Quaternary reactivation of the Kern Canyon fault …tectonics.caltech.edu/publications/pdf/Nadin_GSA2010.pdf2010/05/20 · Nadin and Saleeby 1672 Geological Society of America Bulletin,

ABSTRACT

The Kern Canyon fault, the longest fault in the southern Sierra Nevada, is an active structure and has been reactivated at discrete times over the past ~100 m.y. in response to changing lithospheric stresses. After initiation as a Cretaceous transpressional structure, the Kern Canyon fault transitioned into a dextral strike-slip shear zone that remained active as it was exhumed into the brittle re-gime during regional Late Cretaceous uplift of the Sierra Nevada batholith. The Kern Canyon fault was reactivated during Miocene regional extension as part of a transfer zone between two differentially extending domains in the southern Sierra Nevada. Subsequent normal displacement along the fault began in Pliocene time. New evidence for fault activity, which continued into late Quaternary time, includes its current geomorphic expression as a series of meters-high, west-side-up scarps that crop out discontinuously along the fault’s 130-km length. Relocated focal mechanisms of modern earthquakes confirm ongoing normal faulting, and geodetic measure ments suggest that the Sierra Nevada is uplifting relative to the adjacent valleys. This evidence for recent activity overturns a long-held view that the Kern Canyon fault has been in active for more than 3.5 m.y. Its reactiva-tion indicates that deformation repeatedly localized along a pre existing crustal weak-ness, a Cretaceous shear zone. We propose that a system of inter related normal faults, including the Kern Canyon fault, is respond-ing to mantle lithosphere removal beneath the southern Sierra Nevada region. The loca-tion of the active Kern Canyon fault within the Sierra Nevada–Great Valley microplate indicates that deformation is occurring within the microplate.

INTRODUCTION

The Sierra Nevada batholith of California is one of the world’s largest batholiths, and was assembled by multiple intrusive events largely during Cretaceous time. The mountain range and westward-adjacent Great Valley, fi lled largely with sediments eroded from the batho-lith, together constitute a semi-rigid crustal block termed the Sierra Nevada microplate, whose velocity and rotation vectors differ from those of the rest of North America (Argus and Gordon, 1991; Dixon et al., 2000; Sella et al., 2002). This “microplate” is bounded to the west by the San Andreas transpressive plate junction. To the east are the Eastern Califor-nia Shear Zone and its northward continuation, the Walker Lane (Fig. 1), which together form the western boundary of the Basin and Range extensional province (e.g., Jones et al., 2004). Geodetic data show that the Eastern California Shear Zone–Walker Lane belt is undergoing dextral shear that accounts for ~20% of total relative motion between the North American and Pacifi c plates (Dokka and Travis, 1990; Thatcher et al., 1999; Dixon et al., 2000; Gans et al., 2000; Bennett et al., 2003; Oldow et al., 2008; Hammond and Thatcher, 2007).

Many studies have shown that there is active faulting in the eastern Sierra Nevada range front (recent selected references: Le et al., 2007; Surpless , 2008; Taylor et al., 2008). There have also been predictions of extensional defor-mation within the southern part of the Sierra Nevada batholith (Jones et al., 2004) and, more recently, evidence for uplift of the southern Sierra Nevada relative to the Owens Valley to the east (Fay et al., 2008; see Fig. 1 for location). This study presents the fi rst documentation of active extensional structures within the range that are consistent with the predicted uplift.

We defi ne the Kern Canyon fault system as an ~130-km-long zone of faulted basement, with several parallel, near-vertical fault strands that strike generally northward from the south-ern edge of the Sierra Nevada along the batho-lith’s long axis (Fig. 1). Latitude 35.7°N, at

the Isabella basin (Fig. 2), is a geographically signifi cant location for defi ning Kern Canyon fault geometry. South of the Isabella basin, the Kern Canyon fault has been interpreted to con-nect with the Breckenridge scarp and the White Wolf fault (Fig. 1; e.g., Ross, 1986). Across this northeast-striking segment of the fault zone, brittle deformation is localized along discrete fractures across an ~150-m-wide zone at the currently exposed surface. This segment devel-oped ca. 86 Ma as a plastic-to-brittle structure during exhumation of the southernmost part of the batholith (Nadin and Saleeby, 2008; Saleeby et al., 2009). North of the Isabella basin, brittle structures of the Kern Canyon fault overprint the proto–Kern Canyon fault (labeled PKCF in Fig. 1), a 2-km-wide zone of pervasively duc-tilely sheared igneous and metamorphic rocks. The proto–Kern Canyon fault was a transpres-sive structure that accommodated arc-normal shortening and dextral offset from 100 to 80 Ma (Nadin and Saleeby, 2008).

Part of the Kern Canyon fault system near the latitude of the Isabella basin was remobilized as an early to middle Miocene oblique-slip transfer zone between two extensional domains, one at the southernmost end of the San Joaquin basin and the other just east of the Isabella basin (see Fig. 2 for landmarks; see fi g. 8 of Mahéo et al., 2009, for extensional domains). The Brecken-ridge scarp and White Wolf fault segments of the Kern Canyon fault system lie between these extensional domains and are undergoing Qua-ternary offset, with the notable 1952 M = 7.3 Kern County earthquake attributed to the White Wolf fault. However, focal mechanisms along the Breckenridge scarp, the White Wolf fault, and the Kern Canyon fault segment north of the Isabella basin indicate substantially differ-ent styles of modern deformation, which we de-scribe in this paper.

The Kern Canyon fault has long been consid-ered inactive because a 3.5 Ma lava fl ow (Dal-rymple, 1963) was reported to cap its northern end (Webb, 1936). Our recent fi eld investiga-tions reveal that the basalt is pervasively frac-tured and measurably displaced along the trace

For permission to copy, contact [email protected]© 2010 Geological Society of America

1671

GSA Bulletin; September/October 2010; v. 122; no. 9/10; p. 1671–1685; doi: 10.1130/B30009.1; 9 fi gures; 2 tables.

†E-mail: [email protected]; Current address: Department of Geology and Geophysics, University of Alaska Fairbanks, Fairbanks, Alaska 99775-5780, USA.

Quaternary reactivation of the Kern Canyon fault system, southern Sierra Nevada, California

Elisabeth S. Nadin† and Jason B. SaleebyDivision of Geological and Planetary Sciences, California Institute of Technology, MS 100-23, Pasadena, California 91125, USA

Published online May 20, 2010; doi:10.1130/B30009.1

Nadin and Saleeby

1672 Geological Society of America Bulletin, September/October 2010

of the fault. Our geomorphic and structural stud-ies, presented here, are used to estimate Quater-nary offset along the Kern Canyon fault system. These are distinguished from late Cenozoic ver-tical offsets within the southernmost 200 km of the Sierra Nevada batholith (Fig. 3), which were revealed by low-temperature thermo chrono-metric studies by Mahéo et al. (2009). Persis-tent seismicity associated with the Kern Canyon fault system and the contiguous Breckenridge scarp and White Wolf fault (Ross, 1986), as well as contemporary strain-fi eld models derived in part from seismic studies (Bawden et al., 1997; Unruh and Hauksson, 2009), are also presented and interpreted here to indicate late Quaternary deformation. The high relief of the Kern Can-yon fault scarps (despite high precipitation in the region), as well as a 3.3 ka charcoal layer in ruptured Quaternary alluvium just south of the Isabella basin (U.S. Army Corps of Engi-neers, Lake Isabella Dam Situation Report, January 9, 2009; Hunter et al., 2009), places the Kern Canyon fault activity described in this paper well into the Holocene epoch.

Punctuated fault activity over 100 m.y. and the Neogene and Quaternary remobilizations high-light the importance of the Kern Canyon fault system in the tectonic evolution of the south-western United States. The “Isabella anomaly” is a high-velocity body in the upper mantle

northwest of the Isabella basin (Jones et al., 1994; surface projection outlined in Fig. 2) that has been interpreted to result from the re-moval of ~106 km3 of dense eclogitic material from beneath the southern Sierra Nevada batho-lith (e.g., Ducea and Saleeby, 1998; Jones et al., 2004). The presence of extensional structures in the vicinity of the Isabella anomaly supports pre-dictions that Pliocene removal of dense eclogitic material should increase extensional strain in the area (e.g., Jones et al., 2004). This paper docu-ments fault activity in what was considered a tectonically quiescent region between the active strike-slip San Andreas plate boundary and the actively extending Basin and Range province.

In addition to being geologically signifi cant, the potential continued activity of the Kern Canyon fault is of societal importance: the U.S. Army Corps of Engineers is currently assessing the need to reconstruct a dam that crosses the fault at Engineer Point at the southern end of the Isabella basin (location 3 in Fig. 2). Should the dam fail, it is projected that Bakersfi eld (Figs. 1 and 2), a city of 800,000 people that lies 80 km downstream of Lake Isabella, would be fl ooded within three hours.

In this paper, we present new evidence documenting late Quaternary scarps along the Kern Canyon fault system. These scarps show west-side-up displacements along steeply east-

dipping normal faults that (1) place Cretaceous granitic bedrock of the footwall against Quater-nary alluvium of the hanging wall, and (2) cut and offset a 3.5 Ma lava fl ow. The scarps off-set Pliocene volcanic deposits and Quaternary sedimentary deposits and are classifi ed here as young and potentially active structures of the Kern Canyon fault system. We distinguish them from the ca. 100 Ma damage zone along which they localized, and assess their potential geo-dynamic signifi cance. We also present a synthe-sis of seismic studies to show that normal-fault earthquakes are associated with continued activ-ity along these scarps. Finally, we interpret the reactivation of this fault system in the context of delamination of mantle lithosphere beneath the southernmost Sierra Nevada.

GEOLOGIC SETTING

Several styles and stages of fault-related defor mation overprint one another in the Kern Canyon fault damage zone. A key to under-standing the geologic history of the fault system is to distinguish the structures that are spatially coincident but differ temporally and kinemati-cally. The Kern Canyon fault is a structural zone in which granitic rocks and metasedimentary wall rocks consisting of marble, amphibolite, quartzite, and phyllite are highly fractured,

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Figure 1. Regional tectonic framework, with features dis-cussed in the text. The southern Sierra Nevada batholith and westward adjacent San Joaquin Valley host the main features discussed: the proto–Kern Can-yon, Kern Canyon, Brecken-ridge, and White Wolf faults. Also of note are the Walker Lane–Eastern California Shear Zone belt of seismicity and the Sierra Nevada frontal fault. The box outlines the region shown in Figures 2, 3, 7, and 8.


Geological Society of America Bulletin, September/October 2010 1673

sheared, and altered over a width of ~150 m. For 60 km north of the Isabella basin (Fig. 2, at lati-tude 35.7°N), it is a north-south–striking brittle structure that overprints a mylonite zone termed the proto–Kern Canyon fault (Figs. 1 and 2B; Busby-Spera and Saleeby, 1990).

The proto–Kern Canyon fault is a Late Cre-taceous structure that, along with several other ductile shear zones in the central to southern Sierra Nevada, arose in response to changes in

subduction trajectory of the Farallon plate be-neath the California region (Busby-Spera and Saleeby, 1990; Tikoff and Greene, 1994; Greene and Schweickert, 1995; Tobisch et al., 1995; Tikoff and Saint Blanquat, 1997). The proto–Kern Canyon fault is a dextral reverse-slip fault exposed along an oblique crustal section that traverses ~25 km of batholithic emplacement depths from its northern to its southern end (Pickett and Saleeby, 1993; Nadin and Saleeby,

2008). It is ~150 km long and up to 2 km wide. Foliation within the shear zone dips steeply to the west and to the east. North of the Isa-bella basin to latitude ~36.1°N, ductile fabrics strike northward. South of the basin, they fol-low a slightly sinuous southeastward trajectory (Fig. 2B) and eventually root into lower-crust tectonites of the Rand thrust system, exposed immediately north of the Garlock fault (Nadin and Saleeby, 2008).

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Figure 2. Digital elevation model (DEM, A), fault and lineament map (B), and rose diagram of faults and lineaments (C) of the southern Sierra Nevada. Both the DEM and the fault map show numbered locations of scarps mapped in the fi eld and described in Table 1, as well as the outline of the surface projection of the “Isabella anomaly,” discussed in detail in the text. (A) The DEM is labeled with sparse geo-graphic information so that the reader can examine its topography. (B) The 30 faults and lineaments shown here were mapped in the fi eld and from aerial and advanced spaceborne thermal emission and refl ection radiometer images, and are represented in the rose diagram of (C). USGS—U.S. Geological Survey.

