QUATERNARY FAULTING OF DESCHUTES COUNTY, OREGON
HUMBOLDT STATE UNIVERSITY
By
John M. Wellik
A Thesis
Presented to
The Faculty of Humboldt State University
In Partial Fulfillment
Of the Requirements for the Degree
Master of Science
Environmental Systems: Geology
May, 2008
QUATERNARY FAULTING OF DESCHUTES COUNTY, OREGON
HUMBOLDT STATE UNIVERSITY
By
John M. Wellik
Approved by the Master's Thesis Committee:
______Mark A. Hemphill-Haley, Geology Professor Date
______Raymond M. Burke, Committee Member Date
______John D. Longshore, Committee Member Date
______Sharon L. Brown, Graduate Coordinator Date
______Chris A. Hopper, Interim Dean Date Research, Graduate Studies & International Programs
ABSTRACT
QUATERNARY FAULTING OF DESCHUTES COUNTY, OREGON
John M. Wellik
Sixty-one normal faults were identified in a 53-kilometer long by 21-kilometer wide northwest-trending zone in central and northern Deschutes County, Oregon. The faults are within the Tumalo and Sisters fault zones and the Northwest Rift Zone, and extend from Newberry Volcano to Black Butte. Faults are identified in and near the population centers of Bend, Redmond, Sisters, and Tumalo. The investigation identified displacement of volcanic flows dated at 24 ± 14 ka using K/Ar and 39 ± 6 ka using 40Ar/
39Ar, displacement of several prominent pyroclastic deposits, displacement of multiple undated volcanic flows, and displacement of undated sedimentary deposits; 7,000-year- old Mazama ash is unfaulted. Displacement of deposits in the southern portion of the study area relative to displacement in the northern portion is interpreted having occurred more recently and is generally of greater magnitude. Evidence of fault reactivation over time was found, as older rock units are displaced more than younger ones along the same segment of a fault.
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ACKNOWLEDGEMENTS
Many thanks and eternal indebtedness to the following: Deschutes County personnel and residents, Deschutes County Commissioners office, Deschutes County
Commissioner Dennis Luke for establishing project financing, Deschutes County
Geographical Information Systems Department, Deschutes National Forest employees
Larry Chitwood and Bob Jensen, Humboldt State University Geology Department professors and staff, Bud Burke, Mark Hemphill-Haley, John Longshore, Susan
Cashman, Harvey Kelsey, Humboldt State University fall 2002 Quaternary Field studies class (Geo 554), Ian and Bonnie (Mrs.) Pryor, Diane Sutherland, Michelle Roberts,
Ronna Bowers, Jay Stallman, Todd Williams, Jay Patton, Rick Murphy, LACO
Associates, my dad and sisters, especially Beth for hiking with me, and Barb and Jim
Wenzinger. Thebe was a great field companion. Thanks to Cynthia Werner and Sharon
Brown for guiding me through paper formatting and with editing help.
A special note of thanks to my lovely wife Anne for her seemingly limitless patience, love, support, care, inspiration and constant encouragement; I would not be writing this section without her. I love you Anne. Dean, you mean the world to me; I hope this provides a good example. Here it is mom.
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TABLE OF CONTENTS
ABSTRACT...... iii
ACKNOWLEDGEMENTS...... iv
TABLE OF CONTENTS...... v
LIST OF TABLES...... vii
LIST OF FIGURES ...... viii
LIST OF APPENDICES...... x
INTRODUCTION ...... 1
Geologic Setting...... 2
Previous Work ...... 4
METHODS ...... 6
DEPOSITS...... 8
Quaternary Deposits...... 10
Tertiary Deposits...... 14
TUMALO AND SISTERS FAULT ZONES AND THE NORTHWEST RIFT ZONE ...... 15
Tumalo Fault Zone...... 15
Sisters Fault Zone ...... 16
Bend Area Faults...... 17
Northwest Rift Zone ...... 17
Map Scale Fault Descriptions ...... 18
Outcrop Scale Fault Description...... 19
v
Relation of Faults and Volcanic Edifices...... 20
Evidence of Fault Timing ...... 22
Evidence of Fault Reactivation...... 25
DISCUSSION...... 27
SUMMARY AND CONCLUSIONS ...... 30
ADDITIONAL GEOLOGIC QUESTIONS AND STUDY OPPORTUNITIES ...... 31
TABLES ...... 32
FIGURES...... 36
PHOTOGRAPHS ...... 48
REFERENCES ...... 58
vi
LIST OF TABLES
Table Page
1. Fault Data…………………………………………………………….………….. 33
2. Fault and Stratigraphy Matrix…………………………………………………… 34
vii
LIST OF FIGURES
Figure Page
1. Study Area Map…………………………………………………………………... 37
2. Regional Geologic Structures Relative to the Study Area………………………... 38
3. Correlation of Rock Units………………………………………………………… 39
4. Tumalo Fault Zone………………………………………………………………... 40
5. Sisters Fault Zone………………………………………………………………….41
6. Bend Area Faults…………………………………………………………………..42
7. Northwest Rift Zone…………………………………………………………….....43
8. Photograph Legend………………………………………………………………...44
9. Volcanic Structures Relative to Study Area Faults……………………………….. 45
10. Potential Tertiary Cinder Cones and Flow Lobes near Tumalo Reservoir…….. ..46
11. Log of a portion of the south wall of the Tumalo fault exploratory trench (TT1). 47
Photograph Page
1. Fault T7 in Quaternary sand at southeastern corner of the intersection of Highway 126 and Cloverdale Road………..…………………………………………………... 49
2. Fault T19 in Quaternary basalt flows of Newberry Volcano in southern Bend; three- story house built on up-thrown side for scale………………………………………...49
3. Fault S6 in Tertiary Deschutes formation lava flows parallel to Barr Road, north of Tumalo……………………………………...……………………….………………. 50
4. Fault B2 in Quaternary basalt of Newberry Volcano, south of Bend near Horse Butte……………………………………...……………………………………….…. 50
viii
5. Fracture in Quaternary Tumalo Tuff with fracture fill from the overlying gravel deposit along the Tumalo Fault (T1)….……………….……………………………. 51
6. Silica-lined fracture in up-thrown (western) side of fault T7 at Cloverdale and Highway 126………………………………………………………...…………...... 52
7. Vertical fractures in Quaternary Shevlin Park Tuff (Qsp) in Anderson pit in Bend. ………………………………………………………………………………..………53
8. Fault S10 in Quaternary Tumalo Tuff exposed in a borrow pit parallel to Tumalo Market Road……………...………………………………………………….……….54
9. Fault T19 in Quaternary Tumalo Tuff at Anderson Pit in Bend...………………. 55
10. Fault B4 in Quaternary basalt of Newberry Volcano south of Knott Landfill in southern Bend...……………………….………………………………….…………..55
11. Fault B4 transects Highway 20 in central Bend, with cars for scale. White car is on the up-thrown (western) side of the fault…………………………………………... 56
12. Fault T1, the Tumalo Fault, in Quaternary sand and Tertiary Deschutes formation lava flows at Bull Flat……………………………………………………………….. 56
13. Fault B3 in Quaternary andesitic basalt of Pilot Butte, northeast of Pilot Butte in Bend………………………………………………………………………..………... 57
14. Fault S16 in Tertiary Deschutes formation pyroclastic flow deposits and lava flows. ………………………………………………………………………………………..57
Map
Plates 1 and 2. Tumalo and Sisters Fault Zones Map and cross-sections.....Back Sleeve
ix
LIST OF APPENDICES
Appendix Page
A. Map Reference……………………………………………………………...... 62
B. Fault Zone Description………………………………………………………… .63
x
INTRODUCTION
A portion of Deschutes County, Oregon is traversed by a 53-kilometer long and
21-kilometer wide northwest-trending zone of faulting (Plate 1). The Tumalo and Sisters
Fault Zones and the Northwest Rift Zone extend from Newberry Volcano to Black Butte.
The cities of Bend and Redmond and the ranching communities Sisters and Tumalo lie within or border the study area (Figure 1). Previous investigations recognized
Pleistocene fault activity within the study zone (Pezzopane, 1993; Pezzopane and
Weldon, 1993; Geomatrix Consultants, 1995; Hemphill-Haley, project proposal, 1994) and describe structural control of magma emplacement at Newberry Volcano, generally in the form of cinder cone distribution (Taylor et al., 2005). Late Quaternary timing, style, and distribution of faulting and earthquakes within the Tumalo and Sisters fault zones and Northwest Rift Zone was previously unknown.
I conducted detailed field investigations, including fault and surface deposit mapping, along lineaments displacing deposits of different origins and ages, and within areas of likely Holocene and Pleistocene deposits, such as active and inactive stream valleys and alluvial fans. These features were recognized during aerial photo and topographic map interpretation, analysis of Geographic Information System (GIS) data, and during the course of fieldwork. I focused field investigations on faulting of
Quaternary surface deposits in an effort to characterize the distribution of surface rupture events within the field area.
1 2 The study area is in the central and northern portions of Deschutes County in central Oregon, east of the Cascade volcanic arc (Figure 2). Urbanization across the fault zones has increased dramatically during the last decade, due in part to rapid population growth in the Bend area. Area development has resulted in removal and burial of faulting evidence contained within the top several to tens of meters of the stratigraphic column.
Logging in the Deschutes National Forest on the Cascades eastern slope has occurred for more than 60 years, which, while providing excellent access via logging roads to the study area’s western portion, has also led to destruction of several potentially illuminating fault exposures. Active and historic rock mining has often targeted exposures along fault traces.
Geologic Setting
The study area is located in the Cascade Range back arc portion of the Cascadia
Subduction Zone trench – arc – back arc system (Figure 2). According to Uyeda and
Kanamori (1979) geologic features that may be found in each portion of a trench – arc – back arc setting include thrust faulting and compression related features in the trench portion, arc volcanism, and back arc extension. Geologic features in the study area include extensional tectonic surface features such as normal faults, horsts and grabens, volcanic flows resulting from eruptions from cinder cones on the eastern flank of the
Cascade Range, and multiple cinder cones aligned along faults (Plate 1). Cole et al.
(1995) stated that these types of geologic features are common to back arc settings. A volume of articles describing back arc tectonic features related to volcanic arcs around
3 the Pacific Rim was compiled by Taylor (1995) and includes descriptions of fault surface rupture features in the Taupo Volcanic Zone back arc in New Zealand.
The study area is situated between several geologic features of prominence, including the northern margin of the Basin and Range Province, the Brothers Fault Zone,
Newberry Volcano, the Cascade Arc and Green Ridge (Figure 2).
According to Donath (1962) one of the classic structural features of the central
Oregon Basin and Range Province is orthorhombic, normal fault-bounded extensional structures as long (100 km) and wide (20 to 40 km) basins enclosed by ranges typically exhibiting several hundred meters of vertical relief. Examples of these types of structures include the Summer Lake basin, Slide Mountain and Abert Rim southeast of the study area (Figure 2). A geologic overview of the Basin and Range Province, including discussions of topography and structural history of the different regions is provided by
Hunt (1979). Eaton (1979) provides a discussion of the geophysics, tectonics and resources of the various Basin and Range Province regions.
