Slip rates on the Fish Springs fault, Owens Valley, California,
deduced from cosmogenic 10Be and 26Al and soil
development on fan surfaces
Paul H. Zehfuss*
Department of Geology, Humboldt State University, Arcata, California 95521, USA
Paul R. Bierman
Department of Geology, University of Vermont, Burlington, Vermont 05405, USA
Alan R. Gillespie
Department of Geological Sciences, University of Washington, Seattle, Washington 98195, USA
Raymond M. Burke
Department of Geology, Humboldt State University, Arcata, California 95521, USA
Marc W. Caffee
Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94550, USA
ABSTRACT
Long-term deformation along the Fish
Springs fault in Owens Valley, California,
is recorded by offset landforms, including a
previously dated cinder cone (39Ar/40Ar, 314
6 36 ka, 2s), several debris-flow fans and
levees deposited by Birch Creek, stream
channels, and lava flows of nearby Crater
Mountain. The 10Be and 26Al model exposure ages (n 5 68) delimit fan ages and suggest that deposition stopped after ca. 136,
15, 13, and 8 ka. One fan remains active
and has undergone deposition throughout
the Holocene. Soil development on three
fans, where boulders were sampled for 10Be
and 26Al analysis, also indicates distinct
ages. Together, soil development and cosmogenic isotope data suggest that fan deposits correlate with the Tahoe and late
Tioga glaciations. Soil profile development
index values from Fish Springs are low
compared with those determined elsewhere,
*Present address: Department of Geological Sciences, University of Washington, Seattle, Washington 98195; e-mail: [email protected].
1
GSA Data Repository item 2001xx, PD1 values for soil pits and cosmogenic ages for nearest
sampled boulders, is available on the Web at http:
//www.geosociety.org/pubs/ft2001.htm. Requests
may also be sent to Documents Secretary, GSA,
P.O. Box 9140, Boulder, CO 80301; e-mail:
[email protected].
suggesting relatively slow rates of soil formation for fan surfaces at Fish Springs
and/or modification of soil profiles by surface processes during or following soil formation. Age estimates and measured offsets
of the fans are consistent with a long-term
vertical slip rate of 0.24 6 0.04 m k.y.–1 for
the Fish Springs fault over the past 300 k.y.
Keywords: fans, faulting, isotopes, Owens
Valley, soils.
INTRODUCTION
Debris-flow fan deposits in Owens Valley,
along the eastern base of the Sierra Nevada,
provide data that record displacement along
the dominant structure, the Owens Valley fault
zone. Fan deposition along the Sierra Nevada
has been linked to periods of glaciation (Gillespie, 1982). Because fan deposition is episodic, it is possible to assign meaningful age
ranges to fan surfaces, which at Fish Springs
are dissected and offset by faults.
The Fish Springs fault is 10 km south of
Big Pine, California, between the Sierra Nevada and Inyo Ranges (Fig. 1). The fault displaces debris-flow fan surfaces deposited by
Birch Creek, active and abandoned stream
channels, a cinder cone, and lava flows of Crater Mountain (Figs. 2 and 3). The Fish Springs
fault is a strand of the predominantly right-
lateral Owens Valley fault zone, but is distinct
from the main fault trace in two ways: (1) displacement at Fish Springs appears to be solely
vertical (Martel et al., 1987, 1989), and (2) the
fault strikes due north as opposed to N208W,
the average strike of the 110-km-long Owens
Valley fault zone (Beanland and Clark, 1994).
The entire 110 km length of the Owens Valley fault zone last ruptured in the earthquake
of March 26, 1872, which is thought to have
measured near 8.0 on the Richter scale. The
Fish Springs fault also probably ruptured during the earthquake of 1872, locally producing
vertical displacements of ;1 m (Martel, 1984;
Beanland and Clark, 1994).
Martel et al. (1987, 1989) measured offsets
and estimated displacement rates at Fish
Springs. In their study, relative-weathering
criteria were used to correlate fans of different
ages with nearby glacial deposits exhibiting
similar degrees of weathering. Existing data
on the timing of Sierra Nevada glacial maxima
were used to estimate the ages of displaced
fan surfaces. One fan, offset 3.3 6 0.3 m, was
correlated by Martel et al. (1987) to the Tioga
glaciation (oxygen isotope stage 2). Another
fan, offset 31 6 3 m, was correlated with the
Tahoe glaciation (oxygen isotope stage 4 or
6). The cinder cone is displaced 76 6 8 m and
has a 39Ar/40Ar age of 314 6 36 ka (2s; Martel
et al., 1987). On the basis of these data, Martel
et al. (1989) calculated the average late Qua-
GSA Bulletin; February 2001; v. 113; no. 2; p. 000–000; 11 figures; 5 tables.
For permission to copy, contact Copyright Clearance Center at www.copyright.com
q 2001 Geological Society of America
ZEHFUSS et al.
Figure 1. Generalized map showing location of the Owens Valley fault zone. Location of study area is shown by box. Fault
location is from Beanland and Clark
(1994).
ternary displacement rate for the Fish Springs
fault as 0.24 6 0.04 m k.y.–1.
Advancements in numerical and relative
dating techniques have improved our ability
to estimate the ages of geologic surfaces. The
accumulation of cosmogenic isotopes results
from the interaction of cosmic rays with materials at the Earth’s surface. Using assumed
rates of isotope production, the exposure age
of a surface can be estimated from the abundance of cosmogenic isotopes preserved in the
surface material (Lal, 1988). In situ2produced
cosmogenic isotopes have been used in Owens
Valley to estimate directly the timing of debris-flow fan deposition near Lone Pine (Fig.
1; Bierman et al., 1995a). To define the ages
of fan surfaces deposited at Fish Springs, we
measured cosmogenic 10Be and 26Al produced
in quartz extracted from 34 granitic boulder
samples (Table 1).The 10Be and 26Al data enable estimation of faulting rates using direct
age estimates of the offset fan surfaces. They
also allow us to determine whether faulting
rates have been constant or whether they have
varied over the past 300 k.y.
Soil development is useful as a mapping
tool and provides rough estimates of surface
age. Indices quantifying the degree of soil development (Harden, 1982; Harden and Taylor,
1983) provide a relative means of dating of
geomorphic features, but detailed investigations of well-dated soil chronosequences have
not been published for Owens Valley fans. We
Figure 2. (A) Geologic map of Fish Springs fault, debris fan units, cinder cone, lava
from Crater Mountain, and other landforms superimposed on aerial photograph (134-15 from BLM CA01-77, 9/30/77). Locations of soil pits are shown by rectangles.
Contacts are dashed where uncertain. Bar and ball are on relative downthrown side.
The location of scarp profile L on the west fan is shown in white. Remaining scarp
profiles are shown in Figure 4A. (B) Cosmogenic sample sites. Letters correspond with
samples listed in Table 1.
used the profile development index (PDI) of
Harden (1982) to quantify the degree of soil
development in 11 soil pits (Table A1). Although soils do not provide direct estimates of
fan surface age, they confirm the relative age
differences defined by the fan units and compliment the cosmogenic age estimates by
showing how processes at the surface may
have influenced boulder exposure.
METHODS
Previous study at Fish Springs by Martel et
al. (1987) and Martel (1984) provided a map
of the fault and fan surfaces based on relative
differences in surface weathering. Three fans,
the west, north, and south, were mapped. Our
work introduces additional fan units and detail
to the map of Martel et al. (1987) (Fig. 2A).
Mapping
Fan units were differentiated by observing
variations in relative boulder weathering,
crosscutting relations, and clast lithology (Fig.
2A). Different degrees of weathering on fan
boulders (such as flaking and rock varnish development) as well as differences in the de-
Geological Society of America Bulletin, February 2001
SLIP RATES ON THE FISH SPRINGS FAULT, OWENS VALLEY, CALIFORNIA
Figure 2. Continued
gree of fan surface soil reddening helped us
to distinguish fans of different relative ages.
The lithology of boulder- and cobble-size debris was used to differentiate fan units; some
fans (north fans B and C, Fig. 2A) contain
distinctive volcanic and metamorphic lithologies among abundant granitic clasts. Analysis
of aerial photographs augmented the field
work.
Cosmogenic Dating
Sampling and Sample Preparation
We sampled 34 granitic boulders from fans
for analysis of in situ2produced 10Be and 26Al
(Fig. 2B). We sampled one boulder twice
(FSF-V; Table 1) to assess the reproducibility
of our analyses. Boulder sample FSF-I had insufficient quartz for analysis. Samples were
collected from the upper 124 cm of boulders
using a hammer and chisel. Boulders for sampling were selected on the basis of shape and
size; where possible, we sampled those with
flat tops, diameters .1 m, and heights .1 m
above the ground surface. Sites suggesting
complex erosion and burial histories were
avoided. Sample sites were marked on aerial
photographs and 1:24 000 U.S. Geological
Survey topographic maps. A Garmin 75 global positioning system (GPS) was used to locate sample sites to within ;20 m.
Preparation for sample analysis involved
isolating and purifying quartz through density
separation and acid-etching of crushed samples (Kohl and Nishiizumi, 1991). Following
dissolution of 30245 g of quartz in hydrofluoric acid (HF), multiple inductively coupled
argon plasma spectrometer2optical emission
(ICP-OE) analyses of the HF solution were
used to determine the abundance of stable Al.