Nadin and Saleeby


The town of Kernville, on the north shore of Lake Isabella, is the dividing point of the proto–Kern Canyon fault and the Kern Canyon fault structural zones. South of latitude 35.7°N, duc-tile and brittle fabrics of the Kern Canyon fault follow a southwesterly route, where they merge with the Breckenridge scarp and, farther south, the White Wolf fault (Figs. 1 and 2B; Ross, 1986). North of the basin, the Kern Canyon fault continues past the proto–Kern Canyon fault to latitude 36.7°N, where it dies out by branching into several faults with displacements of only 0.2–1 km (Moore and du Bray, 1978).

Along the northern segment of the Kern Canyon fault, north of the Isabella basin where it coincides with the proto–Kern Canyon fault (Figs. 1 and 2B), deformation appears to have been progressive. Stages of deformation are seen in an overprinting of the early 2-km-wide mylonite zone fi rst by pervasive brittle fault-ing associated with dextral offset in a fracture zone that is typically ~150 m wide, followed by localized fracture and vertical offset along

discrete, meters-wide breaks. The three stages of deformation are particularly well expressed at Engineer Point, a peninsula at the southern end of the Isabella basin (location 3 in Fig. 2). Early ductile shear is preserved in a zone of S–C mylonites and phyllonites; a later phase of brittle shear led to through-going cataclasis; and late-stage faulting resulted in thin, hematitic gouge zones (Fig. 4; Chester, 2001).

Where the proto–Kern Canyon fault and the Kern Canyon fault diverge south of the Isa-bella basin, brittle overprint along the southern branch of the proto–Kern Canyon fault is rare, and early-phase ductile deformation along the Kern Canyon fault is less pronounced.

Mesozoic Inception

In Late Cretaceous time, the proto–Kern Can-yon fault developed along the axial zone of the southern Sierra Nevada batholith in response to a change in Farallon plate subduction trajectory (Busby-Spera and Saleeby, 1990; Nadin and

Saleeby, 2008). In this region, the 2-km-wide zone of mylonitized batholithic and metasedi-mentary wall rocks forms an intrabatholithic boundary. This boundary is between primarily tonalitic, low-initial 87Sr/86Sr (Sri) plutonic rocks to the west and granodioritic, high-Sri rocks to the east (e.g., Nadin and Saleeby, 2008), and is also detected in seismic studies (Shapiro et al., 2005). Ductile transpressional thrusting with up to 25 km of horizontal shortening across the mylonite zone took place from 100 to 96 Ma and transitioned smoothly into strike-slip shear with ~15 km of dextral offset (Nadin and Saleeby, 2008). Dextral slip continued in the ductile re-gime along the entire length of the proto–Kern Canyon fault until ca. 86 Ma. At this time, exhu-mation of the southernmost end of the batholith brought rocks south of the Isabella basin into the brittle regime progressively with fault motion through time (Nadin and Saleeby, 2008).

The Kern Canyon fault arose in the southwest Sierra Nevada, along the branch south of the Isabella basin, in response to ca. 86 Ma rapid unroofi ng of the batholith. Brittle fabrics of the Kern Canyon fault merged with and overprinted the fabrics of the proto–Kern Canyon fault north of the Isabella basin ca. 6 Ma later, when that region was exhumed into the brittle regime. The predominantly brittle Kern Canyon fault is narrower than the proto–Kern Canyon fault mylonite zone, with ductile-brittle dextral shear localized across a zone of ~150 m width. About 12 km of brittle dextral slip along the Kern Can-yon fault is recorded in offset pluton contacts in the area of the Isabella basin (Ross, 1986; Nadin and Saleeby, 2008).

Oligocene–Miocene Dextral Strike-Slip Reactivation

The Kern Canyon fault system was reacti-vated during Miocene time after a period of early Cenozoic quiescence. Regional evidence suggests there was broad, continuous extension throughout the southern Sierra Nevada and the westward-adjacent San Joaquin basin (Fig. 2) since as early as Oligocene time. Late Oligocene to early Miocene basin subsidence is associated with deep marine deposits, northwest-southeast –oriented normal faults, and syntectonic vol canic fl ows (Bartow, 1991; Goodman and Malin, 1992; Mahéo et al., 2009). In early to middle Miocene time, a distinct phase of growth faulting and associated volcanism took place in the Mari-copa subbasin at the southeast edge of the San Joaquin basin (Fig. 2; MacPherson, 1978; Hirst, 1986; Goodman and Malin, 1992; Mahéo et al., 2009). The southeast Sierra extensional domain, stretching from just north of the Isabella basin to the Tehachapi Mountains (Fig. 2A) also records

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Figure 3. Miocene (ca. 16–10 Ma) reconstruction of the southern Sierra Nevada batholith (SNB). As discussed in the text, northward migration of a slab window gave rise to several north-south extensional features within and east of the central and southern SNB.



early Miocene extension-related volcanism and associated faulting along northwest-striking nor-mal faults (Saleeby et al., 2009; Mahéo et al., 2009). Motion along the Walker basin fault zone was accompanied by the emplacement of closely spaced dikes sourced from the adjacent Cache Peak volcanic center, whose K/Ar and Ar/Ar ages are 16.5–21.4 Ma (Evernden et al., 1964; Bartow and McDougall, 1984; Coles et al., 1997). (U-Th)/He apatite ages as young as 14.8 Ma from the Walker basin refl ect mid-Miocene resetting due to burial, followed by possible rapid exhumation from beneath vol-canic strata (Mahéo et al., 2009).

The Kern Canyon fault is positioned between the Maricopa subbasin and the southeast Sierra extensional domain, and was fi rst reactivated in the brittle regime within a dextral strike-slip transfer zone between these two differentially extending domains. East-side-up vertical motion along the White Wolf segment of the Kern Can-yon fault resulted in the ponding of more than 12 km of Neogene sediments within the Mari-copa subbasin (Goodman and Malin, 1992). A (U-Th)/He apatite study of exhumed Walker basin rocks (Mahéo et al., 2009) indicates west-side-up motion along the Breckenridge segment of the Kern Canyon fault led to ponding of ~2.5 km of sediments in the Walker basin. The zero-offset crossover of scissors-like vertical motions on the oblique-transfer Kern Canyon fault system was the Edison graben (Fig. 2B), at the northwest tip of the modern-day White Wolf fault. The Edison graben is bounded on its southern edge by the Edison fault (Fig. 2B), a southwest-side-up normal fault that initiated in early to middle Miocene time (Dibblee and Warne, 1988) and that merges with the northeast end of the White Wolf fault (Fig. 2B).

Data from another (U-Th)/He apatite study, of basement uplift and river incision, is con-

sistent with Miocene reactivation. Clark et al. (2005) and Clark and Farley (2007) determined that there were two discrete episodes of acceler-ated basement uplift and associated river inci-sion in the southern Sierra Nevada since 20 Ma.

Pliocene Extension and Westward Tilt

We mapped 30 north-south–trending linea-ments in the southern Sierra Nevada from fi eld studies and from examination of aerial imagery. These are (excluding the White Wolf fault) paral-lel to the strike of Mesozoic foliations (Figs. 2B and 2C). Geomorphic and low-temperature thermochronometric data resolve more than 20 west-side-up faults of ~400 m to >2 km in close proximity and parallel to scarps of the Kern Can-yon fault system (Mahéo et al., 2009). These west-side-up normal displacements impart an ~9° westward tilt to the Sierra Nevada basement that continues as a comparable westward-tilted homocline in Tertiary strata of the adjacent east-ern San Joaquin basin. Because of this temporal and structural relation, Mahéo et al. (2009) inter-preted that the offsets occurred on related faults of the Kern Canyon fault system that accommo-dated a late Pliocene (?)–Pleistocene contribu-tion to westward tilting in the southern part of the Sierra Nevada microplate.

West tilt related to the Kern Canyon fault system appears to die out northwards just as the Kern Canyon fault scarps die out northwards. In the southeast San Joaquin basin, the tilted region is bounded by a set of late Paleogene to Quaternary northwest-striking normal faults. These faults controlled the structural evolution of the Edison graben and the Maricopa sub-basin (Fig. 2; Mahéo et al., 2009). The Edison graben lies between the northeast-side-down Edison fault and a set of southwest-side-down normal faults of which the Kern Gorge fault is

the most pronounced (Fig. 2B). The graben is fi lled with ~2.5 km of coarse Oligocene and Miocene fanglomerates and basal ashes of the Cache Peak volcanic center (Goodman and Malin , 1992; Mahéo et al., 2009). On going mapping has revealed that pieces of Edison graben sediment fi ll are broken and displaced on Pliocene–Quaternary faults that are on strike with the Kern Gorge fault. There has been ~700 m of Quaternary displacement on the Kern Gorge fault (Mahéo et al., 2009).

The Kern Gorge and West Breckenridge Mountain faults are the most pronounced of the northwest-striking faults in the southwest Sierra Nevada (Fig. 2B). Between these and the north-south–striking Kern Canyon fault system is the northward-widening, wedge-shaped Breckenridge-Greenhorn horst (Fig. 2), which was uplifted in Pliocene–Quaternary time (Mahéo et al., 2009). Uplift of the Breckenridge-Greenhorn horst and the entire southeast Sierra Nevada resulted in the termina-tion of growth of a >75 km2 submarine fan, the Bena fan (e.g., MacPherson, 1978; Webb, 1981; Dibblee and Warne, 1988), which was depos-ited by the ancestral Bena channel (Fig. 2A). The Bena fan was choked and overlapped with a fl ood of terrestrial sediments that resulted in a delta and fl uvial system.

Further evidence suggesting regional exten-sion in the southern Sierra Nevada batholith is a pulse of Pliocene volcanism centered at ca. 3.5 Ma (Farmer et al., 2002). Pliocene vol-canism in the region is observed to be spatially related to regional extension (e.g., Farmer et al., 2002). The Pliocene volcanic episode in the study area includes deposition of the Little Kern basalt, a lava fl ow at the northern end of the Kern Canyon fault (Fig. 2B; described in detail in the next section) dated at 3.5 Ma by Dalrymple (1963). North-south–oriented,

Figure 4. Photograph (A) and line sketch (B) looking down on Miocene–Holocene brittle features overprinting Creta-ceous mylonitic fabric along the Kern Canyon fault at Engi-neer Point (see Fig. 2A, point 3 for the location, and Fig. 6C for an oblique aerial view of the scarp). Mylonitic fabrics of the proto–Kern Canyon fault, as indicated by stretched, aligned mica grains in granodiorite of (A) and light-gray lines in (B), are transposed from an original north-south strike by brittle deformation and rotation as rigid, broken clasts along the Kern Canyon fault. (B) Brittle overprint is characterized here by through-going cataclasis outlined in light gray, a thinner gouge zone shown in dark gray, and hematite-lined fractures shown as black lines.

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Nadin and Saleeby


ductile-brittle shears in the basalt and a west-side-up scarp within this fl ow (Fig. 5) lie di-rectly along the trace of the Kern Canyon fault.

FIELD EVIDENCE FOR QUATERNARY ACTIVITY

The Kern Canyon fault was fi rst recognized by Lawson (1904), who suggested that the Kern Canyon was a graben between two or more normal faults. More recently, slope breaks and aligned topographic notches along strike of the Kern Canyon fault were identifi ed through a study of aerial photos by Ross (1986), who called some of these notches fault-line scarps. However, despite numerous earthquake epi-centers “in the vicinity” of the fault (Moore and du Bray, 1978), activity had been dismissed by those authors and others since mapping by Webb (1946) defi ned a single trace overlain by un-faulted basalt that was later dated as 3.5 m.y. old (Dalrymple, 1963). Overturning this long-held view, we present here details of prominent geo-morphic features along the Kern Canyon fault that are consistent with late Quaternary, and in some instances Holocene, normal displacement.