The Brothers Fault Zone, a Miocene, west-northwest trending 300 km long zone of normal faults (Lawrence, 1976) terminates southeast of the study area, near the northeast flank of Newberry Volcano. The Brothers Fault Zone is considered inactive by various authors (Pezzopane, 1993; Pezzopane and Weldon, 1993; Geomatrix Consultants,
1995).
Newberry Volcano, south of the study area, is an off-axis Cascade Arc volcano
(Jensen and Chitwood, 2000; Jensen, 2000) that has experienced multiple late Quaternary eruptions (Jensen and Chitwood, 2000; Jensen, 2000; Donnelly-Nolan et al., 2000;
4 Donnelly-Nolan, 2003). Volcanic flows from Newberry Volcano cover much of the
Bend area east of the Deschutes River (Plate 1) and are discussed in further detail in the discussion on deposits within the field area. The La Pine graben is situated west of
Newberry Volcano, and the Walker Rim Fault Zone and Chemult graben are southwest of
Newberry Volcano (Figure 2).
Conrey (1985) recognized Green Ridge, at the northwest end of the study area
(Figure 2), as a result of a now inactive west-dipping normal fault, and has proposed that the Green Ridge fault may be the eastern margin of the Cascade graben.
Previous Work
Previous geologic investigations recognized faulting in the study area; however, much of the work performed to date focused primarily on glacial and volcanic stratigraphy and petrology of volcanic flows. Published and unpublished investigations by Peterson et al. (1976), McDannel (1989), Conrey (1985), Priest (1990), Taylor (1990),
Taylor and Ferns (1994), MacLeod et al. (1995), Jensen (2000), Jensen and Chitwood
(2000), Mimura (1992), Champion et al. (2002), Donnelly-Nolan et al. (2000), and
Sherrod et al. (2004), among others, have begun to establish a more thorough understanding of sources and ages of deposits in the area, and evolution of the Cascade volcanic arc. Several of these studies describe portions of study area fault zones.
Previous fault investigations summarize regional tectonic history and provide fault characteristic information, including estimates of activity and potential earthquake magnitude (Geomatrix Consultants, 1995), contained brief descriptions and
5 interpretations of tectonic activity and central Oregon tectonic development (Pezzopane,
1993; Pezzopane and Weldon, 1993), and discussions on regional tectonic development
(Lawrence, 1976; Donath, 1962). The origin and role of the study area faults is unclear.
It has been suggested that study area faults form the eastern margin of the Cascade
Graben (Taylor, 1981) or function as part of the Basin and Range province northern termination (Lawrence, 1976). In addition to published studies, area faults have been investigated during the course of geologic consulting for home, business and infrastructure construction, and during informal investigations.
METHODS
Stereographic aerial photographs, spanning nearly 60 years in time and varying in scale from 1:25,000 to 1:40,000, were utilized for identification and interpretation of topographic features; these photographic sets comprise black and white, false color, and real color images. I used stereo photograph pairs to identify fault traces, fault-related geomorphic features, volcanic flows and cinder cones, sedimentary deposits, stream
courses, and water bodies, and I marked them on Mylar overlays. I transferred this
information to USGS 1:24,000 7.5-minute topographic base maps for use in the field and
to compile Plate 1. In addition to creating hard copies, I entered stratigraphic data and
fault data into a GIS database using ArcView 3.2 for creation of figures for the project.
A reference list of map, digital raster graphic, digital elevation model data used in this
study is provided in Appendix A.
I performed field work, consisting of “ground truthing” faults and other features
mapped from aerial photographs and topographic maps, and describing deposits during
the summers of 2001 and 2002.
I inspected 35 faults in a study area of approximately 920 square km. I prioritized
lineaments for field inspection and further study based on displacement of Quaternary
alluvial deposits, location near densely populated areas, and the likelihood of recent fault
activity.
Several road cuts and pre-existing excavations are ideally located for inspection
of fault and stratigraphic features, such as fracturing and displaced deposit
6 7 characterization. I did not find any samples suitable for 14C age dating in road cuts and excavations that I encountered.
DEPOSITS
Eastern Cascade volcanic and glacial deposits comprise the primary surface deposits in the study area (Plate 1). Sherrod et al. (2004) compiled an extensive description of surface deposits of the Bend 30- by 60-minute quadrangle map that serves as the basis for unit descriptions in this study. Lithologic descriptions are summarized from Sherrod et al. (2004) unless otherwise noted (Figure 3).
Several methods for dating deposits are utilized by the various authors cited in the
Sherrod et al. (2004) compilation; included among these are use of oxygen isotope stages, magnetic polarity, and atomic isotopes. Brief descriptions of these dating methods follow.
Glacial deposit ages are discussed in this study in the framework of oxygen isotope stages. Oxygen isotope stages describe periods of glacial ice advances and retreat.
Due to changes in ice volume, sea level fluctuates during the course of glacial advance and retreat, with lower sea levels occurring during periods of ice accumulation (i.e. glacial periods) and higher sea levels occurring during periods of ice melting (i.e. interglacial periods). As oxygen 16 (16O) has a smaller mass than oxygen 18 (18O), water comprised of 16O molecules evaporates preferentially to water comprised of 18O molecules, resulting in water with a higher ratio of 18O to 16O. This ratio fluctuation is recorded in carbonate shells of foraminifera contained in marine sediments and has been calibrated to glacial and interglacial events, providing timing of ice advance and retreat
(Williams et al., 1988; Mix, 1992; Poag et al., 1983; Prothero, 1994). Mix (1992)
8 9 provides a discussion of the oxygen isotope stage system of glacial/interglacial numerical classification. In brief, even numbered oxygen isotope stages correlate to glacial events, while odd numbered stages correlate to interglacial events, with the most recent glacial event labeled as oxygen isotope stage 2. Blackwelder (1948) provides a discussion of glacial and postglacial periods and features of the different regions of the Great Basin.
Sherrod et al. (2004) note the magnetic polarization of several volcanic deposits.
Magnetic polarization, especially of iron-rich rocks such as basalt, is used as a means of providing timing of cooling of volcanic flow and hot pyroclastic deposits. As recorded in the rock record (Stacey and Banerjee, 1974; Tarling, 1983; Irving, 1964), the earth’s magnetic field has varied in pole location, intensity, and polarization over time (Cox et al., 1965). Sherrod et al. (2004) reference normal and reverse magnetic polarization as a means of refining the relative age of a deposit based on stratigraphic position, where atomic isotope ratio data are not available. The Brunhes-Matayama magnetic reversal dated at approximately 760,000 years before present (Cox et al., 1965) is the primary magnetic reversal event discussed by Sherrod et al. (2004).
Several deposits reported in Sherrod et al. (2004) were dated using isotopic dating techniques. Isotopic dating uses predictable decay rates of various isotopes contained within minerals to provide an age (Dicken, 1995; Hoefs, 1980; Faure, 1986; Dalrymple and Lanphere, 1969). This age is often assumed as the age of the rock deposit.
10 Quaternary Deposits
Quaternary deposits in the study area consist of volcanic flows, pyroclastic flows, alluvium, and glacial outwash deposits of oxygen isotope stage 2 through oxygen isotope stage 6. I described the deposits in the field and identified them based on criteria of
Sherrod et al. (2004). An important deposit in the study area is a yellowish sandy ash, identified as Mazama ash, mixed with other various fine- and coarse-grained sediments
(Chitwood, 2002); this deposit overlies outcrops of older rocks in much of the study area, but due to the extensive nature of the deposit, I have not included it on Plate 1. The
Mazama ash mix deposit is up to 1 meter thick at several locations (i.e. Anderson Pit in
Bend).
Three Quaternary pyroclastic ash flow deposits provide stratigraphic markers that can be used to estimate timing of surface rupture events of Tumalo Fault Zone and Sisters
Fault Zone faults. No precise sources of the pyroclastic flows have been suggested by previous authors; however, Sherrod et al. (2004), and McDannel (1989) placed the sources for all three pyroclastic flows west and southwest of the study area, as indicated by imbrication of pumice within the deposits.
The youngest of the three pyroclastic flows, Shevlin Park Tuff (Qsp), is a dark gray to black pyroclastic flow (Sherrod et al., 2004). Located primarily in the study area’s southwestern part, west and northwest of the city of Bend (Plate 1), Qsp deposits range from 45 m to less than 1 m thick (Sherrod et al., 2004). Qsp is dated at 170 to 270 ka, based on stratigraphic position of distal fallout tephra in lakebeds of the northern
11 Great Basin (Sherrod et al., 2004). An 40Ar/ 39Ar age of 260 ± 15 ka was reported for this deposit (Sherrod et al., 2004).
The intermediate punk pyroclastic flow, the Tumalo Tuff (Qtt), is associated locally with the underlying pumiceous Bend Pumice fallout deposit; both units are thought to have been generated by the same volcanic event (Sherrod et al., 2004), and, as such, both units are identified as Qtt on the map (Plate 1). Qtt is broadly distributed from north of Shevlin Park to a broad drainage north of Bull Flat, referred to informally as
Less Flat in this study (Plate 1), and is exposed at the surface in Bull Flat and in the banks of the Deschutes River near Tumalo (Plate 1). Combined, the two deposits are approximately 24 m thick, with Bend Pumice accounting for approximately 11 m of the total thickness (Sherrod et al., 2004). The ashflow tuff ranges in age between 300 and
400 ka, based on several K/Ar ages (Sherrod et al., 2004).
The oldest study area pyroclastic flow, the Desert Springs Tuff (Qds), is a 5 to 11 m thick rhyodacitic ashflow tuff estimated at approximately 600 ka, based on correlation of distal tephra and normal polarization (Sherrod et al., 2004). Qds is primarily located along Highway 20 in the central portion of the field area, and the type locality is at Desert
Spring, south of Fryrear Butte (Sherrod et al., 2004) (Plate 1).
There are six Newberry Volcano and eastern Cascade basalt, balsaltic andesite, and andesite deposits in the study area (Plate 1). Quaternary basalt of Newberry Volcano
(Qbn) consists of multiple Pleistocene vesicular basalt flows from Newberry Volcano northern flank vents, south of Bend (Sherrod et al., 2004). Qbn extends across much of the southeastern study area, east of the Deschutes River, and underlies most of Bend
12 (Plate 1). Qbn comprises the majority of the eastern bank of the Deschutes River in the
study area. Ages of Qbn range from approximately 80 to 200 ka, based on an 40Ar/ 39Ar age of 78 ± 9 ka (Champion et al., 2002) and an estimated age for Stevens Cave basalt between 100 and 200 ka (Champion et al., 2002). Qbn flows typically range in thickness from between 5 and 7 m (Sherrod et al., 2004).