A Be carrier (250 mg) was added prior to dissolution. Fe was removed using anion exchange. Ti was removed by pH-specific precipitation. Be and Al were separated using
cation exchange, precipitated as hydroxides,
and converted to oxides. BeO and AlO3 were
mixed with Ag and packed in targets for analysis. Accelerator mass spectrometric (AMS)
analysis of samples to determine isotope ratios
was performed at Lawrence Livermore National Laboratory. Ratios were normalized to
internal standards prepared by Nishiizumi. Extraction and target preparation were carried
out at the University of Vermont.
Data Reduction and Age Modeling
Cosmogenic ages are estimated using interpretive models. Although the analysis of cosmogenic nuclide abundance in a particular
sample may be both precise and accurate,
translation of these data into reliable estimates
of age depends on the accuracy of the production rate and the validity of age-model assumptions. While it appears increasingly likely that actual production rates are less than
those proposed by Nishiizumi et al. (1989)
(Clark et al., 1995; Larsen, 1996; Stone et al.,
1998), we have chosen to calculate our ages
with the rates of Nishiizumi et al. (1989) (Table 1), 6.03 (10Be) and 36.8 (26Al) atoms g–1
yr–1, because such calculations allow us to
compare our ages directly with those calculated by others. We also calculate ages using
the production rates of Larsen (1996) (Table
1), 5.17 (10Be) and 30.4 (26Al) atoms g–1 yr–1,
following the recent acceptance of lower production rates. At this time, production rates
are not known with certainty, nor do we know
which of the different production rate estimates is correct. Additional uncertainties in
site-specific nuclide production rates result
from altitude and latitude corrections needed
to normalize production rates and the production induced by muons (Brown et al., 1995),
which we assumed to be zero. We scaled production rates for altitude and latitude using
spallation-only normalization of Lal (1991).
Inheritance, or prior exposure of a sampled
surface to cosmic rays, leads to higher than
expected abundances of cosmogenic nuclides.
Boulders on fan surfaces at Fish Springs may
have experienced inheritance as a result of prior exposure in moraines, higher portions of
the fan surfaces, or on the mountain front. Our
model for fan surface dating using cosmogenic nuclides assumes that at the time of deposition boulders on fan surfaces contained no
10
Be and 26Al.
Erosion from boulder surfaces attenuates
the concentration of cosmogenic isotopes, thus
reducing the apparent age of the sample. Bierman et al. (1995b) calculated erosion rates
ranging from 0.4 to 0.9 cm k.y.–1 for granitic
rock in Alabama Hills ;60 km south of Fish
Springs. The maximum erosion rate allowed
by the concentrations of cosmogenic isotopes
we measured in the oldest boulders (from west
fan) at Fish Springs is 0.4 cm k.y.–1. Considering this rate as an upper limit, we propose
that 0.2 6 0.1 cm k.y.–1 is a reasonable estimate of erosion rates on Fish Springs boulders. Table 1 provides erosion-corrected age
estimates assuming an erosion rate of 0.2 6
0.1 cm k.y.–1. Erosion-corrected ages were cal-
Geological Society of America Bulletin, February 2001
ZEHFUSS et al.
Figure 3. (A) Fish Springs fault displacing the fans (w—west fan, n—north fan group, s—south fan) and cinder cone (cc). Photo is
looking northwest toward Crater Mountain (in background). (B) Fish Springs fault displacing the cinder cone. Photo is looking south
toward Poverty Hills (in background). Scarp on north fan B deposits (nB) and mouth of abandoned channel are seen in the foreground.
Figure 4. (A) Map showing scarp profile locations
(enlargement of Fig. 2A). Profile L, to the south, is
shown in Figure 2A. (B) Scarp profiles A (north fan
A), H (north fan C), and L (west fan). (C) Technique
to calculate vertical separation (vs) and vertical displacement (vd) shown for all profiles in Table 2. Vertical displacements calculated assuming a fault dip
of 598 (taken from Martel, 1984). Fan surface slope
ranges from 28 to 48 among profiles.
Geological Society of America Bulletin, February 2001
SLIP RATES ON THE FISH SPRINGS FAULT, OWENS VALLEY, CALIFORNIA
Figure 5. (A) Sampled boulder FSF-Y, west fan (140 6 28 ka). Boulder is very weathered and fractured. (B) Sampled boulder FSFAG, south fan (3.8 6 0.7 ka). Boulder is fresh and is exposed well above the fan surface (.1 m).
culated using the model of Nishiizumi et al.
(1991),
N
1
5
(1 2 e2( l1re L21 )t )
P
(l 1 reL21 )
(1)
where N 5 nuclide concentration, P 5 production rate, r 5 average rock density (2.7 g
cm–3), L5 absorption mean free path (165 g
cm–2), l 5 decay constant of the radionuclide
(4.6 3 10–7[10Be] and 9.9 3 10–7[26Al]), and t
5 time. By assuming a constant rate of erosion (e 5 0.2 6 0.1 cm k.y.–1), the erosioncorrected age of a sample was estimated by
solving for time (t). Maximum and minimum
limits of erosion corrected ages were calculated using the quadratic sum of erosion-rate uncertainty and analytic error of individual
samples.
We assigned an error to our age estimates
based on measurement uncertainties. Uncertainties in the scaling of exposure altitude and
latitude, as well as magnetic-field variation
over time, affect the calculated ages systematically. We assume that uncertainties in measured isotope abundance, prior exposure history, and boulder erosion affect model age
calculations randomly.
We estimate the exposure age of each sampled boulder by calculating weighted averages
of individual 10Be and 26Al measurements (Table 1). Weighted averages were calculated
using
xwav 6 swav 5
Owx 6 1
Ow Ow
!
i
i
(2)
i
i
where xwav 5 weighted average of sample, wi
5 (1/si2), xi 5 individual Be and Al measurements, and si 5 measurement error (Taylor,
1982). Weighted averages of boulders from
the same fans were averaged arithmetically (6
one standard deviation) to calculate fan age
(Table 1).
Soil Development
We excavated 11 soil pits using a backhoe
at sites on three (of five) different fan surfaces.
Sites were located on the same surfaces sampled for cosmogenic dating in an attempt to
reveal stratigraphic relations among different
fan units based on soil properties. Detailed
field descriptions of soil horizons and soil
properties were made using standard nomenclature (Soil Survey Staff, 1975; Birkeland,
1984). Soil properties were described, sampled, and analyzed by Zehfuss to standardize
the descriptions. Samples collected from each
horizon were analyzed for particle size at
Humboldt State University using settling
tubes and sieves (Singer and Janitzky, 1986).
We used the PDI (Harden, 1982; Harden
and Taylor, 1983) to quantify soil development in each soil pit (Appendix 1). PDI values
were calculated using the four soil properties
shown by Harden and Taylor (1983) to be
most strongly correlated with age: clay films,
rubification, texture, and dry (or moist) consistence. Properties described from the lowermost C horizons in each pit were used to
characterize the parent material. Depth normalization has a minimal effect on PDI values
in our study because the Cox horizons were
used as the parent materials, yielding index
values of 0 for those horizons. A negative
consequence of using the Cox horizon in lieu
of a single parent material is that profile index
values may be too low, because the assumed
Cox values of 0 may not accurately depict the
degree of development. One benefit of using
the Cox horizon as the parent material is that
we account for differences in sedimentological
characteristics among deposits by relating soil
properties directly to the material on which the
soils are formed.
Harden and Taylor (1983) demonstrated
that the PDI is an effective tool for describing
soil development with respect to age because
rates of development for many soil properties
are similar in different climate zones. We
compared PDI values generated from this
study with those from Harden and Taylor
(1983) and Slate (1996) in order to contrast
rates of soil development on fans at Fish
Springs with rates observed elsewhere.
Fault Scarp Profiles
Scarp profiles (A though K) were made at
11 locations along the main trace of the Fish
Springs fault using total station survey equipment (Fig. 4A). Profile L, shown in Figure 2A,
and profile M (Fig. 4A) characterize the morphology of a smaller scarp located ;200 m
west of the main trace. The slope of the original, unfaulted fan surface (a) was identified
on both sides of the fault and was used to
estimate vertical separation (Fig. 4, B and C).
Martel (1984) estimated the dip of the Fish
Springs fault as 598 to the east. Vertical displacements were calculated assuming that the
Fish Springs fault has a dip of 598 (Fig. 4C;
Table 2).
Geological Society of America Bulletin, February 2001
ZEHFUSS et al.
RESULTS AND INTERPRETATIONS
Each fan at Fish Springs represents multiple
episodes of debris-flow and stream deposition
and consists of complex assemblages of levees, channels, and channel fills. The fan surfaces are composed of large granitic boulders
(to ;4 m in diameter), gravel, and sand.
Channel walls and road cuts provide crosssectional views of the fan sediments, exposing
debris flows to a few meters thick that bury
older deposits, some capped with well-developed soils. Four major faulted fan units, located both north and south of the cinder cone,
were identified in this study. A fifth fan unit
(the youngest, s in Fig. 2) emanates from
modern Birch Creek, and does not appear to
have been offset, or its surface has been modified since offset. Our fan map (Fig. 2) differs
somewhat from that of Martel et al. (1987),
primarily in the lateral extent and subdivision
of the north fan. Where units are similar, their
nomenclature has been maintained.