Scarps of the Kern Canyon Fault System

The geomorphology of the Isabella basin (Fig. 2A), which was partially fi lled by Lake Isabella after the Kern River was dammed in 1952, is a focal point for investigations of late Quaternary activity of the Kern Canyon fault system. As mentioned earlier, at the Isabella basin the Kern Canyon fault turns from its 025 northeastward strike to a north-south strike that follows the proto–Kern Canyon fault. Ac-tive alluvia tion of the Isabella basin is burying mountainous topography east of the Kern Can-yon fault, but west of the fault, the Kern River and Walker Creek canyons are deeply incised

into granitic and metamorphic basement rocks in a manner typical of southwestern Sierra Nevada gorges that were incised since 2.7 Ma (Stock et al., 2004). This suggests relatively ac-celerated uplift of the mountainous terrain west of the Isabella basin.

Meter-scale prominent scarps and Quater-nary alluvium-fi lled basins run the length of the Kern Canyon fault. These and related promi-nent linear topographic breaks (lineaments) of the southern Sierra Nevada batholith (Fig. 2B) were mapped from fi eld studies, aerial photog-raphy, and digital elevation model (DEM) and advanced spaceborne thermal emission and refl ection radiome ter (ASTER) images. Their locations are differentiated with color in Fig-ure 2B by the method used to identify them, and they are listed and described in Table 1. The locations of documented Quaternary fea-tures listed in Table 1, and selected aerial photo-

graphs taken during a helicopter survey of the Kern Canyon fault (Fig. 6), are also keyed to Figure 2. Some prominent geomorphic features indicative of recent Kern Canyon fault activity are briefl y described here, starting in the north and proceeding south. Most of these features are also easily discernable in Google Earth images.

At 36.6°N, the Kern Canyon fault terminates in a 1-km-wide, U-shaped trough. Proceeding southward, the west side of the Kern Canyon is bounded by a 400-m-high cliff that is con-tinuous (except where it is carved by east-west–running stream channels) for ~26 km along strike of the Kern Canyon fault. Discontinu-ous scarps at the base of the cliff are typically ≥20 m high and trap patches of alluvium east of the fault. Moore and du Bray (1978) noted the presence of a hot spring and a mineral spring near latitude 36.5°N, both close to the fault, but neither of these has been described in the

2 m N

N

A

B

Kern Canyon fault

Kern Canyon fault

20 m

Figure 5. Photographs of the Kern Canyon fault in the Little Kern lava fl ow (Fig. 2 location 7, and mapped in yellow on Fig. 2B), from the air (A) and from the ground (B). (A) A 20-m topographic notch appears west of the Kern Canyon fault. Note also the pervasive shearing of basalt in the left foreground. (B) On the ground, blocky basalt outcrops of the intact foot-wall end suddenly along the trace of the fault, leaving an ~2-m-high scarp, and basalt east of the fault is sheared and eroded from the fault to ~50 m east of the hanging wall.

TABLE 1. SUMMARY OF SCARPS MAPPED AND KEYED TO LOCATIONS SHOWN IN FIGURE 2

Keyed locationnoitpircseD)2.giFees(

Length of feature

Estimated Quaternary normal offset

1—Walker basin Breckenridge scarp forms west side of basin; K granitic basement to west traps sediment in basin. 700 m to Miocene strata.

8 km ~1300 m since Late Miocene (Mahéo et al., 2010)

2—Havilah Valley Linear normal fault scarp bounds western side of Qal-fi lled valley. Streams bisect scarp here. 1 km ~10 m based on scarp height3—Engineer Point and

Isabella basinEngineer scarp is a normal fault scarp. Basin fi ll is Qal, up to 30 m thick at Engineer Point and

trapped against K granitic basement to west. Some Qal overlaps Kern Canyon fault (KCF).9 km 30 m based on depth of Qal fi ll

4—Cannell Creek pracsnodesabm7muminiMmk2.sedishtobnoepytkcoremas;pracstnenimorPheight

5—Brush Creek pracsnodesabm7muminiMmk51.sedishtobnoepytkcoremas;pracstnenimorPheight

6—Rincon Spring K basement in fault contact with Q debris fl ow. Abandoned stream channels in footwall block. 0.3 km Minimum 4 m based on scarp height

7—Little Kern basalt fl ow

Tertiary basalt deposit, sheared and fractured along trace of KCF. Sharp topographic notch along KCF trace.

~0.5 km Minimum 20 m based on height of topographic notch.

8—Trout Meadows to Willow Meadows

N–S elongate linear valleys, with Qal valley fi ?mk2>.FCKfotsaedeppartll

9—Little Kern lake and rockfall

Lake formed by damming of Kern River during earthquake-triggered rockfall of 1868. N/A N/A



geological literature. The Kern Canyon widens at Little Kern Lake, which formed in 1868 on the west bank of the Kern River when ~0.2 km3 of rock dammed the river during earthquake-triggered failure (Townley and Allen, 1939; Ross, 1986) of the canyon’s eastern slope. South of the lake, more elongate, fl at, alluvium-fi lled meadows line the Kern Canyon fault in the midst of rugged topography.

At latitude ~36.2°N, the Kern Canyon fault leaves the Kern River channel and cuts through a steep, ~450-m-high cliff capped by a 3.5 Ma basalt (Fig. 5A; Webb, 1936, 1946; Dalrymple, 1963; Moore and du Bray, 1978) that is on aver age ~100 m thick but locally thickens in paleochannels to ~300 m (Dalrymple, 1963). The basalt cap is the most commonly cited evidence for lengthy quiescence of the Kern Canyon fault. Probably because it is only acces-

sible via lengthy, rugged trails or by helicopter, fi eld observations come only from the original reports by Webb (1936, 1946). In these reports, Webb simply stated that a series of lava fl ows covered the trace of the fault, and that there was no evidence with which to ascertain the nature of movement on the Kern Canyon fault. [Moore and du Bray (1978) subsequently veri-fi ed Hill’s (1955) mapping of the Kern Canyon fault as dextral and estimated offset at 7–13 km, increasing from north to south.] Despite numer-ous earthquake epicenters in the vicinity of the fault (described in detail in the next section), Moore and du Bray (1978) concluded that there was no measurable offset of the basalt since its deposition. However, they were looking for dextral offset consistent with their observations of offset pluton contacts. Post–3.5 Ma activity along the Kern Canyon fault was thus dismissed

(e.g., Jones and Dollar, 1986; Busby-Spera and Saleeby, 1990), despite the seismic activity in the area.

We report here evidence gathered from fi eld investigations facilitated by the U.S. Army Corps of Engineers that the Kern Canyon fault displaces the basalt cap. As seen from the air, the lava surface is broken by a sharp topo-graphic notch of ~20 m height on the west side of the Kern Canyon fault trace (Fig. 5A). On the ground in this location, generally coherent out-crops west of the fault end abruptly in a gully where deeply weathered basalt is pervasively sheared and fractured parallel to the trace of the Kern Canyon fault, resulting in an apparent west-side-up scarp of ~2 m height (Fig. 5B). Because the topographic break along the trace of the fault is deeply weathered, the fault here is expressed as a zone of pervasive fracture ~50 m

Figure 6. Photographs of some key scarps discussed in the text, with the Kern Canyon fault sketched in as a dashed line for reference. (A) Oblique aerial photograph of an eroded scarp at Rincon Spring (location 6 on Fig. 2) is ~4 m high. Stream channels are deeply incised into the uplifted footwall but do not cross the ponded Quaternary alluvium of the hanging wall. Letter B indicates the loca-tion of (B) Cretaceous granitic basement in fault contact with Quaternary glacial debris. The fractures in the granitic basement strike northward, parallel to the strike of the Kern Canyon fault, shown as a white line. (C) Oblique aerial photograph of Engineer Point (location 3 on Fig. 2), a focus of U.S. Army Corps of Engi-neers (USACE) investigations because it is the site of a dam that crosses the Kern Canyon fault. It is also the fault contact between Cretaceous basement and Quaternary alluvium at the western edge of the Isabella basin, and this fault contact is continuous for 9 km south-wards through the town of Lake Isabella and into Havilah Valley. (D) A short scarp (10 m high) forms a basement-alluvium fault contact at the west edge of Havilah Valley (location 2 on Fig. 2). USACE trenching through the hang-ing wall alluvium in Havilah Valley reveals sediment deformed by liquefaction, and another trench just south of Havilah Valley yielded a 3.3 ka charcoal age in ruptured alluvium (USACE Lake Isabella Dam Situation Report, January 9, 2009; Hunter et al., 2009).

B

N

A

B

C

N

D

N

west

Stre

am c

han

nel

sin

cise

d in

to fo

otw

all

Nadin and Saleeby


wide rather than as a single, discrete fault plane with confi dently measurable vertical displace-ment. In normally faulted bedrock, slip often takes place both along normal faults and on fractures around the fault, leading to degraded or irregular scarps at the surface whose ages and slip amounts can be misinterpreted (Hilley et al., 2001). Petrographic analysis of basalt from both sides of the Kern Canyon fault shows that the capping fl ow is compositionally uniform, thus supporting the presence of a true fault scarp.

For much of its length from the lava fl ow to 36°N, the main Kern Canyon fault trace forms a sharp linear feature on aerial images. At this lati-tude, we document (1) a subdued, ~4-m-high, north-south–striking scarp on whose footwall east-west–oriented stream channels are cut off (Fig. 6A) and (2) Late Cretaceous granitic base-ment rocks in fault contact with a Quaternary debris fl ow deposit (Fig. 6B) whose clasts are sheared and fragmented. Nadin and Saleeby fi rst reported this fault contact (2001) and re-corded pervasive fractures in the basement rock that strike 005°/185° and dip 80°–85° eastward, concordant with the strike of the scarp. Pro-ceeding south, west-side-up scarps are several meters in height and show disruption of the same rock type on both sides of the fault or they juxtapose similar rock types (e.g., granodiorite and mica-rich quartzite). The scarps are discon-tinuous here, in that they are covered in places by alluvial fi ll whose upper surface is probably less than 5000 yr old (Page, 2005).

Engineer Point is a basement-rock scarp that projects into Isabella basin and is ductilely to brittlely sheared across its ~100-m width (Figs. 4 and 6C). It has been well studied in the context of earthquake safety because an earthen dam that traps Kern River water for fl ood con-trol and irrigation was constructed across this peninsula in 1952. As part of their efforts to assess the vulnerability of the Engineer Point dam, the U.S. Army Corps of Engineers under-took coring, trenching, and a seismic refraction study that was reported by Page (2005). High P-wave velocities in Quaternary alluvium east of the Kern Canyon fault indicate ~30 m of sediment is trapped against uplifted Cretaceous granitic basement to the west, suggesting at least this much vertical displacement along the fault at this latitude. The Engineer Point scarp continues for ~9 km south of the Isabella basin but is obscured by development in the town of Lake Isabella. Just south of Lake Isabella, a U.S. Army Corps of Engineers trench through ruptured alluvium yielded a 3.3 ka charcoal age (U.S. Army Corps of Engineers, Lake Isabella Dam Situation Report, January 9, 2009; Hunter et al., 2009). About 2 km south of this trench site, the presence of hot springs also indicates

active faulting. Another scarp emerges on the west side of the Havilah Valley (Fig. 6D). This scarp is an ~10-m-high linear ridge of shattered basement that forms the western boundary of a fl at alluvium-fi lled valley. Another trench through the hanging wall alluvium here reveals an isotropic sediment mass with fl oating bed remnants, suggesting deformation by liquefac-tion. Scarps of the Kern Canyon fault system continue as the Breckenridge fault at latitude 35.4°N (Fig. 2B). Apatite He data and geomor-phic evidence indicate ~2.1 km of west-side-up displacement on the Breckenridge segment since Miocene time (Mahéo et al., 2009).