Quaternary andesite (Qa) is mapped as undifferentiated porphyritic lava flows from the High Cascades (Plate 1) with normally polarized magnetization (Sherrod et al.,
2004). Based on mapped deposits illustrated on the Sherrod et al. (2004) base map, Qa is chiefly confined to the southwestern portion of the study area.
Quaternary basalt (Qb) consists of undifferentiated and undated eastern Cascades
Pleistocene and Holocene lava flows (Plate 1) (Sherrod et al., 2004). Several Qb flow lobes extend from the eastern Cascade slope toward the western portion of the field area
(Sherrod et al., 2004).
Quaternary basaltic andesite (Qba) primarily consists of undifferentiated and undated lava flows from the High Cascades (Plate 1) (Sherrod et al., 2004). A Qba flow originating from Klawhop Butte is dated at 24 ± 14 ka using K/Ar and 39 ± 6 ka using
40Ar/ 39Ar (Donnelly-Nolan et al., 2000), and extends from Klawhop Butte to southern
Bend (Sherrod et al., 2004) (Plate 1).
Quaternary basaltic andesite of Pilot Butte (Qbapb) predates and locally underlies
Qbn flows in Bend (Sherrod et al., 2004) (Plate 1). Age of the cone and flows is 188 ka ±
42 ka, based on 40Ar/39Ar and K/Ar ages (Donnelly-Nolan et al., 2000).
13 Quaternary basalts of Plainview (Qbpp) are widespread lava flows exposed in
Deep Canyon and south-southeast of Sisters (Sherrod et al., 2004) (Plate 1). The normally polarized flows overlie Qds and therefore are younger than 600 ka (Sherrod et al., 2004).
Various named and unnamed cinder cones occupy the Cascade Range eastern slope, on the western margin of the study area (Plate 1), and occur along or between study area faults.
Glacial and fluvial deposits include Quaternary alluvium (Qal) of modern stream and river courses, and reworked glacial outwash and flood deposits of oxygen isotope stage 2 to oxygen isotope stage 6 ages. Qal consists of unconsolidated sands and gravels located primarily in active and ephemeral streambeds and valley floors (Plate 1) (Sherrod et al., 2004).
Quaternary outwash and till of the Suttle Lake advance (Qos/Qgs, respectively) are late Pleistocene deposits (oxygen isotope stage 2, between 11 – 20 ka (Sherrod et al.,
2004)) and are found within the study area immediately around and northwest of Sisters
(Plate 1).
Quaternary Sands (Qs) consists of undifferentiated sands and gravels, middle to late Pleistocene (oxygen isotope stage 6 and younger) outwash and flood deposits
(Sherrod et al., 2004). Qs deposits cover much of the central study area (Plate 1).
14 Tertiary Deposits
The Deschutes Formation (Td) is the primary study area Tertiary deposit (Plate
1). Td comprises multiple pyroclastic deposits and is capped by vesicular basalt flows inferred to have erupted from various small named and unnamed, fault-marginal cinder cones (McDannel, 1989). K/Ar ages greater than 3.7 Ma were obtained for capping basalt in the north central portion of the study area (McDannel, 1989).
TUMALO AND SISTERS FAULT ZONES AND THE NORTHWEST RIFT ZONE
The Tumalo and Sisters Fault Zones and the Northwest Rift Zone are comprised of 61 faults ranging in length from less than one kilometer to approximately 36 kilometers (Table 1). Individual faults are segregated into each of the fault zones that have been adapted from previous work (Geomatrix Consultants, 1995; Jensen and
Chitwood, 2000), and faults are labeled in the order identified during aerial photograph interpretation and during the course of fieldwork (Table 1). Written descriptions of individual faults are included in Appendix B.
General descriptions of the Tumalo and Sisters Fault Zones and the Northwest
Rift Zone, map and outcrop scale fault descriptions, the relation of faults to Quaternary and Tertiary volcanic edifices, evidence of timing of fault surface ruptures, and indications of fault reactivation over time follow.
Tumalo Fault Zone
The Tumalo Fault Zone is comprised of 21 faults ranging in length from less than
1 km to more than 36 km (Table 1). The Tumalo fault zone stretches from Newberry
Volcano’s northern flanks to north of the town of Sisters, projecting toward Black Butte and the Green Ridge fault zone (Plate 1, Figure 4). The eastern Tumalo fault zone borders the western Sisters fault zone in the north, Bend area faults in the southeast, and the Northwest Rift Zone in the south. The western boundary of the Tumalo Fault Zone
15 16 has not been fully established in the relatively young surface of the eastern Cascade slope.
Tumalo Fault Zone faults are parallel to sub-parallel in plan view (Plate 1, Figure
4) and fault strikes vary between N36°W and N10°W, with an average strike of N23°W.
Observed vertical surface separations along Tumalo Fault Zone faults tend to vary on the order of several meters to tens of meters along strike. For instance, fault T19
(Table 2, and Appendix B) maximum vertical surface separation nears 15 m in mid-
Pleistocene Qbn (78ka) lava flows south of Bend, whereas Qtt (400ka) vertical surface separation is approximately 7 m west of Bend.
Sisters Fault Zone
The Sisters Fault Zone is comprised of 28 faults, splays and lineaments ranging in length from 25 km to less than 1 km (Figure 5, Table 1). The Sisters Fault Zone stretches from the northern margin of Qbn deposits southeast of Tumalo to approximately 14 km north of Highway 126, projecting toward Tertiary shield cones Little Squaw Back and
Squaw Back Ridge (Plate 1). The Sisters Fault Zone is bounded on the west by the
Tumalo Fault Zone, while Long Butte and Cline Buttes bound the eastern margin.
The overall fault trend of Sisters Fault Zone faults tends to be broadly concave to the southwest, and faults are parallel to sub-parallel in plan view. Fault strikes vary between
N44°W and north-south, with an average of N25° W.
Vertical surface separations vary along trend, with greater surface separation typically occurring in older Td deposits than in Qs. Deschutes River Qal in the vicinity
17 of Tumalo is unfaulted. Along strike of fault S3 surface displacement of Qs is approximately 2 m and Td is displaced approximately 5 m (Table 2); along strike of fault
S9 Qs is displaced less than 1 m and Td is displaced approximately 5 m.
Bend Area Faults
Bend area faults consists of four faults with splays and antithetic faults, ranging in length from more than 20 km to less than 1 km (Figure 6). Bend area faults extend from
Newberry Volcano’s northern flanks near Coyote Butte to approximately 2 km north of the junction of Highways 20 and 97 (Plate 1, Figure 6). Fault T19 provides the western boundary to Bend area faults, and surface deformation of Newberry volcanic flows is not apparent east of Fault B2.
Vertical surface separation varies along trend, with greater separation occurring on Bend’s southern margin, and in older Pilot Butte flows. Northern portions of faults
B1, B2 and B4 displace Qbn by up to 2m, with displacement diminishing to zero at the northernmost parts of the faults, while the southern sections of these faults displace Qbn by an estimated 12 m to 20 m. Fault B3 displaces Qbn approximately 2 m and Qbapb by approximately 10 m immediately northeast of Pilot Butte. Bend area fault strikes vary in orientation between N45°W and N13°W, and the zone has an average trend of N26°W.
Northwest Rift Zone
The Northwest Rift Zone is comprised of eight normal faults, splays and lineaments ranging in length from 4.7 km to less than 1 km (Figure 7). The Northwest
18 Rift Zone stretches from approximately 2 km west of Klawhop Butte to Tumalo Creek west of Bend, and is bordered by Tumalo Fault Zone and Bend area faults in the north and east, respectively. The Northwest Rift Zone western extent lies approximately 3 km west of Green Mountain, and a northwest trending chain of cinder cones aligned along
Newberry Volcano’s northwestern slope defines the southern Northwest Rift Zone extent
(Plate 1, Figure 7).
Fault trends vary between N37ºW and N12ºW, with an average trend of N25°W.
Vertical surface separations vary along trend. Based on topographic map
evidence, the greatest vertical surface separation occurs in older Green Mountain deposits
and in volcanic flows located west of the Deschutes River that emanate from the Cascade
Arc (Plate 1).
Map Scale Fault Descriptions
Study area faults are typically expressed at the surface as linear to curvilinear
normal faults with minor deflections and occasional steps in strike at the map scale (Plate
1). Map scale structural features such as horsetail splays and narrow horst and graben
features were recognized on multiple faults during the course of the study (Plate 1).
A prominent map scale feature is a horsetail-type splay that occurs along the Bull Flat
section of the Tumalo Fault, where faults T7, T8, and T9 deflect off the strike of the main
Tumalo Fault to more northerly strikes (Plate 1, and Figure 4).
19 Steps in strike occur on the Tumalo Fault at Less Flat (Plate 1, Figure 4), also along a portion of fault T5 on the west side of Less Flat (Plate 1, Figure 4), as well as on multiple Sisters Fault Zone faults (Plate 1, Figure 5).
Several Sisters Fault Zone faults form alternating horst and graben sequences when viewed at the map scale (Plate 1, Figure 5). Faults S1 and S2 combine to form a horst structure at Smokey Butte, a volcanic center of Tertiary age (McDannel, 1989).
Faults S3 through S6 combine to form a graben (S3 and S4)- horst (S4 and S5)- graben
(S5 and S6) sequence east of Smokey Butte (Plate 1, Figure 5). Jensen and Chitwood
(2000) interpreted a graben between faults B1 and B4 in the area of Knott Landfill.
Lateral separation may be present on study area faults; however evidence of lateral separation in the form of laterally displaced deposits or stream courses was not observed.
Outcrop Scale Fault Description
Study area faults are typically identified as gentle breaks in slope when observed in glacial-fluvial sediments at outcrop scale (Photograph 1), while faults found in volcanic lava flow deposits commonly maintain vertical to nearly vertical scarps
(Photograph 2). Blocky colluvial wedges commonly obscure multiple fault scarps in volcanic flow deposits (Photographs 2, 3 and 4). A legend of photograph locations is included as Figure 8.
I observed vertical fractures, typically lined with silica precipitant and occasionally gravel-filled, on several faults in glacial-fluvial sediments exposed in
20 borrow pits excavated into the up-thrown side of faults. A borrow pit exposure in Qs and
Qtt deposits near Tumalo Reservoir contains vertical fractures with fracture fill from overlying glacial deposits and some silica cementation (Photograph 5), and a borrow pit excavated into Qs deposits on the up-thrown side of fault T7 in Cloverdale contains silica-lined vertical fractures (Photograph 6). Vertical fractures also occur in several pyroclastic deposits, including densely welded Qsp at Anderson Pit, where vertical fractures up to 60 cm wide extend for more than 50 m from the base of the exposure
(Photograph 7), and in borrow pit excavations in Qtt deposits at Tumalo Reservoir
(Photograph 4) and along Tumalo Market Road (Photograph 8).
