An Undergraduate Thesis Presented to The Faculty of California State University, Fullerton Department of Geological Sciences

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1 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

2 DETERMING THE NATURE OF THE CONTACT BETWEEN THE EASTERN NEVADA MOUNTAIN FRONT AND THE BIG PINE VOLCANIC FIELD SOUTH OF GOODALE CREEK IN OWENS VALLEY, CALIFORNIA SIERRA An Undergraduate Thesis Presented to The Faculty of California State University, Fullerton Department of Geological Sciences DETERMINING THE NATURE OF In Partial Fulfillment THE CONTACT BETWEEN THE of the Requirements for the Degree Bachelor of Science EASTERN SIERRA NEVADA in Geology MOUNTAIN FRONT AND THE BIG PINE VOLCANIC FIELD SOUTH OF GOODALE CREEK IN By Jazmine Titular September 2016 OWENS VALLEY, CALIFORNIA Jazmine Titular Bachelors of Science in Geology California State University, Fullerton Undergraduate Thesis, September 2016 Advisor: Dr. Phil Armstrong Dr. Phil Armstrong, Faculty Advisor

3 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 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 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.

4 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 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 1

5 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 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 Philips and Majkowski (2011) measured multiple fault planes to the north in the Bishop area which resulted in dips ranging from (Figure 2). Previous thesis students analyzed fault outcrop patterns to the south in areas stretching from Independence to Lone Pine and measured 2

6 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). 3

7 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 To the south, stretching from Independence to Lone Pine, previous thesis students analyzed fault locations and calculated dips ranging from (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.

8 dips ranging from (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 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 m, while the western edge of the White and Inyo Mountains rise more gently and only reach heights ranging from m. However, in the northernmost areas of the White Mountains, relief reaches up 2700 m (Phillips 5

9 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).

10 Figure 4.b Figure 4. (a) Westward view of study area from Highway 395. Basalts of the Big Pine Volcanic Field (BPVF) can be observed in direct contact with the granite along the mountain front. Creek locations identified for comparison to aerial view. Road and wooden posts in foreground for scale. (b) Aerial view of study area for a better understanding of the contact relationships between the granite and basalt. Creek locations identified for spatial context and reference. Figure 4.a 7

11 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) 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 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 8

12 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 ka in areas west of Aberdeen (Vazquez and Woolford, 2015) 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 9

13 (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 km 2 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 km, which could be the result of the kinematics that 10

14 11 Figure 5. General geologic map adapted from Vazquez and Woolford (2015). Red box highlights area of Big Pine Volcanic Field (BPVF) located within study area (only the northern 2/3 of study area within this map). Volcanic vents are marked by asterisks and found along the mountain front in a similar orientation as the Sierra Nevada Frontal Fault Zone (SNFFZ).

15 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 ~ 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 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 12

16 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. 13

17 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 14

18 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. 15

19 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. 16

20 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. 17

21 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 (R 2 =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 18

22 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. 19

23 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. 20

24 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 21

25 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. 22

26 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 23

27 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. 24

28 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. 25

29 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. 26

30 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 R 2 value of 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 27

31 Vents 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. 28

32 Contact between BPVF and mountain front Contact between BPVF and mountain front 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. 29

33 dip observed in the field. The strike appears to match up almost perfectly with the contact measured, but results in a lowest R 2 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 R 2 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 30

34 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). 31

35 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. 32

36 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. 33

37 of the contact orientation (N30W, 27 E), which is consistent with measurements from SSC and NSC 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 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 34

38 Distance (m) Figure 22. Comparison of average Sierra Nevada Mountain front slope angle and average contact dip from Shellhorn (2016). Analysis includes multiple elevation profiles along the mountain front. The average slope is 22 E and the average dip of the contact is 33 E farther north (Shellhorn, 2016). 35

39 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 E. Just south of Bishop in Aberdeen between Taboose and Goodale Creek, Shellhorn (2016) calculated dips ranging from E. This study calculated dips in an area directly south of Shellhorn between Goodale and Sawmill Creek, resulting in a range from E. South of this area near Independence at Shepard and Independence Creek, Shagam (2012) calculated dips ranging from E. To the south in the vicinity of Manzanar near Bair Creek, Mottle (2014) calculated dips ranging from 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. 36

40 37 Figure 23. Locations of all studies conducted along the SNFFZ. To the north in Bishop, Phillips and Majkowski (20011) calculated dips ranging from North of this study area, Shellhorn (2016) calculated dips of This study area has calculated dips from To the south, stretching from Independence to Lone Pine, previous thesis students analyzed fault scarps and calculated dips ranging from (Shagam, 2012; Gadbois, 2013; Mottle, 2014).

41 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 km 2 in area and lies 200 m in elevation above the SNFFZ exposure (Figure 24). Shingle Mill Bench is approximately 1.5 km 2 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. 38

42 Figure 24.a Figure 24.b Figure 24. (a) Map view of Shingle Mill Bench Flat (south of Taboose Creek) and Stecker Flat (north of Taboose Creek) in relation to faults of the Sierra Nevada Frontal Fault Zone (SNFFZ) (blue and yellow), Shellhorn s (2016) study area (green), and North of Sawmill Creek 3 (NSC3) for this study (white). Areas of flat are highlighted by red circles. (b) Southwest view of Shingle Mill Bench Flat and Stecker Flat displaying elevation differences compared to Shellhorn s (2016) study area and NSC3 for this study. 39

43 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 , doi: / (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 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), Moore, J.G., 1963, Geology of the Pinchot Quadrangle, Southern Sierra Nevada, California, Geological Survey Bulletin 1130, Washington, U.S. Govt. Print Off,, p 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), Ross, Donald C., 1965, Geology of the Independence Quadrangle, Inyo County, California, Geological Survey Bulletin U.S. Government Printing Office, Washington. Ross, D.C., 1965, Geology of the Independence Quadrangle, Inyo County, California. Geological Survey Bulletin 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 USGS, web, 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. 40

44 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: /2015GC 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 , doi: /