Several lines of fi eld evidence indicate that the Quaternary scarps resulted from west-side-up, normal offset on the Kern Canyon fault. First, all of the north-south–elongate depressions fi lled with Quaternary alluvium along the Kern Canyon fault trace are bounded on their west-ern sides by basement rocks, suggesting that basement forms the footwall of a normal fault. Second, although eroded scarps are commonly crossed by stream channels (as in the Havilah Valley, Fig. 6D), in several locations east-west–running stream channels of the Kern Canyon fault footwall end abruptly at a scarp (Fig. 6A). Because lateral stream offsets are absent, this suggests that the channels are steeply incising into the rapidly uplifted western footwall of the system. Sediment that ponds above the hanging wall originates from the generally more rugged

terrain east of the fault, and is trapped against the footwall. Finally, the 3.5 Ma lava fl ow is perva-sively sheared and fractured exclusively along the trace of the Kern Canyon fault, and the shear-ing coincides with an ~20-m-high, west-side-up, topographic break through compositionally uni-form material (Fig. 5). West-side-up faulting was therefore contemporaneous with or postdated the lava fl ow. Pervasive tensile and shear fracturing is consistent with deformation of weak material in the hanging wall of a normal fault. Further evidence supporting normal offsets of the Kern Canyon fault system in Quaternary time comes from geodetic and seismic studies.

RECENT GEODETIC AND SEISMIC ACTIVITY

Analysis of seismicity within and along the southern Sierra Nevada batholith shows that earthquakes along the Kern Canyon fault sys-tem occur on shallow normal faults (Fig. 7). In the Sierra Nevada east of the Kern Canyon fault, earthquakes occur on a combination of dextral strike-slip and normal faults, and to the southeast and southwest, they occur on sinistral strike-slip and thrust faults. Strain-meter and global positioning system (GPS) measurements further indicate that the Kern Canyon fault sys-tem is undergoing horizontal extension and that the southern Sierra Nevada is uplifting relative to adjacent basins.

35° N

35.5°

36° N

36.5°

Depth (km)0

5

10

15

20

WW

F

BF

KC

F

DM

WP

118.5°119° W 118° W119.5°

Figure 7. Seismicity map of the study area, showing all earth-quakes of M >3 since 1981, colored according to depth. Focal mechanisms are for well-constrained M >4.0 events since 1999. The regions of the Durrwood Meadows (DM) and Walker Pass (WP) earthquake swarms are outlined. Relo-cated focal mechanisms and earthquake locations are from Clinton et al. (2006), Tan (2006), and Lin et al. (2007). KCF = Kern Canyon fault, BF = Breck-en ridge fault, and WWF = White Wolf fault.



Seismicity

In the past 35 years, there have been more than 200 earthquakes greater than M = 3 and at depths less than 10 km in the vicinity of the Kern Canyon fault—between latitudes 35°N and 37°N and longitudes 118.3°W and 118.85°W. The focal mechanisms for these earthquakes yield further insight into the nature of active faulting in the southern Sierra Nevada (Fig. 7). The Durrwood Meadows earthquake swarm, which lasted from October 1983 to May 1984 (Fig. 7), is the most pronounced re-cent seismic activity in the vicinity of the Kern Canyon fault. This swarm comprised >2000 measured earthquakes, many of which were M ≥3.0 and the largest of which was M = 4.9 (Jones and Dollar, 1986). It was localized ~10 km east of the Kern Canyon fault and occu-pied a discrete, ~100-km-long, north-south ver-tical plane (Lin et al., 2007) with no evidence of ground breakage. All calculated earthquake depths were 0–7 km, all but one M >3.0 oc-curred between 4.0 and 5.9 km, and all resolved focal mechanisms were consistent with pure west-side-up, dip-slip displacement (Jones and Dollar, 1986; Clinton et al., 2006). These obser-vations, coupled with the lack of coincidence of the Kern Canyon fault with the swarm, exclude the possibility that the earthquakes occurred on the main Kern Canyon fault trace. It suggests, however, creep is taking place on a nascent fault that may be part of the Kern Canyon fault system, or is at least the easternmost expres-sion of southern Sierra Nevada normal faulting that began in late Cenozoic time. We empha-size here that the Quaternary scarps of the Kern Canyon fault comprise the easternmost surface breaks in a kilometers-wide zone comprising several late Cenozoic, near-vertical, parallel fault strands.

Seismic activity of note that probably took place on the Kern Canyon fault proper includes a two-week-long series of earthquakes with more than 500 aftershocks that occurred near Kernville in 1868 (Treasher, 1949; Ross, 1986) and triggered the rockfall that led to the creation of the Little Kern Lake. The largest of these was later assigned M = 6.5 (Barosh, 1969). More recently, several M ≥3.0 earthquakes have oc-curred along the Kern Canyon fault. Two exam-ples, from July 1999 and April 2001, are very well constrained, less than 10 km deep, M = 4.2 and M = 4.1 earthquakes, respectively (Fig. 7; Tan, 2006). The 1999 event occurred ~1.8 km west of the Kern Canyon fault at the latitude of the Isabella basin, and the 2001 event occurred ~10 km east of the Kern Canyon fault at latitude ~36°N. The focal mechanisms for both indicate normal offset along north-striking planes.

While focal mechanisms near the north-south–trending segment of the Kern Canyon fault show exclusively normal slip on north-striking faults, with the majority of seismic ac-tivity occurring less than 10 km deep, seismicity to the east and to the southwest is markedly dif-ferent. In the eastern Sierra range front, earth-quake focal planes show predominantly dextral slip on north-northwest–striking faults, and most of the focal depths are 5–15 km (Fig. 7). This is in good agreement with measure ments of offset and calculations of slip rate from the Sierra Nevada frontal fault zone, which show dominantly dextral slip with subordinate nor-mal slip (e.g., Le et al., 2007). In the south-west Sierra, seismicity in the region of the Breckenridge-Greenhorn horst is consistent with active uplift of the horst (Mahéo et al., 2009). As shown in Figure 7, focal mechanisms in the area where the White Wolf fault meets the southern tip of the Breckenridge fault show sinistral slip along northeast-striking fault planes parallel to the trace of the White Wolf fault, and focal depths are mainly 5–10 km. Where the White Wolf fault reaches into the southern San Joaquin basin, abundant focal mechanisms all show northward thrusting along east-west–striking fault planes, again parallel to the trace of the White Wolf fault, and much deeper focal mechanisms of up to 20 km. The 1946 Walker Pass earthquake swarm (Fig. 7) presents yet an-other type of seismic activity, of sinistral strike-slip shear along northeast-striking planes (e.g., Bawden et al., 1999).

Strain

Short-term strain studies across the Kern Canyon fault led Vali et al. (1968) to suggest that ground motions recorded by strain meter as “spikes in strain” could be caused by “small slippage” along the fault. Slade et al. (1970) con-ducted further analyses of the relative motion between the two arms of the strain meter, which were oriented parallel and perpendicular to the fault. They found that over one two-day interval, bedrock on the western wall of the fault moved ~0.5 mm in a vertical direction, and suggested: “the motion observed at this site arises from forces perpendicular to the fault as a whole.” This implies east-west extension that could re-sult in west-side-up motion on the Kern Canyon fault. While the Slade et al. (1970) study was inconclusive with regard to permanent offset, it did show that strain across the fault is 25 times that of the adjacent bedrock.

Regional geodetic and seismologic analyses indicate overall northwest-southeast extension (Bennett et al., 2003) and horizontal plane strain (Unruh and Hauksson, 2009) across the Sierra

Nevada microplate. This regional strain fi eld is punctuated locally by (1) horizontal extension with vertical crustal thinning within the south-ern Sierra Nevada (Unruh and Hauksson, 2009), and (2) shortening across the southwest tip of the Sierra Nevada, where measurements from a geodetic array spaced between Bakersfi eld and the Garlock fault (Figs. 1 and 2) indicate a maximum principal strain azimuth oriented 300° and strain rates of ~0.2 μstrain/yr that in-creased 300% just before the 1952 Kern County earthquake (Bawden et al., 1997). P- and T-axes computed by Bawden et al. (1999) are consis-tent with two distinct styles of strain: east-west–oriented sinistral strike-slip motion between the Walker Pass and the region of the White Wolf fault–Breckenridge transition (Fig. 7), and a northward-trending zone of east-west extension aligned with and close to the trace of the Kern Canyon fault.

Global Positioning System Velocities

To assess the contemporary horizontal and vertical velocities of the southern Sierra Nevada batholith, we concentrate here on GPS data, publicly available on the Southern California Integrated GPS Network (SCIGN) Data Portal (http://reason.scign.org), from 32 stations in and around the southern half of the batholith (Fig. 8 and Table 2). Many of these stations have been installed only in the past few years, but they still provide valuable insight into relative motion in this part of the range.

Horizontal velocities, shown by the vectors on Figure 8, are considered relative to station LNCO (Lind Cove) because it has been actively recording data the longest (since 1999). Relative to LNCO and at latitudes where the Kern Can-yon fault is a north-south–striking lineament, 10 of 11 stations west of the fault are moving westward at rates between 0.6 and 6.8 mm/yr (Table 2). In contrast, stations east of the Kern Canyon fault at these latitudes show predomi-nantly eastward motion relative to LNCO. The southwesternmost part of the batholith shows a more complicated pattern, probably caused by Garlock fault sinistral motion, sinistral slip along the White Wolf fault, and northward thrusting along the San Emigdio–Tehachapi fold-thrust belt (Figs. 2A and 8; Nilsen et al., 1973; Good-man and Malin, 1992; Mahéo et al., 2009).

Vertical velocity values with error estimates for stations in the southern Sierra Nevada re-gion are shown in Figure 8 and listed in Table 2. These velocities are inherently less precise than the horizontal components for several reasons, including hydrologic and atmospheric infl u-ences (Blewitt et al., 2001). However, general information can be gained from the regional

Nadin and Saleeby


pattern , and the vertical motions of six stations in this area are described by Fay et al. (2008). We chose the combination velocity solu-tion from the National Aeronautics and Space Admini stration’s Research, Education, and Appli cations Solutions Network (REASoN; Fig. 8 and Table 2) primarily because these val-ues agree better with the precise values of the six stations analyzed by Fay et al. (2008). The pat-tern that emerges is one of uplift of all stations within the Sierra Nevada batholith at rates of 0.4 to 2.4 mm/yr. In contrast, all stations in the Owens Valley to the east are moving downwards at rates of up to 3.6 mm/yr, and those in the San Joaquin basin to the west are moving down-wards at much higher rates of 0.7 to 22.2 mm/yr (probably refl ect ing widespread groundwater

removal; e.g., Lofgren and Klausing, 1969). The precise determinations of relative vertical mo-tions for six of the stations shown in Figure 8 (highlighted in bold print) indicate the same overall pattern, with the southern Sierra Nevada stations moving up at rates of 0.42 to 0.53 mm/yr and the Owens Valley stations moving down at rates of ~0.66 to 0.79 mm/yr relative to station ARGU in the Argus Range of eastern Califor-nia (Fig. 8; Fay et al., 2008). Because these and further detailed studies of vertical velocities in the region are consistent with the REASoN values (R. Bennett, 2008, personal commun.), we feel confi dent that the pattern is real and, furthermore, that vertical velocities west of the Kern Canyon fault are generally higher than those east of the fault.

DISCUSSION

The Kern Canyon fault zone is the only ac-tive structural zone that breaks the interior of the Sierra Nevada batholith, disrupting the struc-tural coherency of the batholith. Its longevity and geometry make it well positioned to ac-commodate the present regional east-west ex-tensional stress fi eld. Structural, geomorphic, geodetic, and seismic observations presented here indicate that the Kern Canyon fault sys-tem has undergone Quaternary reactivation as a series of west-side-up normal fault scarps along its 130-km length. This remobilization is consis-tent with structural and stratigraphic data from the adjacent southeastern San Joaquin basin and from low-temperature, thermochronometric

5 mm

N

0.7(0.2)–10.2

(0.5)

–22.2(0.8)

2.4(0.6)

–12.3(1.1)

0.45(0.09)

2.3(0.4)

0.53(0.09)

–15.0(0.4)

2.2(0.4)

0.42(0.09)

–3.6(0.2)

0.0(0.09)

–0.66(0.12)

–0.79(0.12)

0.5(0.3)

0.2(0.5)

1.8(0.2)

–2.0(0.2)

–4.5(0.7)

–0.7(0.2)

Kern

Can

yon

faul

t

White W

olf fault

Garlock fault

San Andreas fault

SanJoaquin

Valley

Ow

ens Valley

1.7(0.2)

LNCOP566

P056

P571

P565

ISLK

P567

P558THCPARM2

P557

P559

BEPK

P570

COSO

ARGU

P569P616

CCCC

RAMT

P568

P591

P579

P562

P560

EDPP

WGPP

P467P572

P564

P563

BVPP

Wheeler Ridge thrust

118.5°119° W 118° W

35° N

36° N

36.5°

35.5°

Figure 8. Global positioning system stations of the south-ern Sierra Nevada, westward adjacent San Joaquin Valley, and eastward adjacent Owens Valley. Lines indicate hori-zontal motion with respect to station LNCO (in bold print, in the northwest corner of the map), which has been collecting data the longest (since 1999). Numbers indicate vertical ve-locities (excluding stations col-lecting only since 2006), with italicized numbers highlighting upward motion. All numbers are Combine fi ltered velocities from the National Aeronautics and Space Administration’s Research, Education and Ap-plications Solutions Network (REASoN) website (see Table 2 for velocities and Global Posi-tioning System Velocities sec-tion for explanation of REASoN Combine fi lter), except for the numbers shown in bold, which are high-confi dence determina-tions from Fay et al. (2008) that are calculated with respect to station ARGU, the easternmost station on this fi gure.



determinations (Mahéo et al., 2009) that link the Kern Canyon fault system with active uplift of the Breckenridge-Greenhorn horst (as also sug-gested by vertical displacement of GPS station P567, Fig. 8). The southwest edge of the horst is defi ned by northwest-striking, principally southwest-side-down, normal faults, some with reported Quaternary scarps (Fig. 2B; Mahéo et al., 2009).