Relation of Faults and Volcanic Edifices
Structural control of magma emplacement around Newberry Volcano, generally in the form of cinder cone distribution, was explored by Taylor et al., (2005), using several statistical analyses of cinder cone distribution on the north and south sides of the volcano. The analyses reveal that cinder cone alignment is not random and that alignment of cones correlates strongly with the orientation of fault segments of the
Brothers Fault Zone, the Tumalo Fault Zone, and the Northwest Rift Zone (Taylor et al.,
2005).
In another paper Taylor et al. (2003) explore cinder cone morphology as related to the age of the cinder cone and indicate that two distinct ages of cinder cones exist at
Newberry Volcano, and that the cinder cones are aligned parallel to regional faults. The two distinct ages of cinder cones may provide additional evidence of timing of regional
21 faulting events, assuming faulting on Tumalo and Sisters Fault Zones faults coincides
with eruptive processes at Newberry Volcano. Other authors have explored the relation of
Northwest Rift Zone faults and volcanic processes of northwestern Newberry Volcano
(Jensen and Chitwood, 2000; Jensen, 2000; Donnelly-Nolan et al., 2000).
There are multiple named and unnamed Tertiary and Quaternary cinder cones
along study area faults (Plate 1, Figure 9). Based on the location of volcanic features on
and next to area faults, I believe that Tumalo and Sister Fault Zones faults provided
pathways for magma migration to the surface in the past, and that the presence of aligned
Tertiary cinder cones indicates that faults have been present in the area since at least the
Tertiary period (Plate 1, Figure 10).
A volcanic outcrop containing scoria and obsidian occurs on the Tumalo Fault
between the Southern Columbia canal and Tumalo Reservoir. The presence of the
volcanic debris is additional evidence of the relation of faults and magma migration;
however, this type of outcrop was not observed at any other location in the field area.
Bend area faults are associated with several Quaternary cinder cones. Notable cones lying on or next to Bend area faults include Awbrey Butte, Pilot Butte, Coyote
Butte and Horse Butte. Southern portions of Bend area faults B2 and B4 (Photographs 4, and 9, respectively) exhibit displacements that may be considered inconsistent relative to the mapped length of the surface rupture. Displacements are approximately 20 m and 15 m for faults B2 (mapped length of 21 km) and B4 (mapped length of 19.2 km), respectively. According to a relation derived by Wells and Coppersmith (1994) for comparison of surface rupture length to average displacement, vertical displacements of
22 less than 0.5 m are probable for faults with lengths of approximately 20 km; the length of
fault T1 (approximately 36 km), the fault with the longest mapped length of all study area
faults, corresponds to surface displacement values near 0.7 m in Wells and Coppersmith
(1994) calculations. Subsurface volcanic activity such as magma migration or dike
emplacement along faults resulting in surface displacement may account for a portion of
total fault offset.
Evidence of Fault Timing
The following discussion on the time frame for displacement of glacial-fluvial sediments, lava flows, and pyroclastic deposits by faults of the Tumalo and Sisters Fault zones is based on data contained in Table 2; these data are based on aerial photograph interpretation and field confirmation where available. Deposits are discussed in order of increasing age; ages were determined from available literature.
Except for outwash deposits around Sisters (Plate 1), deposits in the northern portion of the study area are generally older than deposits in the southern portion of the study area near Bend. Surface displacement of younger rocks near Bend tends to be greater than that of older northern study area rocks, suggesting that faults in the southern study area have been more frequently and more recently active than northern study area faults.
Each fault does not necessarily come into contact with deposits of each type, for instance, glacial till and outwash of the Suttle Lake advance (Qgs/Qos) (Plate 1) only intercepts faults of the northern end of the Tumalo Fault Zone (faults T5, T13 and T14).
23 A similar relation exists for many study area faults and deposits. Please refer to Table 2 for a tabular representation of the interaction of faults and deposits of the study area.
Quaternary alluvium (Qal) – modern age, unfaulted, buries multiple fault segments.
Mazama Ash – 6,845 ± 50 14C years (Bacon, 1983), unfaulted, buries all faults
(Photograph 9).
Quaternary till and outwash of the Suttle Lake advance (Qgs/Qos) (Stage 2 age deposits approximately 10,000 to 20,000 years old (Sherrod et al., 2004)), unfaulted, buries portions of faults T5, T13, and T14 around the town of Sisters (Table 2).
Quaternary basalt of Newberry Volcano (Qbn) - multiple flows dated between
39,000 and 200,000 years (Sherrod et al., 2004, Donnelly-Nolan et al., 2000), are displaced by Bend area faults B1 through B4 (Photographs 10 and 11), Tumalo Fault
Zone faults T18, T19 and T20, and Northwest Rift Zone faults NWR5 and NWR6 (Table
2).
Quaternary sand (Qs) – estimated to be Stage 6 age deposits (approximately
140,000 years (Sherrod et al., 2004)), is faulted by Sisters Fault Zone faults S1 through
S9, S16, S18, S21 and S22, is faulted by Tumalo Fault Zone faults T1 (Photograph 12) through T4, T6 through T8, T10 and T16, and buries Bend area faults B3 and B4. Bend area Qs deposits stratigraphically overlie Qbn flows, and are therefore likely younger than Stage 6 (Table 2).
24 Quaternary Shevlin Park Tuff (Qsp) – dated at 170,000 and 270,000 years
(Sherrod et al., 2004), is faulted by Tumalo Fault Zone faults T1 through T6, T10, and
T19 (Table 2).
Quaternary basaltic andesite of Pilot Butte (Qbapb) – dated at approximately
180,000 years (Sherrod et al., 2004), is faulted by Bend area fault B3 (Photograph 13)
(Table 2).
Quaternary Tumalo Tuff (Qtt) – dated at approximately 400,000 years (Sherrod et al., 2004), is faulted by Sisters Fault Zone faults S1, S5, S8, S9, S10 and S21, is faulted by Tumalo Fault Zone faults T1, T2, T4, T6 and T19, and by Northwest Rift Zone fault
NWR9 (Table 2).
Quaternary basalt of Plainview – age estimated to be less than 600,000 years
(Sherrod et al., 2004), is faulted by Sisters Fault Zone faults S1, S4, and S16, and by
Tumalo Fault Zone faults T1, T5 and T8 (Table 2).
Quaternary Desert Springs Tuff (Qds) – dated at 600,000 years (Sherrod et al.,
2004), is faulted by Sisters Fault Zone faults S1, S3, S4, and S10, and by Tumalo Fault
Zone fault T1 (Table 2).
Quaternary basaltic andesite (Qba) – less than 780,000 years (Sherrod et al.,
2004), a Klawhop Butte flow south of Bend has been dated at approximately 39,000 years (Donnelly – Nolan et al., 2000), is faulted by Tumalo Fault Zone faults T1, T4, T5,
T8, and T20; Bend area fault B4 is buried by the Klawhop Butte flow.
Tertiary Deschutes Formation – youngest flows dated at more than 3.2 million years (McDannel, 1989), is faulted by Sisters Fault Zone faults S1 through S9, S11
25 through S20, S23 and S24 (Photograph 14), is faulted by Tumalo Fault Zone faults T1,
T5, T7 through T9, T11 through T16, T21 and T22, and by Bend area fault B4.
Evidence of Fault Reactivation
Evidence, such as differential displacement of deposits of different ages, is present along multiple study area faults, suggesting reactivation of some faults over time.
Multiple fault strands exhibit different amounts of vertical surface separation in deposits of different ages along a single fault trace, with older rock units generally exhibiting greater amounts of vertical surface separation (Table 2). Examples of differential displacement occur along fault T1 at the Columbia Southern Canal crossing as well as along faults of the Sisters fault zone near the town of Tumalo and near Pilot Butte in
Bend. A trench was excavated across the scarp of fault S3 at Rudi Road north of the town of Tumalo (Figure 5 inset). Fault data and stratigraphy revealed in the trench were logged by Mark Hemphill-Haley (1994) (Figure 11). I believe that evidence of multiple surface rupture events was revealed by Hemphill-Haley’s trench investigation, as stratigraphically deeper and older soil deposits are displaced more than overlying deposits.
Qs and Qsp deposits on either side of fault T1 are vertically separated by approximately 6 and 11 m, respectively, near the intersection of the Columbia Southern
Canal and T1 (T.17S, R.11E, Section 10 and 15, Shevlin Park 7.5 minute USGS quadrangle), indicating reactivation of T1 over time.
26 Different amounts of vertical surface separation are present in Td and Qs deposits along individual fault trends, indicating reactivation of Sisters fault zone faults over time.
Sisters fault zone faults S2, S3, S4, S5, and S6 displace both Td and Qs deposits northeast of the town of Tumalo (Plate 1); each of these faults displaces Td deposits by several meters more than displacement in Qs deposits.
A roadcut exposure of fault S10 demonstrates that not all study area faults reactivate or exhibit multiple surface rupture events; in this roadcut, vertically displaced
Qtt deposits are blanketed by undisturbed Qs deposits (Photograph 8); this also suggests that not all study area faults may have been identified at the surface.
Bend area fault B3 displaces 188 ka Qbapb flows and Qbn flows by differing amounts on the northeastern side of Pilot Butte, suggesting multiple surface rupture events over long periods of time.
Cumulative vertical displacement across the fault zones was reported by
Geomatrix Consultants (1995) to be less than 20 m. Structural cross-sections included with Plate 2 indicate little cumulative vertical displacement across the combined fault zones in the northern portion of the field area and appear to confirm the estimate provided in the Geomatrix Consultants (1995) report. A lack of laterally displaced stratigraphic markers or other evidence of lateral displacement precludes estimation of the cumulative lateral displacement.
DISCUSSION
The age of displaced deposits suggests that faults in the southern portion of the study area have been active more recently than segments in the central and northern portion of the study area, and displacements tend to be greater in the southern portion of the study area, especially near the northern flank of Newberry Volcano.
Comparison of observed surface displacement values between faults in the southern (i.e. Bend), central (Tumalo), and northern (Sisters/Redmond) portions of the field area indicates that a greater surface separation occurs on faults south of Bend than on faults near Tumalo and Sisters fault zones. Greater displacement occurs in younger deposits on the northern flanks of Newberry Volcano. Proximity of southern study area faults to Newberry Volcano, correlation of cinder cone alignment to fault segments, disproportionate surface displacement relative to fault length, and the likelihood of frequent and recent surface displacement is interpreted as supporting subsurface volcanic processes contributing to surface deformation near Bend.
Though study area faults are expressed as normal faults at the surface they do not exhibit features typical of normal faulting over long periods of time, or features consistent with Oregon Basin and Range faulting features as described by Donath (1962).
Large regional normal faults such as Green Ridge, basin-bounding faults near Summer
Lake, and the Walker Rim fault complex, including the Chemult Graben, are regional examples considered typical of normal faulting over time. The magnitude of surface
27 28 displacement differs significantly between study area faults and the above examples.
