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.

1

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

2

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

3

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).

4

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.

5

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

6

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).

7

Figu

re 4

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re 4

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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

9

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

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ithin

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rea

(only

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arked

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ound a

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).

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

13

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.

14

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

15

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

19

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.

21

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

24

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

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