After early Cenozoic quiescence, the Kern Canyon fault system was fi rst reactivated in early Miocene time, corresponding to a period of regional uplift. (U-Th)/He apatite ages and geomorphic analyses indicate two discrete epi-sodes of accelerated river incision in the south-ern Sierra Nevada since 20 Ma (Clark et al., 2005; Clark and Farley, 2007). We suggest that the fi rst is related to ca. 10 Ma regional exten-sion. Mahéo et al. (2009) and Saleeby et al. (2009) document early to middle Miocene ex-tension in the southern Sierra Nevada and the southeast San Joaquin basin that suggests struc-tural continuity of the White Wolf fault with the Kern Canyon fault at that time. The integrated system partitioned differential extension across northwest-striking normal faults in the Mari-copa subbasin (Fig. 2) from northwest-striking

normal faults of the southeast Sierra extensional domain. Westward tilt and uplift of the horst re-moved from the basement the Tertiary strata that had been continuous with westward-dipping Tertiary sediments in the adjacent eastern San Joaquin basin.

Evidence throughout the eastern margin of the Sierra Nevada microplate indicates that, by middle Miocene time, it lay in a generally extensional tectonic setting (Fig. 3), moving ~15 mm/yr to the northwest relative to North America (Wernicke and Snow, 1998). Such ex-tension, as expressed by normal faulting along the current eastern edge of the Sierra Nevada, likely marks the inception of the Sierra Nevada micro-plate (Argus and Gordon, 1991). The Ricardo Group, a 1700-m-thick sequence of Miocene vol-canic and lacustrine sediments deposited between ca. 19 and 7 Ma in the El Paso basin southeast of the Sierra Nevada batholith (Fig. 3), docu-ments a change from north-south extension at 17–15 Ma (attributed to northward migration of a slab window beneath western North America; see also Cox and Diggles, 1986; Monastero et al., 1997) to east-west extension north of the Garlock fault in the El Paso basin at 10–9 Ma (Loomis and Burbank, 1988). The transition to

east-west extension ca. 10 Ma is also recorded in the central Sierra Nevada by volcaniclastic rocks of the Carson Pass, ~10 km south of Lake Tahoe (Fig. 1). Volcanic sequences that were ex-truded 14 m.y. ago were deposited in Cretaceous paleochannels and reincised 4 Ma later and cut off from sources to the east; this late Miocene reincision was ascribed to uplift attendant with passage of the triple junction through the lati-tude of the central Sierra Nevada (Busby et al., 2008). The emergence of the southeastern Sierra Nevada as a sediment source and topographic upland by 8 Ma is also recorded in Ricardo Group sediments (Loomis and Burbank, 1988). This is consistent with the Miocene uplift and normal faulting reported by Mahéo et al. (2009). It also coincides temporally with the 10–9 Ma Stanislaus Group of voluminous volcanic de-posits in the central Sierra Nevada, which was proposed to have erupted at a releasing stepover on dextral transtensional faults that created the largest Miocene volcanic center in the Sierra Nevada (Putirka and Busby, 2007).

The second episode of post–20 Ma acceler-ated river incision in the southern Sierra Nevada noted by Clark et al. (2005) and Clark and Farley (2007) initiated ca. 3.5 Ma. This timing

TABLE 2. VERTICAL VELOCITIES OF GLOBAL POSITIONING SYSTEM STATIONS AS REPORTED ON THE REASoN WEBSITE

Name Latitude Longitude Data since Combine fi ltered Error JPL fi ltered Error SOPAC fi ltered Error PBO offi cial ErrorLNCO (LIND) 36.3603 –119.0576 1999 0.7 0.2 1.3 0.2 0.4 0.2 N/AP566 36.324454 –119.229286 2005 –10.2 0.5 –8.8 0.1 –10.7 0.4 –10.1 0.2P056 36.027437 –119.062869 2005 –22.2 0.8 –21.5 0.1 –23.4 0.7 –22.2 0.3P571 36.231366 –118.766715 2005 2.4 0.6 4.3 0.1 2.4 0.5 4.7 0.2P565 35.743893 –119.236652 2005 –12.3 1.1 –15.5 0.1 –14.9 1 –16.1 0.1ISLK 35.662271 –118.4743 1999 0.7 0.2 1.7 0.2 0.3 0.2 1.3 3.5P567 35.420946 –118.753576 2005 2.3 0.4 3.4 0 1.8 0.4 2.1 2.7P558 35.138605 –118.611654 2006 2.6 0.5 5.2 0.1 2.1 0.4 3.5 0.2THCP 35.158182 –118.414571 2000 0.8 0.1 2 0.1 0.1 0.1 –1.2 –3.8ARM2 35.20119 –118.90962 2000 –15 0.4 –14 0.3 –12.9 0.4 5.1 1.2P557 34.944385 –118.655586 2005 2.2 0.4 3.2 0.1 2 0.4 3.7 0.5P559 34.838909 –118.617597 2005 1.7 0.2 2.8 0.1 2 0.1 2.5 0.2P465 36.466829 –118.132419 2007 –45 3.6 10.4 0.5 4.7 0.7 13.2 2.5P573 36.0930943 –118.260498 2008BEPK 35.878388 –118.074092 2000 0.7 0.2 1.8 0.2 0.2 0.2 –1 3.9P570 35.667348 –118.260038 2006 –0.4 1.4 1.5 0.1 –1.4 1.3 2.5 1COSO 35.98231 –117.80797 2000 –3.6 0.2 –3 0.2 –4 0.2 7.9 0.9ARGU 36.05 –117.521944 2000 –0.9 0.3 0.4 0.3 –1.2 0.3 N/AP569 35.377964 –118.123752 2007 0.7 1.2 3.5 0.2 2.8 1 7.5 0.5P616 35.42454 –117.89328 2007 –3.4 0.5 2.3 0.2 0 0.4 7.6 0.6CCCC 35.56531 –117.67117 2000 –0.3 0.2 1 0.1 –1 0.2 –3.1 3.7RAMT 35.338714 –117.683349 2000 –0.6 0.2 0.5 0.1 –1 0.2 –1.5 3.6P568 35.254302 –118.126498 2007 2.6 1.1 4.4 0.2 4 0.9 9.6 0.4P591 35.152424 –118.016474 2005 0.5 0.3 1.8 0.1 0.1 0.3 0.8 0.3P579 35.038762 –118.005764 2006 1.2 0.2 2.3 0.1 0.5 0.1 1.6 0.2P562 34.982133 –118.188744 2004 –0.1 0.3 1.4 0.1 –0.4 0.3 –0.4 3.7P560 34.82181 –118.540866 2005 0.2 0.5 2.3 0.1 –0.9 0.5 –2.5 4.7EDPP 34.946194 –118.830408 2000 1.8 0.2 3.3 0.1 1 0.2 –1.4 4.2WGPP 35.010848 –118.983687 2000 –2 0.2 –0.9 0.1 –2.4 0.2 –4 3.7P467 36.570202 –118.090623 2006 5.7 1 4.2 0.1 –0.2 0.9 4 0.2P572 36.585511 –118.954581 2006 3.7 0.7 5.1 0.1 3.5 0.5 3.2 1.3P564 35.62291 –119.34938 2006 –59.7 2 –56.1 0.1 –58.9 0.7 –53.9 0.3P563 35.418669 –119.421165 2005 –4.5 0.7 –4.7 0.1 –5.4 0.6 –4.8 0.2BVPP 35.157276 –119.347506 2000 –0.7 0.2 0.8 0.2 –1.2 0.2 –3 4.9

Note: Combine fi ltered data are shown in Figure 8, with the exception of stations ARGU, CCC, RAMT, THCP, BEPK, and ISLK. Stations in bold have only been collecting data since 2006 and were discounted from Figure 8. REASoN—Research, Education, and Applications Solutions Network (National Aeronautics and Space Administration [NASA]); JPL—Jet Propulsion Laboratory (NASA); SOPAC—Scripps Orbit and Permanent Array Center (Scripps Institute of Oceanography); PBO—Plate Boundary Observatory (National Science Foundation Earthscope Program).

Nadin and Saleeby


is supported by pre–2.7 Ma amplifi ed bedrock uplift that drove accelerated river incision for west-draining rivers located between latitudes 36.5°N and 38°N (Stock et al., 2004). It is also in good agreement with a central Sierra Nevada study suggesting that topography in the range resulted from two periods of uplift, including stream incision of up to 1 km since ca. 5 Ma (Wakabayashi and Sawyer, 2001).

The disrupted Little Kern lava fl ow and Qua-ternary scarps described here (Fig. 2 and Table 1) are consistent with the most recent phase of Kern Canyon normal faulting beginning ca. 3.5 Ma. Given the spacing between scarps along the Kern Canyon fault, it is likely that the fault has ruptured discontinuously along its length since that time. The lowest slip-rate limit for the Kern Canyon fault comes from the scarp in the basalt fl ow at the fault’s north end: if 20 m of offset oc-curred over the past 3.5 Ma, this yields a slip rate of 0.006 mm/yr. Until more accurate determina-tions of the total slip and the timing over which it took place can be made for the northern part of the Kern Canyon fault, this slip rate should be considered a lower limit. The basalt in this loca-tion is pervasively fractured over a 50-m-wide zone, and it is likely that the fractures near the main fault trace also accommodated offset, as suggested by Hilley’s et al. (2001) study of dis-tributed offset in fracture zones around normal faults. Furthermore, fi eld mapping and apatite He thermochronologic data indicate that addi-tional west-side-up normal scarps lie west of the Kern Canyon fault trace and the lava fl ow cap (Mahéo et al., 2009). Indeed, there are often par-allel scarps along the Kern Canyon fault system (Fig. 9). Slip rates on all these faults must be in-cluded in the rate along the Kern Canyon fault in order to more thoroughly assess the Quaternary kinematics of the system.

In the Isabella basin, a 30-m-high scarp of Cretaceous granitic basement traps Quaternary alluvium east of the fault. If 30 m of slip in this location also occurred over the past 3.5 Ma, which is an early date for inception of pure nor-mal faulting as documented by the sheared lava fl ow, this suggests a slip rate of ~0.01 mm/yr. Differential vertical motions of well-constrained GPS stations ISLK and BEPK (Fay et al., 2008), which are on either side of the Kern Canyon fault (Fig. 8), suggest a comparable slip rate of 0.03 mm/yr. However, this is an order of magni-tude lower than Holocene vertical slip rates es-timated for the Sierra Nevada frontal fault (e.g., Le et al., 2007), and up to two orders of mag-nitude less than the uplift of the Sierra Nevada batholith relative to Owens Valley as estimated by Fay et al. (2008).