Fan Units
Patterns of deposition for the fans at Fish
Springs have been influenced by the fault, cinder cone, and channels eroded into the fan surfaces. The oldest fan units make up a large
proportion of the total fan surface area near
the fault. Young fan units have filled channels
incised into older fan surfaces on the upthrown block, and spread out over the surface
of the downthrown block (Fig. 2A). The most
recent deposition has been limited to a fan east
of the fault and south of the cinder cone.
Fan Units West of Scarp
The west fan unit represents the oldest and
most heavily weathered of the faulted fan
units. Its discolored surface appears reddish
on aerial photographs (Fig. 2A) and in the
field. Variable degrees of weathering across
the surface suggest a complex history of erosion and sedimentation. Large boulders are infrequent, and some are heavily weathered,
having elephant-skin texture and heavy varnish coatings (Fig. 5A). Subparallel channels,
oriented east-west, have eroded the surface of
the west fan, forming swales in the topography, which in some places have been filled by
subsequent debris flows. The most prominent
channel at Fish Springs is the modern stream
channel of Birch Creek. The stream has incised deeply the west fan, forming a broad,
meandering channel that continues east of the
fault scarp and south of the Fish Springs cinder cone.
Incision of the west fan by Birch Creek and
Figure 6. 26Al and 10Be model exposure ages for 34 samples. Ages were calculated using
production rates of Nishiizumi et al. (1989) assuming zero erosion. Error bars reflect
uncertainty in ages, propagating only counting statistics, blank, and carrier uncertainties.
Fan units are identified by letters (Fig. 2B).
Figure 7. PDI (soil profile development index) values and maximum clay percent in the
B horizons of soils from the south fan, north fan A, and the west fan. PDI values generally
increase with age. Age control from average 10Be and 26Al age estimates for the nearest
boulders (Appendix 1) was calculated using production rates of Nishiizumi et al. (1989),
assuming an erosion rate of 0.2 6 0.1 cm k.y.21.
Geological Society of America Bulletin, February 2001
SLIP RATES ON THE FISH SPRINGS FAULT, OWENS VALLEY, CALIFORNIA
TABLE 1. COSMOGENIC ISOTOPE DATA FOR FISH SPRINGS DEBRIS FAN BOULDERS
Sample
26
Map
Be
Al
elevation*
measured
measured
6
21 †
6
(m)
(10 atom g ) (10 atom g21)†
10
West fan
FSF-X
1280
1.55 6 0.04
9.28 6 0.50
FSF-Y
1285
1.74 6 0.05
9.19 6 0.42
FSF-Z
1290
1.26 6 0.03
8.09 6 0.38
FSF-AA
1290
1.63 6 0.06
10.11 6 0.49
FSF-AB
1315
1.53 6 0.06
8.77 6 0.40
FSF-AC
1307
1.75 6 0.05
11.87 6 0.54
FSF-AD
1303
1.58 6 0.04
10.37 6 0.48
FSF-AE
1300
1.53 6 0.04
9.48 6 0.43
Arithmetic mean of sample ages 6 1 standard deviation
North fan A
Group 1
FSF-A
1264
0.22 6 0.01
1.24 6 0.07
FSF-B
1265
0.18 6 0.01
1.04 6 0.05
FSF-C
1265
0.17 6 0.01
0.94 6 0.05
FSF-D
1256
0.19 6 0.01
1.15 6 0.06
FSF-E
1255
0.20 6 0.01
1.17 6 0.05
FSF-F
1256
0.18 6 0.01
1.20 6 0.06
FSF-U
1250
0.20 6 0.02
1.26 6 0.15
FSF-V1**
1261
0.19 6 0.01
1.24 6 0.06
FSF-V2**
1261
0.18 6 0.01
1.18 6 0.06
FSF-W
1261
0.17 6 0.01
1.19 6 0.07
Arithmetic mean of sample ages 6 1 standard deviation
Group 2
FSF-M
1239
0.26 6 0.01
1.64 6 0.08
FSF-O
1239
0.27 6 0.01
1.74 6 0.08
Arithmetic mean of sample ages 6 1 standard deviation
Group 3
FSF-N
1239
0.41 6 0.01
2.54 6 0.12
FSF-T
1256
0.42 6 0.02
2.62 6 0.14
Arithmetic mean of sample ages 6 1 standard deviation
Al/10Be
Production rates of Nishiizumi et al. (1989)
26
Be
model age§
(k.y.)
10
Al
model age§
(k.y.)
Production rates
of Larsen (1996)
Be and 26Al
Average age# (ky)
26
10
Zero
erosion
0.2 6 0.1 cm k.y.21
erosion
10
Be and 26Al
Average age# (ky)
Zero
erosion
0.2 6 0.1 cm k.y.21
erosion
5.98
5.30
6.40
6.22
5.73
6.79
6.56
6.19
6
6
6
6
6
6
6
6
0.36
0.29
0.35
0.37
0.33
0.36
0.35
0.33
105.6
118.1
84.0
111.4
103.2
118.1
109.3
103.6
106.7
6
6
6
6
6
6
6
6
6
2.9
3.6
2.3
3.9
3.8
3.3
2.9
2.8
10.9
106.5
105.1
90.4
117.2
99.3
136.7
121.7
108.2
110.6
6
6
6
6
6
6
6
6
6
5.7
.8
4.3
5.7
4.5
6.2
5.6
4.9
14.3
105.8
113.4
85.4
113.3
101.6
122.1
111.9
104.7
107.3
6
6
6
6
6
6
6
6
6
2.9
3.6
2.3
3.9
3.8
3.3
2.9
2.8
10.9
133.5
140.2
103.3
146.3
125.8
161.9
145.3
132.6
136.1
6
6
6
6
6
6
6
6
6
19.9
28.1
10.8
23.7
19.1
28.0
22.0
18.9
17.2
125.0
135.1
100.9
134.5
121.6
144.3
132.2
123.9
127.2
6
6
6
6
6
6
6
6
6
3.4
4.2
2.7
4.5
4.4
3.8
3.4
3.3
12.9
168.5
181.3
127.2
184.1
160.4
196.4
180.1
166.1
170.5
6
6
6
6
6
6
6
6
6
32.5
48.7
16.3
39.4
30.6
48.4
36.6
30.5
20.9
5.64
5.75
5.51
6.10
5.84
6.59
6.39
6.57
6.48
7.06
6
6
6
6
6
6
6
6
6
6
0.42
0.49
0.47
0.48
0.46
0.49
0.89
0.47
0.54
0.57
14.8
12.4
11.9
13.0
13.6
12.6
13.3
12.8
12.4
11.5
12.8
6
6
6
6
6
6
6
6
6
6
6
0.7
0.8
0.8
0.7
0.8
0.7
1.0
0.6
0.8
0.7
0.9
13.7
11.7
10.8
13.0
13.0
13.6
14.0
13.8
13.2
13.4
13.0
6
6
6
6
6
6
6
6
6
6
6
0.8
0.6
0.5
0.7
0.6
0.7
1.6
0.7
0.6
0.7
1.0
14.3
12.0
11.1
13.0
13.2
13.1
13.5
13.3
12.9
12.4
12.9
6
6
6
6
6
6
6
6
6
6
6
0.7
0.8
0.8
0.7
0.8
0.7
1.0
0.6
0.8
0.7
0.9
14.7
12.2
11.3
13.3
13.5
13.4
13.8
13.5
13.2
12.7
13.2
6
6
6
6
6
6
6
6
6
6
6
0.8
0.8
0.8
0.8
0.9
0.7
1.1
0.6
0.8
0.7
0.9
17.0
14.3
13.3
15.4
15.9
15.6
15.9
15.7
15.4
14.7
15.3
6
6
6
6
6
6
6
6
6
6
6
0.8
1.0
1.0
0.8
1.0
0.8
1.2
0.7
1.0
0.8
1.0
17.5
14.7
13.7
15.9
16.3
16.0
16.3
16.1
15.8
15.1
15.7
6
6
6
6
6
6
6
6
6
6
6
0.9
1.1
1.1
1.0
1.1
0.9
1.3
0.8
1.1
0.9
1.0
6.33 6 0.43
6.51 6 0.39
18.0 6 0.9
18.6 6 0.7
18.3 6 0.4
18.7 6 0.9
19.9 6 1.0
19.3 6 0.9
18.3 6 0.9
19.0 6 0.7
18.7 6 0.5
19.0 6 1.0
19.7 6 0.8
19.3 6 0.5
21.8 6 1.0
22.5 6 0.8
22.1 6 0.5
22.6 6 1.2
23.4 6 1.0
23.0 6 0.6
6.28 6 0.37
6.24 6 0.44
28.0 6 1.0
28.0 6 1.2
28.0 6 0.1
29.0 6 1.4
28.9 6 1.6
28.9 6 0.1
28.3 6 1.0
28.4 6 1.2
28.3 6 0.1
29.9 6 1.4
29.9 6 1.6
29.9 6 0.1
33.4 6 1.1
33.6 6 1.4
33.5 6 0.1
35.6 6 1.7
35.8 6 1.9
35.7 6 0.1
North fan C
FSF-R††
1255
0.33 6 0.02
2.00 6 0.10
FSF-S
1255
0.21 6 0.01
1.37 6 0.07
FSF-P1
1255
0.18 6 0.01
1.30 6 0.08
FSF-Q
1255
0.20 6 0.01
1.24 6 0.07
Arithmetic mean of sample ages 6 1 standard deviation
6.08
6.48
7.30
6.14
6
6
6
6
0.43
0.39
0.63
0.49
22.4
14.6
12.6
14.0
13.7
6
6
6
6
6
1.1
0.5
0.7
0.8
1.1
22.5
15.6
15.1
14.1
15.0
6
6
6
6
6
1.1
0.8
1.0
0.8
0.8
22.5
15.0
13.5
14.1
14.2
6
6
6
6
6
1.1
0.5
0.7
0.8
0.7
23.4
15.3
13.7
14.4
14.5
6
6
6
6
6
1.3
0.6
0.7
0.9
0.8
26.7
17.7
16.0
16.7
16.8
6
6
6
6
6
1.3
0.6
0.9
0.9
0.9
28.1
18.3
16.4
17.2
17.3
6
6
6
6
6
1.6
0.7
1.0
1.0
0.9
North fan B
FSF-G
1256
0.15 6 0.01
0.89 6 0.04
FSF-H
1246
0.09 6 0.01
0.51 6 0.03
FSF-J
1249
0.11 6 0.01
0.77 6 0.05
FSF-L
1246
0.11 6 0.01
0.70 6 0.04
FSF-K††
1249
0.35 6 0.01
2.10 6 0.11
Arithmetic mean of sample ages 6 1 standard deviation
5.95
5.97
6.81
6.08
5.97
6
6
6
6
6
0.42
0.63
0.78
0.55
0.36
10.3
5.8
7.8
7.8
24.3
7.9
6
6
6
6
6
6
0.5
0.5
0.7
0.5
0.8
1.8
10.1
5.7
8.7
7.8
23.9
8.1
6
6
6
6
6
6
0.5
0.3
0.6
0.4
1.2
1.8
10.2
5.8
8.3
7.8
24.2
8.0
6
6
6
6
6
6
0.5
0.5
0.7
0.5
0.8
1.8
10.4
5.8
8.4
7.9
25.3
8.1
6
6
6
6
6
6
0.5
0.5
0.7
0.5
1.1
1.9
12.1
6.9
9.9
9.3
28.5
9.6
6
6
6
6
6
6
.6
0.6
0.8
0.6
1.0
2.1
12.4
7.0
10.1
9.5
30.1
9.7
6
6
6
6
6
6
0.6
0.6
0.8
0.6
1.4
2.2
South fan
FSF-AF
FSF-AG
FSF-AH
1260
1259
1260
0.10 6 0.01