Study area faults generally exhibit several meters to tens of meters of vertical surface
separation on individual lineaments, and cumulative vertical surface separation across the
zones is likely less than 20 m (Geomatrix Consultants, 1995). Green Ridge, Summer
Lake and Walker Rim fault zones have cumulative vertical displacements in the range of
hundreds of meters (Donath, 1962). Deformation within the study area has been
distributed over multiple faults in a broad zone as opposed to one or several well-defined
faults in the Summer Lake basin or at Abert Rim.
With several exceptions, including portions of the Deschutes River and Squaw
Creek, I interpret the locations and directions of streams flowing from the eastern
Cascade Range slopes, such as Tumalo Creek and several unnamed creeks to the north, to
be a result of volcanic and glacio-fluvial processes rather than tectonic modification.
Review of several of the smaller study area streams reveals that the streams are typically bounded by volcanic flows (Plate 1). I interpret the location of the volcanic flows as occupying the topographic low points of the streambeds, forcing the streams to occupy positions alongside the flows. Multiple flows have elongated and lobate forms as they emanate from the Cascade Range. I did not observe evidence of lateral displacement of stream courses by faulting. In the instances where faults and stream courses interact at high angles (i.e. nearly perpendicular), the stream course appear to be impacted more by lava flow resistance to erosion, and the streams flow preferentially through the least resistant rock type.
29 Surface features which are inconsistent with typical examples of regional long- term normal faulting, a lack of evidence of lateral displacement across faults, and correlation of study area fault segments to cinder cone distribution suggests that magma migration plays a role in accommodation of local extensional forces and surface deformation.
SUMMARY AND CONCLUSIONS
Through performance of aerial photograph and GIS data interpretation and field inspection, 61 north-northwest trending normal faults were identified and characterized in central and northern Deschutes County. Study area faults were placed into three regional fault zones that comprise the study area, the Sisters, Tumalo Fault Zones and the
Northwest Rift Zone.
Study area faults displace late Pleistocene deposits, and evidence was found indicating the presence of faults during Td deposition. The youngest known displaced deposit is the 39 ka Klawhop Butte flow (faulted by T19), and the age of the oldest undisturbed deposit is the approximately 7,000-year-old Mazama ash. Faults displacing deposits of different ages by different amounts indicate multiple surface rupture events on several study area faults over time. Studies indicate a strong correlation between the locations of volcanic vents and faults.
30
ADDITIONAL GEOLOGIC QUESTIONS AND STUDY OPPORTUNITIES
Several issues remain with regard to understanding the tectonic and volcanic forces at work in the Bend-Sisters-Redmond area. Petrologic studies refining identification and age dating of volcanic flows on the north and northwestern flanks of
Newberry Volcano will lead to a better understanding of the timing and number of events on Bend area faults. Trenches spanning fault traces in Quaternary sands and gravels along Sisters Fault Zone and Tumalo Fault Zone faults may yield additional data for constraining the timing of events along several study area faults.
31
TABLES
32 33 Table 1
FAULT CHARACTERISTICS Dip Fault Strike Mapped Direction (kilometers) Fault Length Identification Notes S1 W N20ºW 12.0 western SFZ boundary at Laidlaw Butte S2 E N22ºW 6.4 eastern side of Smokey Butte S3 E N27ºW 14.5 Rudi Road trench fault, forms graben with S4 S4 W N25ºW 24.7 forms graben with S3 and horst with S5 S5 W N25ºW 33.1 forms with horst with S4 S6 W N23ºW 14.4 S7 W N16ºW 9.2 easternmost SFZ fault S8 E N29ºW 1.9 S9 W N15ºW 9.4 inferred south of Deschutes River S10 E N19ºW 0.7 scarp exposed in Tumalo Reservoir Road borrow pit S11 E N28ºW 2.4 north of Cline Falls Highway S12 W N36ºW 8.1 S13 E N42ºW 3.0 northeastern SFZ boundary S14 E N44ºW 2.3 north of Highway 126 S15 W N33ºW 4.1 S16 W N22ºW 13.8 Photograph 14 S17 Sisters Fault Zone Fault Sisters W N20ºW 2.6 S18 E N27ºW 2.8 McKenzie Canyon Reservoir north of Highway 126 S19 E N26ºW 1.7 S20 WN1ºE0.4 S21 W N14ºW 0.9 S22 E N38ºW 0.8 between S5 and S9 S23 E N26ºW 1.8 forms horst with S9 to west S24 E N37ºW 0.6 east of S12 S25 E N41ºW 1.6 east of S5 S26 W N28ºW 1.1 east of S5 S27 W N36ºW 2.3 S28 E N233ºW 2.0 B1 W N28ºW 4.8 Horse Butte to Knott Landfill, eastern margin of Knott Graben B2 W N25ºW 21.0 left steps in strike at outcrop scale
faults B3 E N26ºW 10.3 Pilot Butte area fault
Bend area Bend area B4 E N26ºW 19.2 Coyote Butte to Aubrey Butte, western margin of Knott Graben T1 W N22ºW 36.1 Tumalo Fault, not recognized north of Highway 126. T2 E N21ºW 5.2 located between faults T1 and T4 T3 W N24ºW 0.3 located west of T4 T4 E N25ºW 10.2 westernmost TFZ fault T5 W N31ºW 12.0 short antithetic graben forming fault north of Less Flat T6 E N22ºW 3.5 between T1 and T4 south of Bull Flat T7 E N11ºW 24.9 horsetail splay from T1 north of Tumalo Reservoir T8 W N10ºW 12.9 located between faults T1 and T7 T9 E N25ºW 3.2 inferred fault parallel to T1 at Bull Flat T10 W N15ºW 0.4 west of T3 T11 W N23ºW 4.2 T12 W N18ºW 3.3 west of T7 T13 W N19ºW 8.3 western McKinney Butte
Tumalo Fault Zone T14 W N17ºW 4.3 east of T13 T15 W N16ºW 6.8 east of T14 T16 W N24ºW 0.9 north of Highway 126 at Camp Polk Road near Cloverdale T17 E N23ºW 1.0 T18 E N36ºW 7.6 southwesternmost TFZ fault T19 E N22ºW 11.8 southern portion of Tumalo Fault, Photograph 2. T20 W N22ºW 7.3 displaces 39ka Klawhop Butte Qba flow. T21 W N17ºW 3.1 NWR1 W N26ºW 6.8 NWR2 E N17ºW 0.9 NWR4 W N12ºW 1.3 NWR5 E N31ºW 2.0 NWR6 W N31ºW 1.0 Rift Zone Northwest NWR7 E N31ºW 2.8 NWR8 W N25ºW 8.1 NWR9 E N37ºW 0.6
34
Table 2 Plainview Formation andesite of outwash of Quaternary Quaternary Quaternary Tumalo Tuff Mazama Ash Quaternary sand Shevlin Park Tuff Quaternary till and Tertiary Deschutes Newberry Volcano Quaternary basaltic Quaternary basaltic Desert Springs Tuff Quaternary andesite Deposit Description Suttle Lake advance Quaternary basalt of Quaternary basalt of Quaternary basalt of Quaternary allluvium undiffereniated origin andesite of Pilot Butte undifferentiated origin Map not Qal Qgs/ Qos Qa Qb Qbn Qs Qsp Qbapb Qtt Qbpp Qds Qba Td Designation mapped
Fault ID (140 ka) (140 Holocene Holocene Holocene 39 to 200 ka 39 to 170 - 270 ka 170 - (10 to 20 ka) to (10 Deposit Age less than 600 ka than less Greater than 3.2 Ma than Greater Approximately 188 ka Approximately 400 ka Approximately 600 ka Approximately Pleistocene / Holocene / Pleistocene Holocene / Pleistocene Oxygen Isotope Stage 2 Stage Oxygen Isotope Oxygen Isotope Stage 6 Stage Oxygen Isotope Overlies Qds, therefore, Qds, therefore, Overlies (approximately 8,000 ka) (approximately (generally less than 780 ka, than less (generally Potentially Holocene, Pleistocene Pleistocene Holocene, Potentially Klawhop Butte flow approx. 39 ka) approx. flow Butte Klawhop S1 Buried Buried 1.5 UD 4 UD UD S2 Buried Buried 1.5 UD S3 Buried Buried 2 UD 5 S4 Buried Buried 3 6 6 UD S5 Buried Buried 3 INF UD S6 Buried Buried <1 UD S7 Buried Buried UD UD S8 Buried Buried INF 1 UD UD S9 Buried Buried <1 UD 5 S10 Buried Buried Buried 6 6 S11 Buried Buried UD S12 Buried Buried UD S13 Buried Buried UD S14 Buried Buried UD S15 Buried Buried UD S16 Buried Buried Buried 2 UD S17 Buried Buried UD S18 Buried Buried INF UD S19 Buried Buried UD S20 Buried Buried UD S21 Buried Buried 1.5 S22 Buried Buried UD S23 Buried Buried UD S24 Buried Buried UD S25 UD S26 UD S27 UD S28 UD B1 Buried 2-12 B2 Buried 20 B3 Buried 2 Buried 10 B4 Buried Buried 2-12 Buried Buried UD
Notes: 5 = approximate observed vertical separation of deposit surface in meters. INF = Fault is inferred in deposit. UD = Fault displaces deposit by an undetermined amount. = Fault does not encounter deposit. Buried = Fault is buried by deposit. Reference: Sherrod, et al., (2004)
35
Table 2 Plainview Quaternary Quaternary Quaternary Tumalo Tuff Mazama Ash of Pilot Butte Quaternary sand Shevlin Park Tuff Newberry Volcano Newberry Desert Springs Tuff Quaternary andesite Deposit Description Suttle Lake advance Quaternary basalt of Quaternary basalt of Quaternary basalt of Quaternary allluvium undiffereniated origin of undifferentiated origin Quaternary basaltic andesite Quaternary basaltic andesite Tertiary Deschutes Formation Quaternary till and outwash of Map not Qal Qgs/ Qos Qa Qb Qbn Qs Qsp Qbapb Qtt Qbpp Qds Qba Td Designation mapped
Fault ID (140 ka) Holocene Holocene 39 to 200 ka 39 to 170 - 270 ka (10 to 20 ka) (10 to Deposit Age Deposit less than 600 ka than less Greater than 3.2 Ma Approximately 188 ka Approximately 400 ka Approximately 600 ka Approximately Pleistocene / Holocene Pleistocene / Holocene Oxygen Isotope Stage 2 Stage Isotope Oxygen Oxygen Isotope Stage 6 Stage Isotope Oxygen Overlies Qds, therefore, (approximately 8,000 ka) (approximately (generally less than 780 ka, than less (generally Potentially Holocene, Pleistocene Klawhop Butte flow approx. 39 ka) flow Butte Klawhop T1 Buried Buried 6 11 UD INF UD 4 UD T2 Buried Buried 3 INF INF INF T3 INF T4 Buried Buried UD UD 5 5 INF UD T5 Buried Buried Buried 7 INF INF 7 UD T6 Buried UD UD UD UD UD T7 Buried Buried 3 2 UD T8 Buried INF INF INF UD T9 Buried 1.5 T10 Buried INF INF INF T12 Buried INF T13 Buried Buried Buried UD T14 Buried Buried INF INF T15 Buried UD T16 Buried Buried INF INF T17 Buried UD T18 Buried UD T19 Buried Buried 4 - 20 UD 7 T20 Buried 2 - 5 2 - 5 T21 Buried UD T22 Buried UD NWR1 Buried UD NWR2 Buried UD NWR4 Buried UD NWR5 Buried UD NWR6 Buried UD NWR7 Buried UD NWR9 Buried UD Notes: 5 = approximate observed vertical separation of deposit surface in meters. INF = Fault is inferred in deposit. UD = Fault displaces deposit by an undetermined amount. = Fault does not encounter deposit. Buried = Fault is buried by deposit. Reference: Sherrod et al., (2004)
FIGURES
36 37
38
39
Figure 3
Correlation of Rock Units Sedimentary Volcanic Millions of Years Qal
Mazama 6,845+/-50 C14years B.P. Ash (Bacon, 1983)
Holocene ? 0.01 Qgs/Qos Qbn Qgj/Qoj Qa Qb
Quaternary Qba Qbapb ? Qsp
Cenozoic Qtt ?