It is likely that the most recent phase of nor-mal fault activity along the southern part of the

Kern Canyon fault began in mid-Quaternary time, as suggested by the contiguously tilted relict landscape surface and early to mid-Quaternary lacustrine deposits (Saleeby et al., 2009; Mahéo et al., 2009). Mid-Quaternary in-ception suggests a slip rate of 3.0 mm/yr at the Isabella basin, which is higher than our previ-ously mentioned estimate. The 3.3 ka charcoal layer in ruptured Quaternary alluvium just south of the Isabella basin (U.S. Army Corps of Engineers, Lake Isabella Dam Situation Report, January 9, 2009; Hunter et al., 2009) places Kern Canyon fault activity at this lati-tude well into the Holocene epoch.

While placing slip-rate bounds of 0.01 to 3.0 mm/yr on the scarp at Isabella basin is a useful guide, we reiterate that the abundant and often parallel scarps along the Kern Canyon fault (Fig. 9) suggest it is inaccurate to assign a slip-rate estimate for a single scarp as representative of vertical displacements for the whole Kern Canyon fault system. As mentioned earlier, per-vasive fracturing common in normal-fault zones can lead to underestimates of total slip.

Late Cenozoic fault reactivation in the south-ern Sierra Nevada confi rms the tendency for mylonitic foliation to be reactivated as normal faults, even when the regional fl ow fi eld is oblique to foliation (e.g., Giorgis et al., 2006). Kern Canyon fault brittle offset localized along preexisting Late Cretaceous ductile shear zones that are oriented north-south (Nadin and Saleeby, 2008; Mahéo et al., 2009). The overprinting of cataclastic and gouge zones on mylonitized gra-nitic and metamorphic basement rocks (Fig. 4) indicates that the mylonitic foliation was re-activated in the brittle regime along the length of the Kern Canyon fault. Geomorphology and seismicity indicate normal-fault reactiva-tion. Other normal faults in the southern Sierra Nevada accommodated Miocene north-south extension attributed to northward migration of a slab window, but these brittle faults are oriented northwest-southeast (see Fig. 1 of Mahéo et al., 2009). Some of these appear to have localized on preexisting Late Cretaceous extensional frac-tures, but the recent activity of the Kern Canyon fault system localized along the northern half of a pervasive ductile shear zone, the proto–Kern Canyon fault. As discussed above, the Kern Canyon fault system was most likely reactivated during regional Miocene exten-sion, even though the fault is oriented north-northeast, obliquely to the north-south–directed Miocene extension. The modern-day southern Sierra Nevada seismogenic fi eld is consistent with east-northeast–west-southwest horizontal extension and vertical crustal thinning (Unruh and Hauksson, 2009). Many north-south–oriented Quaternary faults lie within a 75-km

radius of the Kern Canyon fault zone (Fig. 2B), but the main Kern Canyon fault trace is the only through-going structure with Quaternary offsets that, although discontinuous, are distributed along its entire 130-km length. The other faults are generally less than 20 km long and their off-sets are small or have not yet been measured.

The southern Sierra Nevada south of lati-tude 36.5°N, and the adjacent San Joaquin basin, are characterized by crust that is thin (20–30 km) relative to the ~40-km-thick crust of the central Sierra Nevada (Fliedner et al., 2000). Swarms of extensional earthquakes in the southern Sierra Nevada reveal modern defor-mation within the Sierra Nevada microplate (Jones and Dollar, 1986; Saltus and Lachen-bruch, 1991; Unruh and Hauksson, 2009). Mod-ern deformation has been ascribed to (1) the westward migration of Basin and Range exten-sion (Lockwood and Moore, 1979; Jones and Dollar, 1986; Saltus and Lachenbruch, 1991; Surpless et al., 2002; Niemi, 2003), (2) a shift in transform slip from the San Andreas fault to the Eastern California Shear Zone (Jones et al., 2004), or (3) delamination of the high-density mantle lithosphere from beneath the batholith (Saleeby and Foster, 2004; Unruh and Hauksson , 2009). We fi rst compare the nature of Kern Canyon faulting with patterns related to Basin and Range extension.

The timing of extension in the southern Sierra Nevada is protracted and irregular: early Cenozoic quiescence was followed by a transition from north-south extension to east-west extension in Miocene time and a second episode of east-west extension beginning in Pliocene time. Together with discontinuous,

Figure 9. Oblique aerial view of two paral-lel scarps of the Kern Canyon system, just northeast of the town of Kernville, Califor-nia. White dashed lines indicate fault traces. (For scale, longer dashed line is ~4 km.)



meter-scale Quaternary offsets along the Kern Canyon fault system, this signals that activity along the high-angle Kern Canyon fault sys-tem was punctuated, with two or three discrete episodes of activity over the past ca. 20 Ma. In contrast, Basin and Range–type extension has been migrating steadily northwest along low-angle normal faults since 36 Ma (e.g., Wernicke and Snow, 1998).

The mapped southwestern limit of Basin and Range extension also coincides with two zones of shear that separate it kinematically from the Sierra Nevada microplate to the west. The Eastern California Shear Zone–Walker Lane belt (Fig. 1) is dominated by dextral strike-slip faulting. The Walker Lane seismogenic fi eld indicates northwest-directed dextral strike-slip shear (Unruh and Hauksson, 2009), consistent with faults that accommodate northwest transla-tion of the Sierra Nevada microplate relative to stable North America (e.g., Unruh et al., 2003). Previous studies also suggest that the eastern Sierra Nevada and the adjacent Walker Lane are structurally and kinematically distinct from the Basin and Range to the east (e.g., Wright, 1976; Stewart, 1988; Unruh et al., 2003).

Within the Sierra Nevada frontal fault zone (Fig. 1), Holocene vertical slip rates are 0.2 to 0.3 mm/yr (Le et al., 2007), but dextral slip dominates at ~1.8 mm/yr (Lee et al., 2001). Consistent with mapping and slip-rate analyses of Le et al. (2007), the modern-day strain fi eld is characterized by transtension (Unruh and Hauksson, 2009). Our estimates of vertical slip rate along the Kern Canyon fault have a wide spread at 0.01 to 3.0 mm/yr, but fi eld evidence indicates little to no component of dextral strike-slip displacements along the Quaternary scarps, and seismic evidence also supports exclusively normal dip-slip faulting. Deformation on the Kern Canyon fault thus appears to be decoupled from dextral shear in the Eastern California Shear Zone and transtensional shear along the eastern Sierra range front.

Finally, we consider the geographic and tem-poral distribution of faulting in the southern Sierra Nevada. Miocene transfer faulting along the Kern Canyon fault system in the southwestern Sierra Nevada was followed by Pliocene–Quaternary uplift of the Breckenridge-Greenhorn horst and Quaternary reactivation of the Kern Canyon fault system, which was fol-lowed by the 1983–1984 Durrwood Meadows extensional swarm. These extensional features young to the east. This suggests that deforma-tion is migrating eastward across this part of the batholith, which contrasts with the westward migration of Basin and Range faulting.

We argue here that delamination and surface extension resulting from it is the most likely

cause of recent, west-side-up vertical motion along scarps of the Kern Canyon fault. Exten-sion is commonly linked with basaltic vol-canism in general, and this is seen in the 3.5 Ma fractured lava fl ow in the study area. A Pliocene volcanic pulse in the southern Sierra Nevada has been ascribed to the initiation of mantle lithosphere removal and upwelling of astheno-sphere (e.g., Farmer et al., 2002; Jones et al., 2004). This would be a mantle-driven event that would have thinned the lithosphere and which has invoked predictions of related uplift and ex-tension (e.g., Jones et al., 2004). The semicircu-lar outline of Pliocene volcanism in the Sierra Nevada covers an area from latitudes ~36.6°N to ~38°N, and longitudes ~117.8°W to ~120°W (Manley et al., 2000). This circle is northward of but slightly overlaps the current map projection of the high-velocity anomaly (Fig. 2) that sig-nifi es the descending upper-mantle lithosphere at 70–90-km depth (see Fig. 1 of Gilbert et al., 2007). The map patterns suggest that mantle lithosphere descent began northeast of its cur-rent position. Its descent created a zone of the batholith where the crust is now only ~30 km thick because of mountain root removal, and where asthenosphere has upwelled to replace the delaminated material.

Movement within the southern Sierra Nevada microplate is dominated by horizontal exten-sion and broad uplift. The local phenomenon of upper-mantle horizontal fl ow during the process of mantle lithosphere delamination could pro-duce horizontal extension and vertical thinning in regions adjacent to the descending material (Le Pourhiet et al., 2006). The relatively thin lithosphere (Fliedner et al., 2000) with higher heat fl ow (Saltus and Lachenbruch, 1991) in the southeastern Sierra Nevada may produce asymmetric fl ow that concentrates deformation on the eastern margin of the Isabella anomaly. The zone over which extensional deformation has been resolved lies directly over the Isabella anomaly, the high-velocity anomaly in the upper mantle interpreted to result from convective descent of the Sierra Nevada mantle lithosphere deeper into the mantle (Fig. 2; Benz and Zandt, 1993; Jones et al., 1994; Saleeby et al., 2003; Boyd et al., 2004; Jones et al., 2004; Zandt et al., 2004). This high-velocity domain has been referred to as a “drip” structure because it is cylindrical in shape, ~100 km in diameter, and extends from near the base of the crust to a depth of ~225 km (see Fig. 2 of Saleeby and Foster, 2004). Southern Sierra Nevada topogra-phy suggests that the most recent uplift is related to the ascent of buoyant asthenosphere into the region vacated by the drip as it descends into the deeper mantle beneath the southwestern Sierra Nevada and adjacent San Joaquin basin

(Ducea and Saleeby, 1998; Jones et al., 2004; Saleeby and Foster, 2004; Clark et al., 2005). Depositional patterns in the western Sierra Nevada–San Joaquin basin transition zone indi-cate that a region of accelerated subsidence over-lies the drip (Saleeby and Foster, 2004; Mahéo et al., 2009). Dynamic models of convective instabilities predict such subsidence, as well as coupled uplift marginal to the drip, above the area vacated by the high-density material that sourced the drip (e.g., Pysklywec and Cruden, 2004; Le Pourhiet et al., 2006). These models further predict substantial basement warping along a rolling hinge across the subsidence-marginal up-lift zone, thereby posing a widespread response to mantle processes as an alternative mechanism for the Pliocene–Quaternary phase of activity along the Kern Canyon fault and neighboring structures. The punctuated activity along the Kern Canyon fault could indicate relatively low overall strain that reappeared over a lengthy time interval and localized deformation along a major preexisting structural zone.

CONCLUSIONS

The Kern Canyon fault localized along a Cre-taceous ductile, transpressional shear zone in the southern Sierra Nevada. It was reactivated fi rst during regional early Miocene extension as a transfer structure between two northeast-southwest–extending domains. Normal dip-slip displacement initiated along the Kern Canyon fault in mid-Quaternary time, following locally driven extension, uplift, and volcanism in the southern Sierra Nevada. Several other Quater-nary normal faults of shorter length and smaller displacement developed at the same time, and accommodated westward tilt of the southern part of the batholith. Slip-rate estimates based on scarp-height measurements and GPS verti-cal movements range from ~0.01 to 3.0 mm/yr. The lower estimate places initiation of recent faulting immediately following deposition of a normal-faulted 3.5 Ma lava fl ow at the northern end of the Kern Canyon fault. Field evidence indicates that greater and more frequent dis-placements occurred along the southern part of the Kern Canyon fault, near the Isabella basin, where rupture along the fault has occurred in the past 3.3 ka, and seismic activity continues today. We favor a higher slip rate for the southern part of the Kern Canyon fault, and caution against assigning a single slip rate to the entire length of the fault. Quaternary scarps emerge discontinu-ously or are heavily modifi ed by erosion along its length, suggesting discontinuous rupture.

Normal faulting in the southern Sierra Nevada batholith has migrated eastward since Pliocene time. Modern seismicity segregates

Nadin and Saleeby


active normal faulting along the Kern Canyon fault from active thrust and sinistral strike-slip faulting to the southwest and active dextral strike-slip displacements along the eastern range front and the Eastern California Shear Zone. For these reasons, we suggest that the Kern Canyon fault is responding to local horizontal extension imposed from below by convective removal of the mantle lithosphere beneath the southern Sierra Nevada.