0.05 6 0.01
0.02 6 0.01
0.65 6 0.04 6.60 6 0.60
0.29 6 0.02 5.98 6 1.16
0.13 6 0.02 6.58 6 3.13
6.6 6 0.5
3.2 6 0.6
1.4 6 0.6
7.2 6 0.4
3.1 6 0.2
1.5 6 0.3
6.9 6 0.5
3.2 6 0.6
1.5 6 0.6
7.1 6 0.5
3.2 6 0.6
1.5 6 0.6
8.3 6 0.5
3.8 6 0.7
1.8 6 0.7
8.3 6 0.5
3.8 6 0.7
1.8 6 0.7
*Map elevation used for production rate calculation.
†
Errors include isotope ratio, blank, and carrier uncertainties.
§
Errors on individual 10Be and 26Al estimates reflect only analytic uncertainty.
#10
Be and 26Al average ages are weighted averages of 10Be and 26Al model ages for each sample. Average ages were calculated assuming zero erosion and 0.2 6 0.1
cm k.y.21 erosion from boulder surfaces. The erosion rate error of 0.1 cm k.y.21 is compounded with analytic error of individual samples.
**Replicate samples from different location on top of one boulder.
††
Model ages not included in calculation of average surface exposure ages.
Geological Society of America Bulletin, February 2001
ZEHFUSS et al.
migration of the creek channel north of the
cinder cone provided a series of conduits for
the deposition of a suite of north fans, termed
collectively in this paper as the north fan
group. West of the fault, the younger north fan
deposits are easily distinguished from the west
fan; the younger deposits are rough and bouldery in comparison. Exposed north fan boulders are less weathered and sit prominently on
the surface (Fig. 5B). In some areas, deposits
of the north fan group are a veneer on the
thicker west fan, appearing in road cuts, channel walls, and trenches as 122-m-thick strata
overlying older buried soils. In places, isolated
boulders of the younger, north fan group overlie heavily weathered boulders of the west fan.
Fan Units East of the Scarp
Fan surfaces east of the scarp were created
during periods of repeated fault displacements, permitting debris flows passing
through the upthrown block to escape the confinement of channels and form coalescing fans
on the downthrown block. Here, the distinction among members of the north fan group
becomes clearer. In order of decreasing relative age, the fans east of the scarp are north
fans C and A, north fan B, and south fan.
Debris flows composing north fan C were
channeled through basalt from Crater Mountain, resulting in a fan surface containing
large, angular, locally derived basaltic boulders in addition to granitic boulders from the
Sierra Nevada. Granitic boulders are as much
as 2 m in diameter and are moderately
weathered.
North fan A is the largest fan in the north
fan group. Its surface is characterized by moderately weathered boulders (diameter #4 m)
that are flaking and have well-developed varnish. The degree of boulder weathering of north
fan A is comparable to that of north fan C.
North fan B represents the last member of
the northern fan group to be built by Birch
Creek before the active channel was diverted
to the south, where it is today. An abandoned
channel, incised into north fan A west of the
scarp, provided a path for the water and debris
that shaped north fan B. The topography is
rough; the surface is littered with cobbles and
boulders forming distinct levees on both sides
of the channel east of the fault. Variability in
weathering and cosmogenic ages (Table 1) of
exposed boulders suggests that material from
previous deposits may have been reworked
and incorporated into this fan. Basalt clasts
derived from Crater Mountain are found in the
north fan B deposits, providing a lithologic
distinction from north fan A, immediately to
the north.
TABLE 2. SCARP PROFILE DATA FOR THE FISH SPRINGS FAULT
Profile
A†
B†
C†
D†
E§
F
G
H
I
J#
K
L
M
Vertical
separation
(m)
Vertical
displacement
(m)*
3.9
3.2
3.7
3.5
4.3
1.0
1.5
2.7
3.2
0.5?
18.6
2.5
1.6
4.0
3.3
3.8
3.6
4.5
1.0
1.5
2.8
3.3
0.5
19.3
2.6
1.7
Location
North fan A
North fan A
North fan A
North fan A
North fan B, levee
Channel of north fan
North fan B, levee
North fan C
North fan C
Channel of north fan
Lava
West fan, west of main
West fan, west of main
B
C
fault
fault
*Calculated as shown in Figure 4C assuming a fault dip of 598 (Martel,1984)
†
Surface gradient on upthrown side was used to reconstruct the prefaulting fan surface. Downthrown surface
has steeper gradient probably due to draping of an existing scarp at the time of deposition (Fig. 9).
§
Levee appears to drape a preexisting scarp in addition to being faulted. Actual amount of displacement could
not be determined. Vertical separation and vertical displacement are probably overestimates.
#
Scarp is not clearly defined. Small step in topography up channel may represent a nick point.
The south fan is the youngest fan at Fish
Springs. Its apex is where the fault intersects the
modern channel of Birch Creek, which has incised the west fan. Like north fan B, the south
fan is mapped only east of the fault, on the
downthrown block. The surface is cobbly and
contains large (diameter #4 m) fresh boulders
deposited near the apex. Birch Creek continues
to play an active role in the morphologic development of the fan. A trench dug in the middle
to distal portions of the fan (trench 6; Fig. 2A)
revealed a complex fluvial and mudflow stratigraphy, and at least one buried soil. Neither our
mapping nor that of Martel (1984) has identified
a continuation of the Fish Springs fault scarp in
the south fan, indicating that the fan surface has
not been offset significantly since the most recent deposition.
Immediately south of the cinder cone is a
flat surface intermediate in height between the
west and south fan surfaces. The surface,
termed the tread, is bounded on the west by
the main Fish Springs fault and on the east by
another east-dipping fault striking northeast.
Debris shed from the western scarp has accumulated on the tread, forming small colluvial wedges at the break in slope.
Cosmogenic Nuclide Model Ages
Model 10Be and 26Al ages from boulders on
different fans vary from a few thousand years
to older than 100 ka (Table 1). These ages
reflect accumulation of nuclides and are interpreted here as the minimum duration of exposure of boulders sampled at the fan surface,
and represent the timing of debris-flow deposition (Table 3).
The 10Be and 26Al model ages are well cor-
related (Fig. 6), yielding an r2 value of 0.988.
Regression analysis indicates 26Al/10Be for this
data set is 6.12, consistent with prior estimates
(Nishiizumi et al., 1989). Replicate samples
from the top surface of boulder FSF-V have statistically inseparable 10Be concentrations (0.19 6
0.01 and 0.18 6 0.01 3 106 atoms g–1) and 26Al
abundances (1.24 6 0.06 and 1.18 6 0.06 3
106 atoms g–1; Table 1). The reproducibility of
these analyses and the strong correlation between ages calculated using both isotopes indicate that the variability in boulder ages on the
same surface results from factors other than analytic uncertainties. For most surfaces, age variability between boulders exceeds analytic uncertainty, implying that differences between
boulder ages result from geologic processes such
as time- transgressive deposition, periods of
boulder burial and exposure, inheritance, and/or
erosion.
