w o
f
Sh
ingle
Mil
l B
ench
Fla
t an
d S
teck
er
Fla
t d
isp
layin
g
elev
atio
n
dif
fere
nce
s
com
par
ed t
o
Sh
ellh
orn
’s (
20
16
)
stu
dy a
rea
and
NS
C3
fo
r th
is
stu
dy.
Figu
re 2
4.a
Figu
re 2
4.b
40
References
Anderson, E.M., 1951, the dynamics of faulting and dyke formation, with applications to Britain:
Edinburgh, Oliver and Boyd, 191 p.
Argus, D.F., and Gordon, R.G., 1991, Current Sierra Nevada–North America motion
from very long baseline interferometry: Implications for the kinematics of the western
United States: Geology, v. 19, p. 1085–1088, doi:10.1130/0091-
7613(1991)019<1085:CSNNAM>2.3.CO;2.
Beanland, S. and Clark, M. M., 1992, The Owens Valley Fault Zone, Eastern California, and
Surface faulting associated with the 1872 earthquake: U.S. Geological Survey Bulletin.
Bierman, P. R., Clark, D., Gillespie, A., Hanan, B. B., editor; Whipple, K. X.,
1991, Quaternary geomorphology and geochronology of Owens Valley, California;
Geological Society of America field trip. Geological excursions in Southern California
and Mexico, Walawender, Michael J., editor. San Diego, CA: San Diego State Univ., p.
199- 223.
Gadbois, B., 2013, Fault orientation of the Sierra Nevada Frontal Fault Zone in the vicinity of
Lone Pine, California, Undergraduate Thesis, California State University, Fullerton,
Print.
Le, K., Lee, J., Owen, L.A., Finkel, R., 2007, Late Quaternary slip rates along the Sierra Nevada
frontal fault zone, California: Slip partitioning across the western margin of the Eastern
California Shear Zone-Basin and Range Province. Geol. Soc. Am. Bull. 2007, 119 (1/2),
240–256.
Moore, J.G., 1963, Geology of the Pinchot Quadrangle, Southern Sierra Nevada, California,
Geological Survey Bulletin 1130, Washington, U.S. Govt. Print Off,, p. 133-135
Mottle, G., 2014, Evaluation of the Sierra Nevada Frontal Fault System at Bairs Creek in the
vicinity of Manzanar, California, Abstract, California State University, Fullerton, Print.
Phillips, F.M.; Majkowski, L., 2008, The role of low-angle normal faulting in active tectonics of
the northern Owens Valley, California. Lithosphere 2008, 3 (1), 22–36.
Ross, Donald C., 1965, Geology of the Independence Quadrangle, Inyo County,
California, Geological Survey Bulletin 1181-0. U.S. Government Printing Office,
Washington.
Ross, D.C., 1965, Geology of the Independence Quadrangle, Inyo County, California.
Geological Survey Bulletin 1181-0. U.S. Government Printing Office, Washington.
Shagam, G., 2012, Orientation of the Sierra Nevada Frontal Fault Zone near Independence and
Lone Pine, California, Undergraduate Thesis, California State University, Fullerton,
Print.
Shellhorn, A., 2016, Evaluation of the Big Pine Volcanic Field contact relationships along the
Sierra Nevada Frontal Fault Zone north of Goodale Creek in Owens Valley, California,
Undergraduate Thesis, California State University, Fullerton, print.
Slemmons, D.B., Vittori, E., Jayko, A.S., Carver, G.A., Bacon, S.N., 2008, Quaternary fault and
lineament map of Owens Valley, Inyo County, eastern California. Geol. Soc. Am. Map
and Chart 96. p 1-16.
USGS, web, www.usgs.gov, accessed October 2015-September 2016
Varnell, A., 2006, Petrology and Geochemistry of the Big Pine Volcanic Field, Inyo County,
CA, Geological Sciences Department California State Polytechnic University Pomona,
CA, Senior Thesis.
41
Vazquez, J.A., and Woolford, J.M, 2015, Late Pleistocene ages for the most recent volcanism
and glacial-pluvial deposits at Big Pine volcanic field, California, USA from
cosmogenic 36Cl dating, Geochem. Geophys. Geosyst., 16, doi:
10.1002/2015GC005889.
Wakabayashi, J., and Sawyer, T.L., 2001, Stream incision, tectonics, uplift, and the evolution of
topography of the Sierra Nevada, California: Journal of Geology, v. 109, p. 539-562, doi:
10.1086/321962.