ACKNOWLEDGMENTS

E.N. thanks Ronn Rose of USACE, David Simpson of URS Corporation, and William Page for the heli-copter survey. We thank Carl Tape for seismic data analysis, Nathan Niemi and Ken Hudnut for guidance with GPS data, and Joann Stock for comments. We acknowledge the Southern California Integrated GPS Network and its sponsors, the W.M. Keck Foundation, NASA, National Science Foundation (NSF), U.S. Geological Survey, and Southern California Earth-quake Center, for providing data used in this study. Reviews by David Ferrill, David Peacock, and Erdin Bozkurt improved the content and clarity of this con-tribution. This study was supported by NSF grant EAR-0230383.

REFERENCES CITED

Argus, D.F., and Gordon, R.G., 1991, Current Sierra Nevada–North America motion from very long base-line interferometry: Implications for the kinematics of the Western United States: Geology, v. 19, p. 1085–1088, doi: 10.1130/0091-7613(1991)019<1085:CSN-NAM>2.3.CO;2.

Barosh, P.J., 1969, Use of seismic intensity data to predict the effects of earthquakes and underground nuclear ex-plosions in various geologic settings: U.S. Geological Survey Bulletin B-1279, 93 p.

Bartow, J.A., 1991, The Cenozoic evolution of the San Joa-quin Valley, California: U.S. Geological Survey Profes-sional Paper 1501, 40 p., 2 sheets.

Bartow, J.A., and McDougall, K., 1984, Tertiary stratigra-phy of the southeastern San Joaquin Valley, California: U.S. Geological Survey Bulletin 1529-J, 41 p.

Bawden, G.W., Donnellan, A., Kellogg, L.H., Dong, D., and Rundle, J.B., 1997, Geodetic measurements of hori-zontal strain near the White Wolf Fault, Kern County, California, 1926–1993: Journal of Geophysical Re-search, v. 102, p. 4957–4967, doi: 10.1029/96JB03554.

Bawden, G.W., Michael, A.J., and Kellogg, L.H., 1999, Birth of a fault: Connecting the Kern County and Walker Pass, California, earthquakes: Geology, v. 27, p. 601–604, doi: 10.1130/0091-7613(1999)027<0601:BOAFCT>2.3.CO;2.

Bennett, R.A., Wernicke, B.P., Niemi, N.A., Friedrich, A.M., and Davis, J.L., 2003, Contemporary strain rates in the northern Basin and Range Province from GPS data: Tectonics, v. 22, 31 p.

Benz, H.M., and Zandt, G., 1993, Lithospheric structure of Northern California: Eos (Transactions, American Geophysical Union), v. 74, p. 64.

Blewitt, G., Lavallee, D., Clarke, P., and Nurutdinov, K., 2001, A new global mode of Earth deformation: Sea-sonal cycle detected: Science, v. 294, p. 2342–2345, doi: 10.1126/science.1065328.

Boyd, O.S., Jones, C.H., and Sheehan, A.F., 2004, Founder-ing lithosphere imaged beneath the southern Sierra Nevada, California, USA: Science, v. 305, p. 660–662, doi: 10.1126/science.1099181.

Busby, C., DeOreo, S.B., Skilling, I., Gans, P.B., and Hagan, J.C., 2008, Carson Pass–Kirkwood paleocanyon sys-tem: Paleogeography of the ancestral Cascades arc and implications for landscape evolution of the Sierra

Nevada (California): Geological Society of America Bulletin, v. 120, p. 274–299, doi: 10.1130/B25849.1.

Busby-Spera, C.J., and Saleeby, J.B., 1990, Intra-arc strike-slip fault exposed at batholithic levels in the southern Sierra Nevada, California: Geology, v. 18, p. 255–259, doi: 10.1130/0091-7613(1990)018<0255:IASSFE>2.3.CO;2.

Chester, J.S., 2001, Structure and petrology of the Kern Can-yon Fault, California: A deeply exhumed strike-slip fault: Texas A&M University, Department of Geology and Geophysics.

Clark, M.K., and Farley, K.A., 2007, Sierra Nevada river in-cision from apatite 4He/3He thermochronometry: Eos (Transactions, American Geophysical Union), v. 88, p. F2186.

Clark, M.K., Mahéo, G., Saleeby, J., and Farley, K.A., 2005, The non-equilibrium landscape of the southern Sierra Nevada, California: GSA Today, v. 15, p. 4–10, doi: 10.1130/1052-5173(2005)015[4:TNLOTS]2.0.CO;2.

Clinton, J.F., Hauksson, E., and Solanki, K., 2006, An evalu-ation of the SCSN moment tensor solutions: Robust-ness of the Mw magnitude scale, style of faulting, and automation of the method: Bulletin of the Seismo-logical Society of America, v. 96, p. 1689–1705, doi: 10.1785/0120050241.

Coles, S., Prothero, D.R., Quinn, J.P., and Swisher, C.C., III, 1997, Magnetic stratigraphy of the middle Miocene Bopesta Formation, southern Sierra Nevada, California, in Girty, G.H., Hanson, R.E., and Cooper, J.D., eds., Geology of the western Cordilleran: Perspectives from undergraduate research, Pacifi c Section, Society of Eco-nomic Paleontologists and Mineralogists, v. 82, p. 21–34.

Cox, B.F., and Diggles, M.F., 1986, Geologic map of the El Paso Mountains Wilderness Study Area, Kern County, California: U.S. Geological Survey Miscella-neous Field Studies Map MF-1827, 24 p.

Dalrymple, G.B., 1963, Potassium-argon dates of some Ceno zoic volcanic rocks of the Sierra Nevada: Geologi-cal Society of America Bulletin, v. 74, p. 379–390, doi: 10.1130/0016-7606(1963)74[379:PDOSCV]2.0.CO;2.

Dibblee, T. W., Jr., and Warne, A. H., 1988, Inferred relation of the Oligocene to Miocene Bealville Fanglomerate to the Edison Fault, Caliente Canyon area, Kern County, California: Field Trip Guidebook–Pacifi c Section, SEPM, v. 60, p. 223–231.

Dixon, T.H., Miller, M., Farina, F., Wang, H., and Johnson, D., 2000, Present-day motion of the Sierra Nevada block and some tectonic implications for the Basin and Range Province, North American Cordillera: Tecton-ics, v. 19, p. 1–24, doi: 10.1029/1998TC001088.

Dokka, R.K., and Travis, C.J., 1990, Role of the eastern California shear zone in accommodating Pacifi c-North American plate motion: Geophysical Research Letters, v. 17, p. 1323–1326, doi: 10.1029/GL017i009p01323.

Ducea, M., and Saleeby, J.B., 1998, A case for delamination of the deep batholithic crust beneath the Sierra Nevada, California: International Geology Review, v. 40, p. 78–93, doi: 10.1080/00206819809465199.

Evernden, J.F., Savage, D.E., Curtis, G.H., and James, G.T., 1964, Potassium-argon dates and the Cenozoic mam-malian chronology of North America: American Jour-nal of Science, v. 262, p. 145–198.

Farmer, G.L., Glazner, A.F., and Manley, C.R., 2002, Did lithospheric delamination trigger late Cenozoic potas-sic volcanism in the southern Sierra Nevada, Califor-nia?: Geological Society of America Bulletin, v. 114, p. 754–768, doi: 10.1130/0016-7606(2002)114<0754:DLDTLC>2.0.CO;2.

Fay, N.P., Bennett, R.A., and Hreinsdóttir, S., 2008, Con-temporary vertical velocity of the central Basin and Range and uplift of the southern Sierra Nevada: Geophysical Research Letters, v. 35, p. L20309, doi: 10.1029/2008GL034949.

Fliedner, M.M., Klemperer, S.L., and Cristensen, N.I., 2000, Three-dimensional seismic model of the Sierra Nevada arc, California, and its implications for crustal and upper mantle composition: Journal of Geophysi-cal Research, v. 105, p. 10,899–10,921, doi: 10.1029/2000JB900029.

Gan, W., Svarc, J.L., Savage, J.C., and Prescott, W.H., 2000, Strain accumulation across the eastern Califor-nia shear zone at latitude 36°30′N: Journal of Geo-

physical Research, v. 105, p. 16,229–16,236, doi: 10.1029/2000JB900105.

Gilbert, H., Jones, C., Owens, T.J., and G. Zandt, 2007, Imag ing Sierra Nevada lithospheric sinking: Eos, v. 88, p. 225–229.

Giorgis, S., Tikoff, B., Kelso, P., and Markley, M., 2006, The role of material anisotropy in the neotectonic extension of the Western Idaho shear zone, McCall, Idaho: Geological Society of America Bulletin, v. 118, p. 259–273, doi: 10.1130/B25382.1.

Goodman, E.D., and Malin, P.E., 1992, Evolution of the southern San Joaquin Basin and mid-Tertiary “transi-tional” tectonics, central California: Tectonics, v. 11, p. 478–498, doi: 10.1029/91TC02871.

Greene, D.C., and Schweickert, R.A., 1995, The Gem Lake shear zone; Cretaceous dextral transpression in the northern Ritter Range pendant, eastern Sierra Nevada, California: Tectonics, v. 14, p. 945–961.

Hammond, W.C., and Thatcher, W., 2004, Contemporary tectonic deformation of the Basin and Range Province, western United States: Ten years of observation with the global positioning system: Journal of Geophysical Research, v. 109, 21 p.

Hill, M.L., 1955, Nature of movements on active faults on southern California, in Oakeshott, G.B., ed., Earth-quakes in Kern County, California during 1952: Cali-fornia Division of Mines and Geology Bulletin, v. 171, p. 37–40.

Hilley, G.E., Arrowsmith, J.R., and Amoroso, L., 2001, Inter action between normal faults and fractures and fault scarp morphology: Geophysical Research Letters, v. 28, p. 3777–3780, doi: 10.1029/2001GL012876.

Hirst, B.M., 1986, Infl uence of early Miocene tectonism on Miocene deposystems, Tejon area, Kern County, Cali-fornia: American Association of Petroleum Geologists Bulletin, v. 70, p. 470.

Hunter, L.E., Rose, R.S., and Kelson, K., 2009, Utilization of LiDAR-derived DEMs in assessing geologic hazards near earthen dams in California, USA: Geological So-ciety of America Abstracts with Programs, v. 41, p. 432.

Jones, C.H., Kanamori, H., and Roecker, S.W., 1994, Miss-ing roots and mantle “drips”: Regional Pn and teleseis-mic arrival times in the southern Sierra Nevada and vicinity, California: Journal of Geophysical Research, v. 99, p. 4567–4601, doi: 10.1029/93JB01232.

Jones, C.H., Farmer, G.L., and Unruh, J., 2004, Tectonics of Pliocene removal of lithosphere of the Sierra Nevada, California: Geological Society of America Bulletin, v. 116, p. 1408–1422, doi: 10.1130/B25397.1.

Jones, L.M., and Dollar, R.S., 1986, Evidence of basin-and-range extensional tectonics in the Sierra Nevada: The Durrwood Meadows swarm, Tulare County, California (1983–1984): Bulletin of the Seismological Society of America, v. 76, p. 439–461.

Lawson, A.C., 1904, The geomorphogeny of the upper Kern Basin: University of California Publications in Geo-logical Sciences, p. 291–376.

Le, K., Lee, J., Owen, L.A., and Finkel, R., 2007, Late Qua-ternary 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: Geological Society of America Bulletin, v. 119, p. 240–256, doi: 10.1130/B25960.1.

Le Pourhiet, L., Gurnis, M., and Saleeby, J., 2006, Mantle instability beneath the Sierra Nevada mountains in California and Death Valley extension: Earth and Plan-etary Science Letters, v. 251, p. 104–119, doi: 10.1016/j.epsl.2006.08.028.

Lee, J., Rubin, C.M., and Calvert, A., 2001, Quaternary faulting history along the Deep Springs fault, Califor-nia: Geological Society of America Bulletin, v. 113, p. 855–869, doi: 10.1130/0016-7606(2001)113<0855:QFHATD>2.0.CO;2.

Lin, G., Shearer, P.M., and Hauksson, E., 2007, Applying a three-dimensional velocity model, waveform cross correlation, and cluster analysis to locate southern California seismicity from 1981 to 2005: Journal of Geophysical Research, v. 112, no. B12309, 14 p.