Pleistocene Qbpp Qds 0.780
1.6 Tertiary
Pliocene Td 5.3
Correlation of Rock Units adapted from Sherrod et al., (2004)
Bacon, (1983)
40
41
42
43
44
45
46
47
Figure 11
PHOTOGRAPHS
48 49
Photo 1 Fault T7 in Quaternary sand at southeastern corner of the intersection of Highway 126 and Cloverdale Road. The photograph is oriented looking southeast roughly parallel to strike. Highway 126 is in the foreground. Arrows point to ground surface on the up-thrown (western) side of the fault and at the base of the fence on the down-dropped (eastern) side of the fault; vertical relief between the arrow points is approximately 1.5 meters.
Photo 2 Fault T19 in Quaternary basalt flows of Newberry Volcano in southern Bend; three-story house built on up-thrown side for scale. Photograph is oriented looking south, obliquely to strike. Approximate location of scarp is highlighted.
50
Photo 3 Fault S6 in Tertiary Deschutes Formation lava flows parallel to Barr Road, north of Tumalo. Photograph is oriented looking east, perpendicularly to strike, author for scale. Approximate location of scarp is highlighted.
Photo 4 Fault B2 in Quaternary basalt of Newberry Volcano, south of Bend near Horse Butte. Photograph is oriented looking southeast, obliquely to strike. Two-story houses for scale on the up-thrown (eastern) side of the fault. Approximate location of scarp is highlighted.
51
Photo 5 Fracture in Quaternary Tumalo Tuff with fracture fill from the overlying gravel deposit along the Tumalo Fault (T1). Photograph was taken near Tumalo Reservoir in a borrow pit dug into the up-thrown (eastern) side of the fault. The orientation of the photograph is to the northwest roughly perpendicular strike of T1. Twelve-ounce can for scale. Fracture surfaces and approximate boundary between Tumalo Tuff and the overlying gravel deposit with reworked (?) Tumalo Tuff are indicated. White silica cementation coats the fracture surfaces.
52
Photo 6 Silica-lined fracture in up-thrown (western) side of fault T7 at Cloverdale and Highway 126. The exposure is a borrow pit dug into the fault scarp in Quaternary sand (Qs). The photograph is oriented roughly perpendicular to the fault scarp, facing west. The wallet for scale is approximately 8-centimeters along the long axis.
53
Photo 7 Vertical fractures in Quaternary Shevlin Park Tuff (Qsp) in Anderson pit in Bend. Photograph is oriented looking northwest roughly perpendicular strike of fault T19. A loader is in the background for scale.
54
Photo 8 Fault S10 in Quaternary Tumalo Tuff exposed in a borrow pit parallel to Tumalo Market Road. Photograph is oriented looking west, obliquely to strike. Arrows point to air-fall portion of the deposit sandwiched between the upper Bend Pumice and lower Tumalo Tuff portions of the deposit. People for scale. Vertical displacement of the air-fall portion is approximately 6 meters; the overlying Quaternary sand deposit is unfaulted. Offset of the deposit occurs along vertical fracture planes that now appear as negative relief features in the outcrop.
55
Photo 9 Fault T19 in Quaternary Tumalo Tuff at Anderson Pit in Bend. Vertical fractures are present in the down-dropped (eastern) side of the fault, which is buried by reworked Tumalo Tuff. Undisturbed Mazama Ash overlies the fault. Horizontal striations present in the outcrops may be due to mining activities. The photograph is facing northwest and is oriented roughly parallel to strike. A 1-meter survey staff is present for scale.
Photo 10 Fault B4 in Quaternary basalt of Newberry Volcano south of Knott Landfill in southern Bend. Fault is highlighted, and the arrow points to the roof of a barn on the up-thrown (western) side of the fault. Photograph is oriented looking south, obliquely to strike. Approximate location of scarp is highlighted.
56
Photo 11 Fault B4 transects Highway 20 in central Bend, with cars for scale. White car is on the up-thrown (western) side of the fault. The photograph is oriented looking west, roughly perpendicular to strike. Approximate location of scarp is highlighted.
Photo 12 Fault T1, the Tumalo Fault, in Quaternary sand and Tertiary Deschutes Formation lava flows at Bull Flat. Approximate location of the scarp is highlighted. The photograph is oriented looking south obliquely to strike. Relief from Bull Flat to the top of the ridge is approximately 90 meters. Approximate location of scarp is highlighted.
57
Photo 13 Fault B3 in Quaternary andesitic basalt of Pilot Butte, northeast of Pilot Butte in Bend. The photograph is oriented looking southwest, roughly perpendicular to strike. The Ronald McDonald House is in the foreground, and a two-story house sits upon the up-thrown (western) side of the fault.
Photo 14 Fault S16 in Tertiary Deschutes formation pyroclastic flow deposits and lava flows. Photograph is of the Highway 126 roadcut on the western side of Deep Canyon and is oriented looking northwest perpendicularly to strike. The contact between pyroclastic deposits and the overlying lava flow is highlighted along with the base of a white section of the pyroclastic deposit. Highway 126 is in the foreground. The distance between the points of the arrows is approximately 4 meters.
REFERENCES
Bacon, C.R., 1983, Eruptive history of Mount Mazama and Crater Lake caldera, Cascade Range, USA: Journal of Volcanology and Geothermal Research, v. 18, p. 57-118.
Blackwelder, E. 1948, The Great Basin, with emphasis on glacial and postglacial times. Bulletin of Univ. of Utah, v. 38, no. 20, 191 p.
Champion, D.E., Donnelly-Nolan, J.M., and Lanphere, M.A., 2002, Mapping Newberry Volcano’s Extensive North Flank Basalts. Geological Society of America Cordilleran Section – 98th Annual Meeting.
Chitwood, L.A., 2002, personal communication, re: presence of Mazama ash.
Cole, J.W., Darby, D. J. & Stern, T.A. 1995, Taupo Volcanic Zone and Central Volcanic Region back-arc structures of the North Island, New Zealand. In: Back-arc Basins: Tectonics and Magmatism, B. Taylor (editor), Plenum, New York: 1-24.
Conrey, R.M., 1985, Volcanic stratigraphy of the Deschutes Formation, Green Ridge to Fly Creek, north-central Oregon: Corvallis, Oregon State University, M.S. thesis, 328 p.
Cox, A., Doell, R. R., and Dalrymple, G. B., 1965, Quaternary of the United States, edit. by Wright, H. E., jun., and Frey, D. G., 817–830 (Princeton University Press).
Dalrymple, G. B. and Lanphere, M A., 1969, Potassium-argon dating; principles, techniques, and applications to geochronology: W. H. Freeman, San Francisco, Calif., 258 p.
Dicken, A.P., 1995, Radiogenic Isotope Geology. Cambridge University Press, New York, N.Y., 452 p.
Donath, F.A., 1962, Analysis of basin-range structure, south-central Oregon, Geological Society of America Bulletin, v.73, p. 1-16.
Donnelly – Nolan, J.M., 2003, personal communication, re: age of Newberry volcanic deposits.
58 59
Donnelly - Nolan, J.M., Champion, D.E., and Lanphere, M.A., 2000, North Flank Stratigraphy Revealed by New Work at Newberry Volcano, in Jensen, R. A. and Chitwood, L.A., eds, What’s New at Newberry Volcano, Oregon, Guidebook for the Friends of the Pleistocene Eight Annual Pacific Northwest Cell Field Trip, pp. 177-180.
Eaton, G., 1979, Regional geophysics, Cenozoic tectonics and geological resources of the Basin and Range province and adjoining regions, in Newman, G.W., and Goode, H.D., eds., Basin and Range Symposium: Denver, Colorado, Rocky Mountain Association of Geologists. p. 11-39.
Faure, G., 1986, "The K-Ar method of dating", in Principles of Isotope Geology, second edition, John Wiley and Sons, New York, N.Y., pp. 66-92.
Geomatrix Consultants, 1995, Seismic Design Mapping, State of Oregon, Oregon Department of Transportation, Salem Oregon. 252 p.
Hemphill-Haley, M.A., 1994, Stratigraphic Cross-section from the Rudi Road Fault trench, Figure 12 (unpub.)
Hoefs, J., 1980, Stable Isotope Geochemistry. Springer-Verlag, Berlin; New York. 208 p.
Hunt, C. B., 1979, The Great Basin, an overview and hypotheses of its origin, in Newman, G. W., and Good, H. D., eds., Basin and Range Symposium: Rocky Mountain Association of Geologists and Utah Geological Association, p. 1–9.
Irving, E, 1964, Paleomagnetism and its application to geological and geophysical problems. John Wiley and Sons, New York, N.Y., pp. 399.
Jensen, R.A., and Chitwood, L. A. 2000, What’s New at Newberry Volcano, Oregon: Guidebook for the Friends of the Pleistocene Eighth Annual Pacific Northwest Cell Field Trip, 190 p.
Jensen, R.A., 2000, Roadside Guide to the Geology of Newberry Volcano, Third Edition, CenOreGeoPub, Bend, Ore. 168 p.
Lawrence, R.D., 1976, Strike-slip faulting terminates the Basin and Range province in Oregon: Geological Society of America Bulletin, v.87, p. 846-850.
MacLeod, N.S., Sherrod, D.R., Chitwood, L.A., Jensen, R.A., 1995, Geologic Map of Newberry Volcano, Deschutes, Klamath, and Lake Counties, Oregon: U.S. Geological Survey Miscellaneaous Investigation Map I-2455, scale 1:62,500 and 1:24,000.
60
McDannel, A.K., 1989, Geology of the southernmost Deschutes basin, Tumalo quadrangle: Corvallis, Oregon State University, M.S. thesis, (unpub.) 166 p.