Cosmogenic 10Be and 26Al age estimates in
combination with geomorphic data from this
study permit delineation of seven boulder
populations (Table 1). Eight boulders sampled
from the west fan have weighted average
model ages (10Be and 26Al) from 103 to 162
ka, assuming an erosion rate of 0.2 6 0.1 cm
k.y.–1. The mean model age and standard deviation are 136 6 17 ka. Cosmogenic age estimates for the west fan are significantly affected by the erosion correction (;30% older)
while ages for the younger fans change little
(,3% older) (Table 1).
Ages from north fan A cluster into three
distinct groups (Table 1). The 10 boulders of
group 1 range in weighted average model age
from 11.3 to 14.7 ka, assuming an erosion rate
of 0.2 6 0.1 cm k.y.–1. The mean age and
standard deviation are 13.2 6 0.9 ka (n 5 10).
Geological Society of America Bulletin, February 2001
SLIP RATES ON THE FISH SPRINGS FAULT, OWENS VALLEY, CALIFORNIA
We take this result to be the time of abandonment of the faulted portion of north fan A because it incorporates a large boulder population and because the sampled boulders in this
group are near the fault scarp where the age
of the faulted surface is probably best represented. Boulders from group 2 (FSF-M, FSFO) of north fan A have model ages and standard deviations of 19.0 6 1.0 ka and 19.7 6
0.8 ka. Boulders from group 3 (FSF-N, FSFT) of north fan A have model ages and standard deviations of 29.9 6 1.4 ka and 29.9 6
1.6 ka. These more heavily dosed boulders are
located at the margins of north fan A, where
contacts with other fans to the north and south
form low points in the topography. Boulders
in groups 2 and 3 probably represent outcrops
of older debris flows that were buried by
younger deposits containing boulders composing group 1. Age estimates from boulder
groups 2 and 3 are not included in the calculation of displacement rates because we cannot confidently assign vertical displacements
to these two fan surfaces.
Exposure ages for three boulders on north
fan C, assuming an erosion rate of 0.2 6 0.1
cm k.y.–1, range from 13.7 to 15.3 ka, with a
mean and standard deviation of 14.5 6 0.8 ka
(n 5 3). A fourth boulder, FSF-R, has an average model exposure age of 23.4 6 1.3 ka,
much greater than the other boulders examined from this surface, possibly a result of inheritance. This boulder was not included in
the calculation of average fan surface age. Age
estimates for north fan C are not statistically
distinct from north fan A.
North fan B contains the youngest boulders
of the north fan group. The fan is dissimilar
to other deposits at Fish Springs; boulders on
its surface are weathered to different degrees,
and are generally smaller and better rounded
than boulders from north fans A and C. Calculated model ages assuming an erosion rate
of 0.2 6 0.1 cm k.y.–1 range from 5.8 to 10.4
ka, with a mean of 8.1 6 1.9 ka (n 5 4). The
variability in boulder weathering and model
boulder ages for this fan is likely a result of
the reworking of older fan strata. Boulder
FSF-K has an estimated age of 25.3 6 1.1 ka,
and is significantly older than other boulders
sampled from north fan B, probably a result
of prior exposure. FSF-K was not included in
the calculation of average fan exposure age.
South fan boulders range in model age from
1.5 to 7.1 ka (n 5 3), assuming an erosion
rate of 0.2 6 0.1 cm k.y.–1. Boulders sampled
from this surface are fresh, very large, and tall
(tops as much as 2 m above the fan surface).
Boulder ages were not combined into an average for this surface because the ages prob-
TABLE 3. SUMMARY OF AGE AND DISPLACEMENT DATA FOR GEOMORPHIC UNITS AT FISH SPRINGS
Martel et al. (1987)
Unit
This study
Unit
(k.y.)
Relative age
(k.y.)
Relative Age
(k.y.)*
Cinder cone
West
West
North fan C
North fan
Tahoe
Stage 4 or Stage 6
§
65–75
128–195§
Tioga
10.6–26†
Tahoe
Stage 6
135–210#
Tioga
15–25#
North fan A
North fan
North fan B
North fan
South fan
South fan
Holocene
Tioga
10.6–26†
Holocene
Numerical age
(m)
Displacement
314 6 36†
76 6 8†
136 6 17
(171 6 21)
14.5 6 0.9
(17.3 6 0.9)
13.2 6 1.0
(15.7 6 1.0)
8.1 6 1.9
(9.7 6 2.2)
7.1, 3.2, 1.5
(8.3, 3.8, 1.8)
31 6 3†
3.1 6 0.4**
3.7 6 0.3**
1.3 6 0.3**
unfaulted
*Ages (except for cinder cone) are average model exposure ages and standard deviation calculated using
production rates of Nishiizumi et al. (1989) and Larsen (1996) (in parentheses) assuming an erosion rate of
0.260.1 cm ky21.
†
Ar-Ar age and displacement of Martel et al. (1987).
§
Birkeland et al.,1971; Smith, 1979; Atwater et al., 1986; Mezger and Burbank, 1986 (cited in Martel et al.,1987).
#
Ages from Gillespie and Molnar (1995). Correlation of Tahoe with stage 6 after Burke and Birkeland (1979).
**Average and standard deviation for displacement measurements in Table 2. Displacements in profiles J and E
(Table 3) are excluded from average displacements of north fans C and B (respectively) calculated for this table.
ably represent multiple periods of debris-flow
deposition. Variability could also be the result
of inheritance.
Soil Development and Weathering
Soil profiles reveal significant differences in
the degree of weathering between the fans.
Field observations and laboratory analysis of
soil profiles from the west fan, north fan A,
and the south fan indicate distinct ages for
each deposit (Appendix 1). PDI values and
maximum clay percents in the B horizon increase with increasing fan age, as estimated
by relative weathering of fan surfaces, crosscutting relations, separation of tectonically
offset surfaces, and cosmogenic exposure age
estimates of the nearest sampled boulders
(Appendix 1; Figs. 7 and 8).
Soils developed on the west fan are easily
distinguished from the younger north fan and
south fan soils on the basis of subsurface
boulder weathering, reddening, and the presence of a Bt horizon having elevated clay content (Appendix 1; Fig. 8). However, results
from field, laboratory, and PDI calculations
for the three sites on the west fan are variable
(Appendix 1; Fig. 7). Clay films were identified in only two of three west fan pits, and a
significant degree of reddening (to 7.5YR hue)
was detected in just one of the profiles. Although each of the soils described on this surface contains a Bt horizon, laboratory analysis
revealed maximum clay percents ranging from
17.5% to 32.7% (Appendix 1). PDI values
also have a broad range (2.9218.4), primarily
reflecting variation in clay films and
rubification.
Six soils studied on north fan A are moderately developed (Appendix 1). Typically, the
profiles have Bw horizons (with the exception
of a Bt horizon in soil 7) with a modest increase in clay percents relative to upper and
lower horizons (Fig. 8). Unlike the west fan
soils, clay films are absent from north fan A
profiles, and boulder and cobble disintegration
in the subsurface is minimal. The degree of
reddening is noticeably less in soils of north
fan A than in soils of the west fan. Probably
the most conspicuous difference between soils
formed on the two surfaces is the degree of
variability in soil development (Fig. 7). Much
variability is observed in the group of west fan
sites, whereas north fan A soils are relatively
similar. Soil PDI values for north fan A range
from 2.2 to 3.7, and maximum clay percents
range from 5.4% to 11.4% (Appendix 1). The
consistency of soils data from north fan A is
similar to the consistency of cosmogenic age
estimates of group 1 on the same fan surface.
Soil pit 9, dug into the surface of north fan
A near the cinder cone (Fig. 2A), revealed a
well-developed buried B horizon (Appendix
1). The degree of development as well as
proximity to the west fan surface suggest that
the west fan soil is shallowly buried by the
younger north fan A deposit.
Soil pit 6 dug into the surface of the south
fan exposed two buried soils in stratified fluvial and debris-flow deposits (Fig. 8). The uppermost soil is developed in a layer of fluvial
deposits and has a PDI value of 0 (Appendix
1). This layer was probably deposited recently
by localized stream activity (Fig. 2A). The
buried horizons are in debris-flow deposits
Geological Society of America Bulletin, February 2001
ZEHFUSS et al.
and have PDI values of 1.5 (b) and 4.0 (b2).
We used the PDI of the uppermost buried horizon (1.5) to estimate soil development because our cosmogenic age control comes from
large boulders that were probably deposited
during debris-flow deposition rather than
stream deposition. The PDI for the lowest buried horizon (4.0) is similar to values calculated for north fan A (2.223.8), and suggests
that a fan surface similar in age to north fan
A may be buried by younger south fan
deposits.
Vertical Displacements
At its midpoint, near the cinder cone, the
Fish Springs fault scarp attains its greatest displacement. The scarp gradually decreases in
height on both sides of the cinder cone, eventually pinching out in the lavas of Crater
Mountain 2 km to the north and in alluvium
abutting Poverty Hills 2 km to the south. Our
scarp profiles are located within 1 km of the
cinder cone, where we assume that the displacement gradient is minimal.
The vertical displacements of the cinder
cone (76 6 8 m) and west fan (31 6 3 m)
were determined by Martel et al. (1987, 1989).