Lockwood, J.P., and Moore, J.G., 1979, Regional deforma-tion of the Sierra Nevada, California, on conjugate micro fault sets: Journal of Geophysical Research, v. 84, p. 6041–6049, doi: 10.1029/JB084iB11p06041.



Lofgren, B.E., and Klausing, R.L., 1969, Land subsidence due to ground-water withdrawal, Tulare-Wasco area, California: U.S. Geological Survey Professional Paper, 437-B, 103 p.

Loomis, D.P., and Burbank, D.W., 1988, The stratigraphic evolution of the El Paso basin, southern California: Im-plications for the Miocene development of the Garlock fault and uplift of the Sierra Nevada: Geological Soci-ety of America Bulletin, v. 100, p. 12–28, doi: 10.1130/0016-7606(1988)100<0012:TSEOTE>2.3.CO;2.

MacPherson, B.A., 1978, Sedimentation and trapping mech-anism in upper Miocene Stevens and older turbidite fans of southeastern San Joaquin Valley, California: American Association of Petroleum Geologists Bul-letin, v. 62, p. 2243–2274.

Mahéo, G., Saleeby, J., Saleeby, Z., and Farley, K.A., 2009, Tectonic control on southern Sierra Nevada topography, California: Tectonics, v. 28, TC6006, doi: 10.1029/2008TC002340.

Manley, C.R., Glazner, A.F., and Farmer, G.L., 2000, Tim-ing of volcanism in the Sierra Nevada of California: Evidence for Pliocene delamination of the batholithic root?: Geol ogy, v. 28, p. 811–814.

Monastero, F.C., Sabin, A.E., and Walker, J.D., 1997, Evidence for post-early Miocene initiation of move-ment on the Garlock fault from offset of the Cudahy Camp Formation, east-central California: Geology, v. 25, p. 247–250, doi: 10.1130/0091-7613(1997)025<0247:EFPEMI>2.3.CO;2.

Moore, J.G., and du Bray, E., 1978, Mapped offset on the dextral Kern Canyon Fault, southern Sierra Nevada, California: Geology, v. 6, p. 205–208, doi: 10.1130/0091-7613(1978)6<205:MOOTRK>2.0.CO;2.

Nadin, E.S., and Saleeby, J.B., 2001, Relationships between the Kern Canyon fault (KCF) and the proto–Kern Can-yon fault (PKCF), southern Sierra Nevada, California: Eos (Transactions, American Geophysical Union), v. 82, p. T32B-0902.

Nadin, E.S., and Saleeby, J.B., 2008, Disruption of regional primary structure of the Sierra Nevada batholith by the Kern Canyon fault system, California, in Wright, J.E., and Shervais, J.W., eds., Ophiolites, Arcs, and Batholiths: Geological Society of America Special Paper 438, p. 429–453.

Niemi, N.A., 2003, Active faulting in the southern Sierra Nevada: Initiation of a new basin-and-range normal fault?: Geological Society of America Abstracts with Programs, v. 35, p. 581.

Nilsen, T.H., Dibblee, T.W., and Addicott, W.O., 1973, Lower and Middle Tertiary stratigraphic units of the San Emigdio and western Tehachapi Mountains, California: U.S. Geological Survey Bulletin 1372-H, p. H1–H23.

Oldow, J.S., Geissman, J.W., and Stockli, D.F., 2008, Evo-lution and strain reorganization within Late Neogene structural stepovers linking the Central Walker Lane and Northern Eastern California Shear Zone, Western Great Basin: International Geology Review, v. 50, p. 270–290.

Page, W., 2005, Assessment of seismic refraction survey at Lake Isabella Auxiliary Dam: Oakland, California, Re-port to URS Corporation for the U.S. Army Corps of Engineers, Sacramento District, September 27, 2005.

Pickett, D.A., and Saleeby, J.B., 1993, Thermobarometric constraints on the depth of exposure and conditions of plutonism and metamorphism at deep levels of the Sierra Nevada Batholith, Tehachapi Mountains, Cali-fornia: Journal of Geophysical Research, v. 98, p. 609–629, doi: 10.1029/92JB01889.

Putirka, K., and Busby, C.J., 2007, The tectonic signifi -cance of high K2O volcanism in the Sierra Nevada, California: Geology, v. 35, p. 923–926, doi: 10.1130/G23914A.1.

Pysklywec, R.N., and Cruden, A.R., 2004, Coupled crust-mantle dynamics and intraplate tectonics: Two-dimensional numerical and three-dimensional analogue

modeling: Geochemistry, Geophysics, Geosystems, v. 748, 22 p.

Ross, D.C., 1986, Basement-rock correlations across the White Wolf–Breckenridge–southern Kern Canyon fault zone, southern Sierra Nevada, California: U.S. Geological Survey Bulletin B-1651, 25 p.

Saleeby, J.B., and Foster, Z., 2004, Topographic response to mantle lithosphere removal in the southern Sierra Nevada region, California: Geology, v. 32, p. 245–248, doi: 10.1130/G19958.1.

Saleeby, J.B., Ducea, M.N., and Clemens-Knott, D., 2003, Production and loss of high-density batholithic root, southern Sierra Nevada, California: Tectonics, v. 22, p. 1–24, doi: 10.1029/2002TC001374.

Saleeby, J., Saleeby, Z., Nadin, E.S., and Mahéo, G., 2009, Stepover in the controlling structure for regional west tilt of the Sierra Nevada microplate–eastern escarp-ment to Kern Canyon system, in Ernst, W.G., ed., Late Cretaceous–Cenozoic topographic evolution of the coupled Sierra Nevada–Basin and Range Physio-graphic Regions: International Geology Review, v. 51, p. 634–669.

Saltus, R.W., and Lachenbruch, A.H., 1991, Thermal evo-lution of the Sierra Nevada: Tectonic implications of new heat fl ow data: Tectonics, v. 10, p. 325–344, doi: 10.1029/90TC02681.

Sella, G.F., Dixon, T.H., and Mao, A., 2002, REVEL: A model for recent plate velocities from space geodesy: Journal of Geophysical Research, v. 107, 17 p.

Sengör, A.M.C., and Burke, K., 1978, Relative timing of rifting and volcanism on Earth and its tectonic implica-tions: Geophysical Research Letters, v. 5, p. 419–421, doi: 10.1029/GL005i006p00419.

Shapiro, N.M., Campillo, M., Stehly, L., and Ritzwoller, M.H., 2005, High-resolution surface-wave tomography from ambient seismic noise: Science, v. 307, p. 1615–1618, doi: 10.1126/science.1108339.

Slade, D.V., Gauger, J., and Vali, V., 1970, Laser inter-ferometer measurement on Kern River fault, in Gauger, J., and Hall, F.F., Jr., eds., Laser Applications in the Geosciences: Huntington Beach, California, Sympo-sium Proceedings, Western Periodicals, p. 163–184.

Stewart, J.H., 1988, Tectonics of the Walker Lane Belt, west-ern Great Basin: Mesozoic and Cenozoic deformation in a zone of shear, in Ernst, W.G., ed., Rubey Collo-quium on Metamorphism and Crustal Evolution of the Western United States: Rubey Volume, v. 7, p. 683–713.

Stock, G.M., Anderson, R.S., and Finkel, R.C., 2004, Pace of landscape evolution in the Sierra Nevada, Califor-nia, revealed by cosmogenic dating of cave sediments: Geol ogy, v. 32, p. 193–196, doi: 10.1130/G20197.1.

Surpless, B., 2008, Modern strain localization in the cen-tral Walker Lane, western United States: Implications for the evolution of intraplate deformation in transten-sional settings: Tectonophysics, v. 457, p. 239–253, doi: 10.1016/j.tecto.2008.07.001.

Surpless, B.E., Stockli, D.F., Dumitru, T.A., and Miller, E.L., 2002, Two-phase westward encroachment of Basin and Range extension into the northern Sierra Nevada: Tectonics, v. 21, no. 1, p. 1002, doi: 10.1029/2000TC001257.

Tan, Y., 2006, Broadband waveform modeling over a dense seismic network [Ph.D. thesis]: Pasadena, California, California Institute of Technology, 157 p.

Taylor, T.R., Dewey, J.F., and Monastero, F.C., 2008, Transtensional deformation of the brittle crust; field observations and theoretical applications in the Coso–China Lake region, eastern margin of the Sierra Nevada microplate, southeastern California: International Geology Review, v. 50, p. 218–244, doi: 10.2747/0020-6814.50.3.218.

Thatcher, W., Foulger, G.R., Julian, B.R., Svarc, J.L., Quilty, E., and Bawden, G. W., 1999, Present-day deformation across the Basin and Range Province, Western United States: Science, v. 283, p. 1714–1718.

Tikoff, B., and Greene, D.C., 1994, Transpressional defor-mation within the Sierra Crest shear zone system, Sierra Nevada, California (92–80 Ma): Vertical and horizontal stretching lineations within a single shear zone: Geological Society of America (Abstracts with Programs), v. 26, p. 385.

Tikoff, B., and Saint Blanquat, M., 1997, Transpressional shearing and strike-slip partitioning in the Late Cre-taceous Sierra Nevada magmatic arc, California: Tec-tonics, v. 16, p. 442–459.

Tobisch, O.T., Saleeby, J.B., Renne, P.R., McNulty, B., and Tong, W.X., 1995, Variations in deformation fi elds during development of a large-volume magmatic arc, central Sierra Nevada, California: Geological Society of America Bulletin, v. 107, p. 148–166.

Townley, S.D., and Allen, M.W., 1939, Descriptive cata-logue of earthquakes of the Pacifi c Coast of the United States, 1769 to 1928: Bulletin of the Seismological So-ciety of America, v. 29, p. 1–297.

Treasher, R.C., 1949, Kern County fault, Kern County, Cali-fornia: Geological Society of America Bulletin, v. 60, p. 1958.

Unruh, J., Humphrey, J., and Barron, A., 2003, Transten-sional model for the Sierra Nevada frontal fault sys-tem, eastern California: Geology, v. 31, p. 327–330, doi: 10.1130/0091-7613(2003)031<0327:TMFTSN>2.0.CO;2.

Unruh, J.R., and Hauksson, E., 2009, Seismotectonics of an evolving intracontinental plate boundary, southeastern California, in Oldow, J.S., and Cashman, P.H., eds., Late Cenozoic Structure and Evolution of the Great Basin–Sierra Nevada Transition: Geological Society of America Special Paper 447, p. 351–372.

Vali, V., Krogstad, R.S., Moss, R.W., and Engel, R., 1968, Some observations of strains across the Kern River fault using laser interferometer: Journal of Geo-physical Research, v. 73, p. 6143–6147, doi: 10.1029/JB073i018p06143.

Wakabayashi, J., and Sawyer, T.L., 2001, Stream incision, tectonics, uplift, and evolution of topography of the Sierra Nevada, California: The Journal of Geology, v. 109, p. 539–562, doi: 10.1086/321962.

Webb, G.W., 1981, Stevens and earlier Miocene turbidite sandstones, southern San Joaquin Valley, California: American Association of Petroleum Geologists Bul-letin, v. 65, p. 438–465.

Webb, R.W., 1936, Kern Canyon fault, southern Sierra Nevada : The Journal of Geology, v. 44, p. 631–638, doi: 10.1086/624459.

Webb, R.W., 1946, Geomorphology of the middle Kern River basin, southern Sierra Nevada, California: Geo-logical Society of America Bulletin, v. 57, p. 355–382, doi: 10.1130/0016-7606(1946)57[355:GOTMKR]2.0.CO;2.

Wernicke, B., and Snow, J.K., 1998, Cenozoic tectonism in the central Basin and Range: Motion of the Sierran–Great Valley Block: International Geology Review, v. 40, p. 403–410, doi: 10.1080/00206819809465217.

Wright, L., 1976, Late Cenozoic fault patterns and stress fi elds in the Great Basin and westward displacement of the Sierra Nevada Block: Geology, v. 4, p. 489–494, doi: 10.1130/0091-7613(1976)4<489:LCFPAS>2.0.CO;2.

Zandt, G., Gilbert, H., Owens, T.J., Ducea, M., Saleeby, J., and Jones, C.H., 2004, Active foundering of a conti-nental arc root beneath the southern Sierra Nevada in California: Nature, v. 431, p. 41–46, doi: 10.1038/nature02847.

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