Mimura, Koji, 1992, Reconnaissance Geologic Map of the West Half of the Bend and the East Half of the Shevlin Park 7.5' Quadrangles, Deschutes County, Oregon: U.S. Geological Survey Miscellaneous Field Studies Map MF-2189, scale 1:24,000.
Mix, A.C., 1992, The marine oxygen-isotope record: Constraints on timing and extent of ice growth events (120–65 ka). In: Clark, P.U., Lea, P.D., (Eds.), The Last Interglacial–Glacial Transition in North America. Boulder, CO. Geological Society of America Special Paper 270, 19–30.
Peterson, N.V., Groh, E.A., Taylor, E.M., and Stensland, D.E., 1976, Geology and mineral resources of Deschutes County, Oregon: Oregon Department Geology and Mineral Industries Bulletin 89, 66 p., 3 maps.
Pezzopane, S.K., 1993, Active Faults and Earthquake Ground Motions in Oregon, Ph D. dissertation, 208 pp. University of Oregon, Eugene, March 1993.
Pezzopane, S.K. and Weldon, R.J., 1993, Tectonic Role of Active Faulting in Central Oregon, Tectonics, Vol. 12, No. 5, pages 1140-1169, October, 1993.
Prothero, D. R., 1994, The Eocene-Oligocene transition: paradise lost. Columbia University Press, New York, 291p.
Priest, G.R., 1990, Volcanic and tectonic evolution of the Cascade Volcanic Arc, Central Oregon, Journal of Geophysical Research, Vol. 89, No. B12, Pages 19,583- 19,599, November, 1990.
Sherrod, D.R., Taylor, E.M., Ferns, M.L., Scott, W.E., Conrey, R.M., and Smith, G.A., 2004, Geologic Map of the Bend 30- X 60-Minute Quadrangle, Central Oregon. U.S. Geological Survey Geologic Investigation Series Map I-2683. Scale 1:100,000.
Stacey, F. D. and Banerjee, S. K., 1974, The Physical Principles of Rock Magnetism. Elsevier Scientific Pub. Co., Amsterdam, New York. 195 p.
Tarling, D.H., 1983, Paleomagnetism: Principles and Applications in Geology, Geophysics, and Archaeology. Chapman and Hall, London: New York. 379p.
61
Taylor, B., 1995, Back-arc basins: Tectonics and Magmatism: Plenum Press, New York, N.Y., 524p.
Taylor, E.M., 1981, Central High Cascade roadside geology, in Johnston, D.A., and Donnelly-Nolan, J.M., eds., Guides to some volcanic terranes in Washington, Idaho, Oregon, and northern California: U.S. Geological Survey Circular 838, p. 55-83.
Taylor, E.M., 1990, Volcanic History and Tectonic Development of the Central High Cascade Range, Oregon: Journal of Geophysical Research, Vol. 93, No, B12, Pages 19,611-19,622, November 10, 1990.
Taylor, E.M. and Ferns, M.L., 1994, Geology and Mineral Resource Map of the Tumalo Dam Quadrangle, Deschutes County, Oregon: Oregon Department of Geology and Mineral Industries, Geological Map Series GMS-81.
Taylor, S.B., Templeton, J.H., and Giles, D.E.L., 2003, Cinder Cone Morphometry and Volume Distribution at Newberry Volcano, Oregon: Implications for Age Relations and Structural Control on Eruptive Process. Geological Society of America Abstracts with Programs, Vol. 35, No. 6, September 2003, p. 421
Taylor, S.B., Templeton, J.H., Budnick, J., Drury, C., Fisher, J. and Runyan, S., 2005, Spatial Analysis of Cinder Cone Distribution at Newberry Volcano, Oregon: Implications for Structural Control on Eruptive Process. Geological Society of America Abstracts with Programs, Vol. 37, No. 7, September 2003, p. 431
Uyeda, S., Kanamori, H., 1979, Back-arc opening and mode of subduction. Journal of Geophysical Research, Vol. 84, Issue B3, p. 1049-1062.
Wells, D. L. and Coppersmith, K.J., 1994, Empirical relationships among magnitude, rupture length, rupture area and surface displacement. Bull. Seismol. Soc. Amer. 84, 974 – 1002.
Williams, D. F., Lerche, I., Full, W.E., 1988, Isotope chronostratigraphy: theory and methods: Academic Press, San Diego, Calif., 345p.
APPENDIX A - MAP REFERENCE
Maps, Digital Raster Graphics (DRGs) and Digital Elevation Models (DEMs) used during the course of this study include the following:
USGS 7.5-minute Quadrangle Maps, DRGs and DEMs (1:24,000 scale)
Bend Quadrangle Little Squaw Back Butte Quadrangle Bend Airport Quadrangle Shevlin Park Quadrangle Black Butte Quadrangle Sisters Quadrangle Black Crater Quadrangle Squaw Back Ridge Quadrangle Cline Falls Quadrangle Three Creek Butte Quadrangle Forked Horn Butte Quadrangle Tumalo Quadrangle Henkle Butte Quadrangle Tumalo Dam Quadrangle Horse Butte Quadrangle Tumalo Falls Quadrangle Lava Butte Quadrangle
USGS 30- by 60-minute Quadrangle Maps (1:100,000 scale) hard copy maps
Bend 30- by 60-minute Quadrangle Crescent 30- by 60-minute Quadrangle
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APPENDIX B - FAULT ZONE DESCRIPTIONS
Appendix B contains written descriptions of study area faults and includes information pertaining to fault identification, length, location, dip direction, strike, deposits displaced (including observed amounts if available), and other information collected during fieldwork. The written descriptions of study area faults primarily contain information presented in Tables 1 and 2.
Bend Area Faults
Fault B1 is an approximately 4.8 km long down-to-the-west normal fault that extends from east of Horse Butte to east of Knott Landfill. It has an average strike of
N28°W, and is fully constrained to Qbn flows. I observed a maximum scarp height of 12 m south of Knott Landfill; most observed scarps heights are approximately 2 m along the central and northern portion of the fault.
Fault B2, the easternmost Bend area fault, is an approximately 25 km down-to- the-west normal fault with a discontinuous surface expression. B2 has an average strike of N25°W and extends from southeast of Coyote Butte to approximately 3.6 km southeast of Tumalo State Park. Fault B2 is fully constrained to Qbn flows and exhibits left steps in trend on outcrop scale at several locations (Figure 6). At several locations along the strike of B2, vertical scarp heights diminish to zero and the fault is lost amongst hummocky volcanic flow topography. I observed fault B2 scarp heights exceeding 15 m
63 64 along the southernmost portion of the fault (Photograph 4). The maximum observed scarp height along the northern portion of fault B2 is approximately 2 m.
Fault B3 is an approximately 10.3 km down-to-the-east normal fault. It has an average strike of N26°W and extends from approximately 3 km southeast of Pilot Butte to 2 km south of Tumalo State Park. Late Pleistocene sand and aeolian deposits bury the southern portion of B3; the northern portion of B3 is difficult to trace into hummocky
Qbn flow deposits. I observed fault B3 scarp heights of approximately 10 and 2 m in
Qbapb (Photograph 13) and Qbn flows, respectively.
Fault B4 is an approximately 19.1 km down-to-the-east normal fault. It has an average strike of N26°W that extends from Coyote Butte’s northern base to northeastern
Awbrey Butte, traversing a large portion of the city of Bend. Coyote Butte does not appear to be faulted. Fault B4 forms a 15 m wide horst with an associated antithetic fault southwest of Horse Butte. Faults B4 and B1 bound either side of Knott Graben (Jensen and Chitwood, 2000).
Bend area faults tend to exhibit diminished scarp heights on the northern end of the faults relative to scarp heights observed on the southern portion of the faults. I observed scarp heights in excess of 15 m on fault B4 south of Knott Landfill (Photograph
10). North along strike of fault B4 scarp heights range between 2 and 5 m in Qbn flow deposits (Photograph 11). Scarp heights of about 4 m are typical along the central portion of B4. Actual vertical surface separation is difficult to ascertain in much of Bend due to urbanization. The location of Fault B4 is inferred north of the fault intersection with the
Deschutes River at Awbrey Butte’s eastern base.
65 Northwest Rift Zone
Fault NWR1 is an approximately 9.3 km down-to-the-west normal fault that extends from approximately 2 km west of Klawhop Butte to Green Mountain, is buried by young lava flows of Lava Butte (a 14C age of 6160 ± 65 years from charcoal found beneath cinders (Jensen and Chitwood, 2000)). It has an average strike of N26°W and displaces the easternmost portion of Green Mountain.
Fault NWR2 is an approximately 0.9-km down-to-the-east normal fault. It has an average strike of N17ºW and is west of the Deschutes River.
Fault NWR4 is an approximately 1.3-km down-to-the-west normal fault. It has an average strike of N12ºW and displaces northeastern Green Mountain.
Fault NWR5 is an approximately 2.0-km down-to-the-east normal fault. It has an average strike of N31ºW. NWR5 forms a narrow, shallow, and short graben with fault
NWR6.
Fault NWR6 is an approximately 1.0-km down-to-the-west normal fault. It has an average strike of N31ºW. Fault NWR6 forms a narrow, shallow, and short graben with
Fault NWR5.
Fault NWR7 is an approximately 2.8-km down-to-the-east normal fault. It has an average strike of N31ºW and is west of the Deschutes River.
Fault NWR8 is an approximately 8.1 km down-to-the-west normal fault that extends from northeast of Green Mountain to Tumalo Creek. It has an average strike of
66 N20°W and displaces Qbn and Qb flows by 3 to 4 m. Fault NWR8 shares a common trend and a similar amount of displacement as T4, but has a different dip direction.
Fault NWR9 is an approximately 0.60-km down-to-the-east normal fault. It has an average strike of N37ºW.
Sisters Fault Zone
Fault S1 is an approximately 12 km down-to-the-west normal fault with a discontinuous surface expression. S1 is the western-most fault of the Sisters fault zone; it has an average strike of N20ºW and extends northward from western Laidlaw Butte.
Fault S1 is the western boundary of Smokey Butte, and the northernmost segment is parallel to Tumalo Fault Zone fault T7. I observed scarp heights of approximately 1.5 m in Qs deposits and of approximately 4 m in Qbpp deposits.
Fault S2 is an approximately 6.4-km down-to-the-east normal fault that extends from eastern Laidlaw Butte to south of Innes Market Road. It has an average strike of
N22°W, and I observed scarp heights of approximately 1.5 m in Qs deposits, and believe that Tertiary Smokey Butte may be displaced down to the east by up to as much as 12 m.