The current study presents vertical displacements of the three north fan units not differentiated in previous investigations (Table 2).
In addition, we present vertical displacements
of lava flows from Crater Mountain and along
a fault in the west fan located west of the main
trace (Fig. 2). The scarps we measured are discussed in the following in order of youngest
to oldest.
Profiles F and G (Table 2; Fig. 4A) from
north fan B have displacements of 1.0 m and
1.5 m, respectively. The 1.0 m of vertical displacement from profile F surveyed in the offset abandoned channel is consistent with a
measurement of 1.1 m made by Martel et al.
(1987). The scarp in profile G is also about
1.0 m in height, and probably represents the
amount of offset since the deposition of north
fan B, probably that of one earthquake.
Profile E, from a prominent levee in north
fan B, shows a vertical displacement of 4.5 m
(Table 2). In profile E, a preexisting scarp is
draped by a levee that is faulted. We are unable to distinguish how much of the 4.5 m of
scarp height is a result of fault slip postdating
the deposition of north fan B. Consequently,
profile E is not included the estimates of vertical displacement for north fan B.
In several profiles from north fan A (profiles A2D), the slopes on either side of the
fault are not consistent (Fig. 4B, profile A).
The slope of the downthrown side (;98) for
these profiles is steeper than that of the upthrown side (;38). We interpret the discrepancy in slopes to indicate that deposits constituting the surface in these profiles drape a
preexisting fault scarp (Fig. 9). Alternatively,
this morphology may have been produced
when debris flows escaped the confinement of
channels incised into the upthrown block,
forming a steep fan apex as they spilled onto
the downthrown block. In such cases, the
slope of the upthrown side (28248) was used
to extend a surface from the base of the portion of the scarp, which we interpreted to represent postdepositional displacement (Fig. 4,
B and C). The vertical separation between this
surface and that of the upthrown block was
used to estimate vertical displacement.
Profiles A through D from north fan A reveal vertical displacements ranging from 3.3
to 4.0 m (Table 2). Although it is possible that
the technique used to account for apparent
draping of the deposits over a preexisting
scarp may have led to underestimates of displacement of as much as a few meters, an average displacement and standard deviation of
3.7 6 0.3 m for north fan A measurements is
consistent with the measurements of 3.3 6 0.3
m of Martel et al. (1987) at the same location.
Two scarps are apparent in the profiles from
north fan C (Fig. 4B, profile H). The location
of the Fish Springs fault is marked by a scarp
displacing the levees of north fan C. A second
scarp, 15 m to the west, elevates lava ;5 m
above the fan deposits. Two profiles on the
north fan C levees indicate vertical displacements of 2.8 m (Fig. 4B, profile H) and 3.3
m (profile I) (Table 2). A small step in topography (0.5 m) in the abandoned channel of
north fan C (profile J; Table 2) may represent
a nick point. To the north, the Fish Springs
fault vertically displaces lava flows (Fig. 2) by
19.3 m (profile K, Fig. 4A; Table 2).
Profiles L (Fig. 2A) and M (Fig. 4B) indicate vertical displacements of 2.6 and 1.7 m,
and were measured across a fault located west
of the main trace in the west fan (Table 2).
The scarp is heavily degraded, indicating old
age, or possibly draping by west fan deposits.
The fault does not displace the younger deposits of north fans A or C, implying that it
has not been active since their deposition.
Slip Rates
The average vertical slip rate along the Fish
Springs fault over the past 314 k.y. is 0.24 6
0.04 m k.y.–1, assuming the production rates
of Nishiizumi et al. (1989) and a boulder erosion rate of 0.2 6 0.1 cm k.y.–1 (Table 4; Fig.
10). Using the production rates of Larsen
(1996) and the same erosion rate, the average
vertical slip rate over the same interval is 0.23
10.04/–0.03 m k.y.–1 (Table 4).
Considering only the fan data, and correcting for erosion, the average vertical slip rate
over the past 1402170 k.y. is 0.23 6 0.03 m
k.y.–1 (using production rates of Nishiizumi et
al., 1989) or 0.18 10.04/–0.03 m k.y.–1 (using
the production rates of Larsen, 1996) (Table
4; Fig. 10). For the interval between the formation of the cinder cone and west fan
(3142140 ka), the average vertical slip rate is
0.25 10.14/–0.06 m k.y.–1 (using production
rates of Nishiizumi et al., 1989) or 0.31
10.21/–0.08 m k.y.–1 (using the production
rates of Larsen, 1996) (Table 4; Fig. 10).
DISCUSSION: SOIL DEVELOPMENT
AND COSMOGENIC DATA
The accuracy of our slip-rate estimates depends on the accuracy of our estimates of fan
surface age. Landform surfaces can be unstable and vulnerable to modification. Thus, we
consider how techniques used to date surfaces
have been influenced by surface-modifying
processes. The first part of the discussion reviews how soil and cosmogenic data correlate
with one another and with data from other
studies. We consider how soil development
and cosmogenic data sets together provide
clues about the postdepositional history of
Fish Springs fan surfaces.
Correlation of Soil Development with
Other Chronosequences
We compare our PDI values, calibrated using cosmogenic ages, with those calculated for
soils developed at five other sites investigated
by Harden and Taylor (1983) and Slate (1996).
The sites and climates studied by Harden and
Taylor are: Merced, California (xeric-inland);
Ventura, California (xeric-coastal); Las Cruces, New Mexico (aridic); and Susquehanna
Valley, Pennsylvania (udic). Slate (1996) calculated PDI values for fan surfaces in Fish
Lake Valley (aridic), about 60 km northeast of
Fish Springs. We compare our values with the
six-property index calculated by Slate (1996),
including clay films, rubification, texture, dry
consistence, color lightening, and secondary
carbonate. The climate of Owens Valley is
semiarid.
PDI values from this study are lower than
PDI values for similar age soils investigated
by Harden and Taylor (1983) (Fig. 11). A primary reason for lower PDI values at Fish
Springs may be differences in rates of soil for-
Geological Society of America Bulletin, February 2001
SLIP RATES ON THE FISH SPRINGS FAULT, OWENS VALLEY, CALIFORNIA
Figure 8. Pedologic distinctions
between soil pits of different
ages, including depth and types
of soil horizons, and change in
clay percents through the profiles. Lowercase b preceded by
a number indicates sequential
buried horizons.
mation between sites. Climate and eolian dust
influx change over time and space and significantly affect rates of soil development (Bockheim, 1980; McFadden and Weldon, 1987).
With the exception of Las Cruces, Fish
Springs is drier than the other sites studied by
Harden and Taylor (1983), leading to slower
rates of soil development. Modern dust-flux
rates at Las Cruces (Gile et al., 1981) are
much higher than rates measured within 10
km of Fish Springs by Reheis (1997), providing an explanation for the discrepancy in soil
development rates between these two sites.
Differences in geomorphic surfaces on
which the soils are developed affect dust- trapping efficiency. Parent materials for soils from
the four different climatic regimes studied by
Harden and Taylor (1983) were unconsolidated alluvial fan and fluvial deposits. Debrisflow deposits at Fish Springs are generally
well consolidated and poorly sorted. Lower
infiltration rates of water and eolian silt in the
debris-flow deposits at Fish Springs possibly
led to slow soil-formation rates in comparison
to more gravel-rich substrates elsewhere.
PDI values from this study are also lower
than those calculated by Slate (1996) for soils
formed in a similar climate on similar parent
materials (Fig. 9). The lower PDI values for
Fish Springs suggests that factors aside from
differences in climate and parent material are
influencing rates of soil development at Fish
Springs. The proximity of the soil pit locations to the fault scarp (Fig. 2A) could have
made them more vulnerable to increased erosion than other portions of the fan surfaces.
The subsequent removal of soil constituents
would result in soils that appear younger than
expected.
Correlation of Soil Development and
Cosmogenic Age Estimates
Soil development among sample sites in the
west fan is highly variable, while cosmogenic
age estimates for boulder samples are much
less variable. Soils appear underdeveloped for
their estimated age when compared with other
data sets (i.e., Harden and Taylor, 1983; Slate,
1996). Conversely, cosmogenic ages seem to
correspond well with the anticipated Tahoe
age for the west fan surface.
Discrepancies between characteristics of
soil PDI and cosmogenic data from the west
fan may be explained by degradation of the
original surface morphology and by the position of sample sites relative to geomorphic
features such as the Fish Springs fault scarp
and other landforms common to debris-flow
surfaces in Owens Valley, such as levees,
channels, and terraces. Degradation of these
features over time by processes such as soil
creep, bioturbation, slope wash, and rain
splash (Whipple and Dunne, 1992) serves to
redistribute material and weathering products
and ultimately smooth the fan surface.
Boulders sampled for cosmogenic analysis
on the west fan may have been buried or ex-
posed by the same processes of surface aggradation and degradation that affected the soils.
The variability of cosmogenic data may be explained by differences in the position of sampled boulders relative to a degrading landform, such as the fault scarp. The lesser scatter
in boulder ages than in soil development probably reflects the greater resistance of boulders
to translocation and erosion. Further, we sampled large boulders in an effort to minimize
the impact of local surface processes on exposure ages.
DISCUSSION: SLIP RATES
Integrated over 300 k.y., the average vertical slip rate for the Fish Springs fault is 0.24
6 0.04 m k.y.–1 (Table 4; Fig. 10). Slip rates
calculated using fan ages estimated using the
production rates of Larsen (1996) (Table 4;
Fig. 10) are also consistent with a long-term,
integrated slip rate of 0.24 6 0.04 m k.y.–1
(Table 4).
A linear relationship between displacement
and surface age is consistent with our data
when they are interpreted using the rates of
Nishiizumi et al. (1989), implying that if the
production rates are correct, the rate of vertical
displacement has been constant, or nearly so,
since formation of the cinder cone at 314 ka
(Fig. 10; Table 4). However, the estimated
west fan age calculated using the production
rates of Larsen (1996) and an erosion rate of
0.2 6 0.1 cm k.y.–1 affects the displacement-
Geological Society of America Bulletin, February 2001
ZEHFUSS et al.
Figure 9. Progression of events resulting in
different surface slopes on either side of
fault. Stage 1 shows a faulted surface. At
stage 2, fan deposition buries the fault
scarp. In stage 3, a displacement event
breaks the young, wedge-shaped deposit.
age relationship (Fig. 10) sufficiently to suggest that rates have varied over the past 314
k.y. (Table 4). Thus, slip rates calculated by
this study are sensitive to age model assumptions including production rates, erosion, and
the relevance of mean boulder ages to actual
fan age, particularly when considering the age
of the west fan. In addition, about 200 k.y.
years elapsed between the formation of the
cinder cone and west fan, during which slip
rates may have varied significantly.
The relation of slip rates calculated for the
Fish Springs fault to those determined for the
Owens Valley fault zone is difficult to assess.
Beanland and Clark (1994) used vertical and
right-lateral slip measured for the 1872 earthquake near Lone Pine (Lubetkin and Clark,
1987, 1988) and other sites to suggest that an
average ratio of 6:1 described the relative
components of horizontal:vertical motion
along the fault zone during that event. They
applied the 6:1 ratio to the vertical displacement determined by Martel et al. (1989) at
Fish Springs to estimate horizontal slip for the
fault zone there, cautioning a large degree of
uncertainty. Martel et al. (1987) and Beanland
and Clark (1994) found no horizontal slip on
the Fish Springs fault. The main trace of the
Owens Valley fault zone immediately east of
the Fish Springs fault is assumed to accommodate all of the horizontal strain at that location along the fault zone (Beanland and
Figure 10. Estimated vertical slip rates for the Fish Springs fault. Uncertainties in vertical
displacement and cosmogenic age are shown. Ages calculated using production rates of
Nishiizumi et al. (1989) assuming an erosion rate of 0.2 6 0.1 cm k.y.21 are shown as bold
error bars, and the integrated slip rate determined using those ages is indicated as the
slope of the solid line. Ages calculated using the production rates of Larsen (1996) and
assuming an erosion rate of 0.2 6 0.1 cm k.y.21 are shown as thin error bars, and slip
rates (from fan data, and cinder cone and west fan data) are indicated by the slope of the
dashed lines. Also shown are mean ages for the west fan calculated using both sets of
production rates assuming zero erosion.
TABLE 4. DISPLACEMENT RATES FOR THE FISH SPRINGS FAULT
Unit interval
Production rates of Nishiizumi et al. (1989)
Production rates of Larsen (1996)
Time interval
(k.y.)
Displacement rate*
(m k.y.–1)
Time interval
(k.y.)
Displacement rate*
(m k.y.–1)
Integrated rate (all data)†
314 to 0
0.24 6 0.04
314 to 0
Integrated rate (fan data)§
136 to 0
0.23 6 0.03
171 to 0
314 to 136
0.25 1 0.14
0.25–0.06
314 to 171
0.23 1 0.04
0.23–0.03
0.18 1 0.04
0.18–0.03
0.31 1 0.21
0.31–0.08
Cinder cone to west fan
*Errors on displacement rates were calculated using a Monte Carlo simulation (1s).
†
Includes ages and displacements of cinder cone and fans.
§
Includes ages and displacements of all fans.
Clark, 1994). Accepting this assumption, we
calculate an average rate of 1.4 m k.y.–1 of
horizontal slip rate for the Owens Valley fault
zone in the Fish Springs vicinity based on our
fan ages. This rate is similar to the rate of 1.5
m k.y.–1 calculated by Beanland and Clark
(1994) and is also consistent with the 0.722.2
m k.y.–1 strike-slip rate reported by Lubetkin
and Clark (1988) for the Owens Valley fault
zone.
CONCLUSIONS
The 10Be and 26Al data from this study support the interpretation that significant sedimentation on Fish Springs fan surfaces occurred during Sierra Nevada glaciations. The
ages of north fans A and C, 13 and 15 ka,
appear to correlate with the Tioga glaciation,
ca. 15225 ka (Gillespie and Molnar, 1995).
The age of the west fan, estimated as
Geological Society of America Bulletin, February 2001
SLIP RATES ON THE FISH SPRINGS FAULT, OWENS VALLEY, CALIFORNIA
Figure 11. PDI (soil profile development index) values from this study (regression line 1)
and Harden and Taylor (1983) and Slate (1996) (regression line 2) versus numeric age.
Error bars are shown for ages and/or Log10(PDI) values from Slate (1996) and this study
because we chose to present average and standard deviation of multiple measurements.
PDI values from Fish Springs soils are lower than the others, probably reflecting differences in rates of soil development and/or soil erosion.
1032162 ka, may correspond with the older
Tahoe (stage 6) glaciation, ca. 1352210 ka
(Burke and Birkeland, 1979; Gillespie and
Molnar, 1995). The degree of boulder weathering on the west fan surface is similar to that
of nearby Tahoe glacial deposits.
Ages from the south fan suggest that deposition on fans at Fish Springs is not strictly
limited to glacial periods, although the volume
of Holocene deposits is small. Large, fresh
boulders on the surface suggest that large debris flows have funneled through the southern
Birch Creek channel, forming the south fan
during the Holocene. Modern stream activity
and fluvial stratigraphy on the south fan demonstrate that isolated fan surfaces are now being eroded, at least locally. Similar activity
has occurred on fans investigated near Lone
Pine (Lubetkin and Clark, 1988; Bierman et
al., 1995a).
The 10Be and 26Al estimates of fan exposure
ages at Fish Springs are similar to age estimates for other Owens Valley fans, suggesting
that fan-building episodes may be linked in
time. Bierman et al. (1995a) measured 10Be
and 26Al in boulders on fans near Lone Pine,
part of a glaciated drainage 60 km to the
south. The surface exposure age of a Lone
Pine fan (Qg1) similar in size and degree of
weathering to the west fan is 98.2 6 30.1 ka
(10Be) and 67.3 6 18.8 ka (26Al), using production rates of Nishiizumi et al. (1989) and
assuming zero boulder erosion. The age of another Lone Pine fan interpreted by Lubetkin
and Clark (1988) to be correlated with the Tioga glaciation is 11.6 6 3.7 ka (10Be) and 11.7
6 3.6 ka (26Al). This age is similar to ages of
north fans A and C, 13 and 15 ka. The Lone
Pine fan Qg3 of Bierman et al. (1995a) has an
age of ca. 25 ka, similar to ages for the much
smaller north fan A groups 2 and 3, 19 and
30 ka. Thus, at Fish Springs, a significant volume of older fan sediments may be concealed
by the younger north fans B and C, and north
fan A, group 1.
The 10Be and 26Al model ages for Fish
Springs fans provide direct numerical age estimates for a soil chronosequence that we used
to calibrate PDI values. The wide scatter of
PDI values, especially on the west fan, suggests that the relation of PDI values with age
at Fish Springs is highly variable and that the
PDI is not a reliable indicator of age here. The
soils and cosmogenic data indicate that rates
of soil development on Fish Springs fans are
slow, as previously suggested for soils developed on the east side of the Sierra Nevada
mountains (Birkeland, 1990; Berry, 1994).
Comparison of Fish Springs soils with those
developed on moraines of the Tahoe glaciation
(Burke and Birkeland, 1979; Berry, 1994; La
Farge, 1997) indicates that higher quantities of
clay are present in B horizons on the west fan
surfaces than on correlative moraines. Several
possible explanations for this contrast are that
(1) rates of eolian influx are greater on the
fans because they are at lower elevations closer to the source of dust; (2) the particle-size
distributions of the parent material are different, with a larger proportion of fine material
in the debris-flow deposits compared to till;
(3) erosion has stripped more soil away from
the moraine surfaces than the fan surfaces; and
(4) the moraines are younger than the fans.
Our calculated displacement rate of 0.24 6
0.04 m k.y.–1 for the Fish Springs fault over
the past 300 k.y. is identical to the previous
estimate of Martel et al. (1989). We have
made this estimate more robust by dating the
surfaces of the fans directly rather than assigning ages on the basis of correlation of the
fans with glacial periods. Long-term vertical
displacement rates of 0.3 6 0.1 m k.y.–1 at Big
Pine, and 0.4 6 0.1 m k.y.–1 near Lone Pine,
were calculated by Martel et al. (1987) using
the bedrock displacement along the Owens
Valley fault zone as determined by Pakiser et
al. (1964). These rates are only slightly higher
than the rate calculated for the Fish Springs
fault in this study.