Fault S3 is an approximately 14.5-km down-to-the-east normal fault that extends from approximately 1 km north of the town of Tumalo to Dry Canyon. It has an average strike of N27°W. Approximately 2 km north of the town of Tumalo (at Rudi Road) fault
S3 displays a left-step in strike, and has an associated antithetic fault with which it forms a small, well-defined graben that potentially serves as a depositional basin between faults
S3 and S4 during wetter climates. I observed scarp heights exceeding 1 m in Qs deposits
67 north of Tumalo, at the location of the Rudi Road trench site (Figure 5), and scarp heights in excess of 4 m in Td deposits several hundred meters north of the Rudi Road trench site. Mark Hemphill-Haley installed and logged the stratigraphy and fault traces in a trench across the scarp of fault S3. Figure 11 is an illustration of the trench wall, and shows multiple rupture events over time along this fault.
Fault S4 is an approximately 25 km down-to-the-west normal fault with a discontinuous surface expression that extends from the Deschutes River south to Fremont
Canyon. S4 forms a narrow horst with S5, a graben with S3. It has an average strike of
N25°W. I observed scarp heights of approximately 3 m in Qs deposits, scarp heights of less than 6 meters in Qbpp and Qds, and scarp heights of up to 18 m in Td deposits.
Fault S5 comprises several disconnected fault segments with a combined length totaling more than 33 km and it has an average strike of N23°W. All segments of S5 identified north of Innes Market Road are confined to Td flows. The southern segment of
S5 forms a narrow horst with S4 in Qs and Td south of Innes Market Road.
Fault S6 is an approximately 14.4 km discontinuous down-to-the-west normal fault that extends from west of Long Butte to approximately 5.5 km northwest of Cline
Buttes peak. S6 is a broadly arcuate fault trace concave to the southwest and forms a small graben with fault S11 on the western extent of Cline Buttes. I observed scarp heights of less than 1 m in Qs deposits north of the Deschutes River, with the fault surface expression becoming obscured north of Marsh Road. I observed S6 scarp heights of as much as 12 m in Tertiary basaltic andesite of Laidlaw Butte south of the Deschutes
River, and of more than 3 m in Td north of Cline Falls Highway.
68 Fault S7 is an approximately 9.2 km down-to-the-west normal fault stretching from western Long Butte to Cline Buttes. It has an average strike of N16ºW.
Fault S8 is an approximately 2 km down-to-the-east normal fault. It has an average strike of N29ºW and is situated west of Tumalo State Park. I observed scarp heights of approximately 1 m in Qs deposits.
Fault S9 is an approximately 9.4 km down-to-the-west normal fault that extends from west of Long Butte to southwest of Cline Buttes. It has an average strike of
N15°W, and is situated between S5 and S6. I observed scarp heights of approximately 1 m in Qs deposits northeast of Tumalo.
Fault S10 is an approximately 0.7 km down-to-the-east normal fault that extends from the Deschutes River at Tumalo State Park to a borrow pit excavated into Qtt and Qs deposits north of Tumalo Market Road (Photograph 8). It has an average strike of
N19ºW. I observed faulted deposits with displacement distributed across several fault scarps combining to equal approximately 6 m of vertical displacement in Qtt, and I observed a similar amount of offset in Qds deposits along the Deschutes River at Tumalo
State Park less than one km south.
Fault S11 is an approximately 2.4 km down-to-the-east normal fault. It has an average strike of N27°W and is fully constrained within Td flow deposits north of Cline
Falls Highway.
Fault S12 is an approximately 8.3 km down-to-the-west normal fault north of
Cline Falls Highway. It has an average strike of N36°W.
69 Fault S13 is an approximately 3 km down-to-the-east normal fault located near the confluence of Squaw Creek and Fremont Canyon. It has an average strike of N42°W.
Fault S14 is an approximately 2 km down-to-the-east normal fault. It has an average strike of N44°W and is north of Highway 126.
Fault S15 is a 4 km long down-to-the-west normal fault immediately west of S14.
It has an average strike of N33°W.
Fault S16 is an approximately 13.8 km long down-to-the-west normal fault with a discontinuous surface expression and an average strike of N22°W. A road cut at the intersection of Highway 126 with S16 reveals a multiple event fault scarp in Td deposits
(Photograph 14). Td vesicular basalt is approximately 5 m-thick over the hanging wall and up against a pre-existing scarp. Tertiary flows have been faulted at least once since deposition. The pre-basalt hanging wall has been faulted out of the exposure, and the uppermost basalt layer has been displaced approximately 3 m. This indicates that faulting of Td occurred prior to and after emplacement of the 3.4 Ma vesicular basalt flow, indicating fault activity during the Miocene. S16 and accompanying splays also displace mid-Pleistocene Qbpp in Deep Canyon by approximately 2 m, indicating fault reactivation over time.
Fault S17 is an approximately 2.6 km down-to-the-west normal fault. It has an average strike of N20°W and is confined to Td.
Fault S18 is an approximately 2.8 km down-to-the-east normal fault. It has an average strike of N27°W and is located north of Highway 126 near McKenzie Canyon
Reservoir.
70 Fault S19 is an approximately 1.7 km down-to-the-east normal fault. It has an average strike of N26°W and is east of S18.
Fault S20 is an approximately 0.4 km down-to-the-west normal fault with a north- south strike that displaces a Tertiary cinder cone west of Barr Road.
Fault S21 is an approximately 0.85 km down-to-the-west normal fault that has an average strike of N14°W and is near the junction of Tumalo Reservoir Road and Tumalo
Market Road. I observed scarp heights of approximately 1.5 m in Qs deposits.
Fault S22 is an approximately 0.80 km down-to-the-east normal fault. It has an average strike of N38°W and is situated between S5 and S9.
Fault S23 is an approximately 1.8 km down-to-the-east normal fault. It has an average strike of N25°W and forms a narrow horst with S9 to the west.
Fault S24 is an approximately 0.6 km down-to-the- east normal fault. It has an average strike of N37°W and is located north of Highway 126 and east of S12.
Fault S25 is an approximately 1.6 km down-to-the-east normal fault with an average strike of N41°W east of S5.
Fault S26, a 1.1 km down-to-the-west normal fault with a strike of N28°W, and is east of S5.
Fault S27, a 2.3 km down-to-the-west normal fault with an average strike of
N36°W is east of S5.
Fault S28, a 2.0 km down-to-the-east normal fault with an average strike of
N33°W is east of S5.
71 Tumalo Fault Zone
Fault T1 is an approximately 36 km long down-to-the-west normal fault that
extends from east of Sisters to west of Bend. It has an average strike of N23°W. I
observed scarp heights of approximately 6 m in Qs deposits near Tumalo Reservoir, and
approximately 11 m in Qsp near the Columbia Southern Canal intersection with T1. I did
not recognize T1 north of Highway 126.
Fault T2 is an approximately 5.3-km down-to-the-east inferred normal fault. It
has an average strike of N21ºW and lies between T1 and T4. I observed scarp heights of approximately 3 m in an undated Qb deposit; no displacement was observed in deposits of known age.
Fault T3 is an approximately 0.32 km down-to-the-west normal fault less than
1,000 meters west of T4. It has an average strike of N24ºW.
Fault T4 is an approximately 10.2 km long normal fault that is down-to-the-east that extends from western Bull Flat to Tumalo Creek. It has an average strike of N25°W.
I observed scarp heights of as much as 5 m in Qs deposits southwest of Bull Flat.
Fault T5 is an approximately 12 km down-to-the-west normal fault that extends from southern Less Flat to approximately 3 km south of Sisters. It has an average strike of N31°W. I observed scarp heights of approximately 0.7 m in Qs deposits, 2m in Qbpp deposits, 5 m in undated Qba deposits and 7 m in Qb flow deposits. A portion of T5 is accompanied by a short antithetic fault to form a narrow, well-defined graben north of
Less Flat.
72 Fault T6 is an approximately 3.5 km down-to-the-east normal fault situated between T1 and T4 south of Bull Flat. It has an average strike of N22°W.
Fault T7 is an approximately 25 km down-to-the-east normal fault that extends as a splay from fault T1 north of Tumalo Reservoir Road to east of Henkle Butte. It has an average strike of N11°W. I observed scarp heights of approximately 30 cm in Qs deposits east of Less Flat, and of approximately 3 m in Qs deposits near Cloverdale
(Photo 1); I also observed scarp heights of 2 m in Qbpp deposits.
Fault T8 is an approximately 13 km down-to-the-west normal fault between T1 and T7. It has an average strike of N10°W.
Fault T9 is an approximately 3.2 km down-to-the-east normal fault less than 300 m east of T1, and it is wholly constrained to Td lava flows. It has an average strike of
N25ºW and forms a short, narrow horst with T1.
Fault T10 is an approximately 0.4 km down-to-the-west normal fault less than
300 m west of T3. It has an average strike of N15ºW.
Fault T11 is a 4.2 km down-to-the-west fault north of Highway 126 and it has an average strike of N23°W.
Fault T12 is an approximately 3.3 km down-to-the-west normal fault, opposite a
Tertiary cinder cone chain from T7. It has an average strike of N18ºW.
Fault T13 is an approximately 8.3 km down-to-the-west normal fault situated on western McKinney Butte 1.5 km east of Sisters. It has an average strike of N19ºW.
Fault T14 is an approximately 4.3 km down-to-the-west normal fault. It has an average strike of N17ºW and is east of T13.
73 Fault T15 is an approximately 6.8 km down-to-the-west normal fault. It has an average strike of N16ºW is situated approximately 1.5 km east of T14.
Fault T16 is an approximately 0.88 km down-to-the-west normal fault. It has an average strike of N24ºW roughly paralleling Camp Polk Road.
Fault T17 is an approximately 1.0 km down-to-the-east normal fault. It has an average strike of N23ºW, is fully constrained to an undated Qb flow.
Fault T18 is an approximately 7.6 km down-to-the-east normal fault fully constrained to Qbn deposits and is between T19 and NWR6. It has an average strike of
N36ºW.
Fault T19 is an approximately 11.3 km long down-to-the-east normal fault that extends from southwestern Aubrey Butte to approximately 4 km northwest of Bessie
Butte. It has an average strike of N22°W. I observed scarp heights of approximately 15 m in Qbn deposits south of Bend (Photograph 2) and 7 m in Qtt deposits in Anderson Pit
(Photograph 9). The southern portion of T19 is buried by a 39 ka Qba flow originating from Klawhop Butte (Donnelly-Nolan et al., 2000). The Qsp exposure at Anderson Pit contains vertical fractures up to 60 cm wide extending to the top of the exposure
(Photograph 7). T19 displaces Qtt in Anderson Pit by approximately 7 m; the reworked
Qtt is well exposed in an excavation (Photograph 9). Displaced Qtt is capped by undisturbed Mazama ash.
Fault T20 is an approximately 7.3 km down-to-the-west fault that runs parallel to
China Hat Road south of Bend. T20 trends parallel to and forms a narrow horst with the
74 southernmost 6 km stretch of T19. It has an average strike of N22°W. I observed scarp heights of approximately 5 m in Qbn, and approximately 2 m in Qba south of Bend.
Fault T21 is a 3.1 km down-to-the-west fault that is located north of Highway 126 and it has an average strike of N17°W.