Although we acknowledge the large time
gaps in our analysis of slip rates, we suggest
that the constancy of faulting rates indicated
by our data provides important information
about the character of the Fish Springs fault,
and perhaps the Owens Valley fault zone as a
whole. Additional study to constrain faulting
rates during the periods between the formation
of the cinder cone, west fan, and north fan
group might be insightful. Dating the offset
lava flows of Crater Mountain would test our
conclusions.
APPENDIX
Field descriptions and laboratory data for soil
profiles are shown in Table A1.
Geological Society of America Bulletin, February 2001
ZEHFUSS et al.
TABLE A1. FIELD DESCRIPTIONS AND LABORATORY DATA FOR SOIL PROFILES
Locality and Nearest Estimated age Horizon
site number sampled
(k.y.)†
boulders
West fan
Soil 1
FSF-AE
FSF-AD
13969
West Fan
Soil 10
FSF-X
133620
West Fan
Soil 11
FSF-AC
161.9628
North fan A
Soil 2
nf A
group 1
13.260.9
North fan A
Soil 3
nfA
group 1
13.260.9
North fan A
Soil 4
FSF-W
FSF-V1
FSF-V2
13.160.4
North Fan A
Soil 5
FSF-C
FSF-B
11.860.6
North Fan A
nfA
Soil 7
group 1
13.260.9
North Fan A
nfA
Soil 9
group 1
13.260.9
South Fan
Soil 6
1.560.6
Tread
Soil 8
FSF-AH#
N.D.
N.D.
A
Av
Bt1
Bt2
Bt3
Cox
A
Bt1
Bt2
Bt3
Cox
A
Bt1
Bt2
Bt3
Bt4
Cox
A1
A2
Bw1
Bw2
Cox
A
Av
Bw1
Bw2
Cox
A
Av
Bw
Cox1
Cox2
A1
A2
Bw1
Bw2
Cox
A1
A2
Bt
Cox
A
Avj
Bw1
Bw2
Btb
A
Bw
2Ab
2Coxb
2Bwb2
2Coxb2
A
Bw1
Bw2
Cox
Bw1b
Bw2b
Depth
(cm)
Munsell color
(dry)
0–4
4–8
8–18
18–53
53–65
65–1291
0–5
5–32
32–49
49–71
71–138
0–7
7–24
24–43
43–58
58–91
91–174
0–4
4–13
13–31
31–58
58–1791
0–4
4–12
12–28
28–64
64–1651
0–4
4–14
14–43
43–58
58–126
0–7
7–14
14–35
35–96
95–1651
0–12
12–53
53–92
92–1421
0–4
4–20
20–38
38–83
83–1171
0–9
9–25
25–53
53–87
87–137
137–1501
0–15
15–47
47–87
87–153
153–183
183–210
10YR 6/3
10YR 6/3
7.5YR 4/4
10YR 5/4
10YR 5/6
2.5Y 5/4
10 YR 5/3
10 YR 6/4
10 YR 5/4
10 YR 6/4
2.5 Y 6/4
10 YR 6/3
10 YR 5/4
10 YR 4/4
10 YR 4/4
10 YR 5/4
2.5 Y 6/4
2.5Y 6/2
2.5Y 6/4
10YR 5/4
2.5Y5/4
10YR 5/6
10 YR 4/3
10 YR 4/3
10 YR 5/6
10 YR 5/6
2.5 Y 5/6
10 YR 5/3
10 YR 6/3
10 YR 6/3
2.5 Y 6/4
2.5 Y 6/2
2.5 Y 6/2
2.5 Y 6/2
10 YR 5/4
10 YR 5/3
2.5 Y 6/4
10 YR 5/3
10 YR 4/3
10 YR 6/4
2.5 Y 5/6
10 YR 5/3
10 YR 5/3
10 YR 6/4
10 YR 5/4
10 YR 5/6
10 YR 5/3
10 YR 5/4
10 YR 4/3
10 YR 5/4
10 YR 5/6
10 YR 6/3
10 YR 6/3
10 YR 5/4
10 YR 5/6
2.5 YR 5/4
10 YR 6/6
10 YR 5/6
Structure
Gravel
(%)
sg
10–25
3 vc sbk
,10
sg; 2 m,c abk
25
2 c sbk
25
2 m,c abk
25
2 m abk
25–50
sg
10–25
2 c sbk
,10
2 vc sbk
10
2 c sbk;abk
10–25
2 c abk
50
sg
10–25
2 c sbk
10–25
2 c sbk
25–50
2 c abk;sbk
50
2 c abk;sbk
50
2 m,c abk
50
sg
10–25
2 c sbk
,10
2 m abk
50
2 m abk
50
2 m abk
50
sg
10–25
2 m,c sbk
,10
2 c sbk
10–25
2 m sbk
25–50
2 c abk
50
sg
10–25
1,2 m sbk
,10
2 c abk
25–50, 50
2 m abk
25–50
2 m,c abk
50
sg
25
1 c sbk
10
2- c sbk
25–50
2 m abk
50
2 m abk
50
sg
10–25
1 m sbk
10–25
2 f sbk
75
2 m abk
75
sg
10–25
2 vc sbk
,10
2 m abk
25–50
3 m,c abk
25–50
2 m,c pl;2 m abk
25
sg;1 m sbk
10–25
2 vc sbk
,10
1 vf sbk
,10
sg
50–75
1,2 m sbk
50
2 m abk
50
sg
10–25
2 c sbk
10
2 c sbk
10–25
2 c abk
25
2 c abk,2 c pr
10–25
3 m,c sbk
10–25
Consistency
Wet
Moist Dry
so,po
ss,ps
s,p
ss,pops
ss,po
so,po
sopo
ssps
ssps
sspsss-pssopo
ssps
ssps
ssps
ss-pssopo
so,N.D.§
soss,po
ss,pops
ss,pops
so,po
sopo
sops
sopo
ssps
sops
sopo
ss-psssps
ss-psssps
sopo
ss-pssspsssps
ssps
sopo
ss-po
ssps
ssps
sopo
ssps
ss-psssps
ssps
sopo
sspo
sopo
sopo
sopo
sspssopo
ss-po
ssps
ss-ps
ssps
ssps
lo
lo
fi
sh
fi
h
fr
eh
fi
vh
fi
h
lo
lo
vfr so
fr
shfr
sh
fr
h
lo
lo
vfr so
vfr sh
vfr
hvfr sh
vfr
h
lo
lo
vfr so
vfr so
fr
so
vfr so
N.D. lo
N.D. sh
N.D. sh
N.D. sh
N.D. sh
N.D. lo
N.D. sh
N.D. sh
N.D. h
N.D. h
N.D. lo
N.D. so
N.D. so
N.D. sh
N.D. h
N.D. lo
N.D. so
N.D. vh
N.D. h
N.D. lo
N.D. so
N.D. sh
N.D. vh
N.D. h
N.D. lo
N.D. sh
N.D. so
N.D. lo
N.D. so
N.D. vh
N.D. lo
N.D. sh
N.D. sh
N.D. sh
N.D. sh
N.D. vh
Texture Clay films ,2mm fraction (%) PDI
LS
SL
SCL
SCL
SL
LS
LS
SL
SL
SL
SL
LS
SCL
SCL
SCL
SL
SL
S
LS
SL
SL
LS
S
LS
LS
SL
LS
S
LS
SL
SL
SL
S
S
LS
LS
LS
S
LS
SL
SL
LS
SL
SL
SL
SL
S
LS
LS
S
LS
LS
LS
SL
SL
SL
SL
SL
nil
nil
2,d,pf
2,d,pf
2,d,pf
nil
nil
nil
nil
nil
nil
nil
nil
2,d,pf
2,d,pf
2,d,pf
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
nil
Silt
(50–2 m)
Clay
(,2 m)
18.52
25.80
12.05
15.46
15.84
10.62
12.18
17.10
15.49
16.43
17.27
11.85
13.94
14.55
14.84
14.88
16.84
8.39
9.42
12.62
12.57
14.45†
5.66
12.46
10.99
12.79
13.1
9.51
16.06
17.50
17.17
17.10
7.79
10.87
8.72
10.55
13.62
5.17
9.90
14.62
16.61
13.02
15.94
14.26
14.28
22.61
8.49
10.84
7.51
7.66
10.15
14.29
9.65
15.43
12.57
14.52
17.36
13.61
7.20
13.31
32.74
20.26
9.68
6.35
4.23
17.49
17.17
15.45
11.83
4.46
26.55
23.52
22.07
18.07
9.54
4.04
4.00
8.44
10.61
8.21†
3.32
5.04
5.40
9.99
8.57
3.40
6.94
10.19
9.32
6.40
1.80
1.64
4.82
8.64
6.84
4.24
6.08
10.22
8.68
5.02
7.39
11.40
11.42
18.93
3.00
5.72
4.98
4.13
5.80
7.25
4.13
11.30
8.92
9.37
11.01
11.62
18
2.9
12
3.3
3.7
3.1
2.2
3.4
3.8
0.0
1.5
4.0
**
*Abbreviations from Soil Survey Staff (1975).
†
Estimates ages are averages and standard deviations of ages from nearest sampled boulders calculated using the production rates of Nishiizumi et al. (1989) assuming
an erosion rate of 0.260.1 cm k.y.–1.
§
N.D.—no data.
#
Youngest boulder was chosen because soil PDI reflects most recent debris flow deposition on south fan.
**PDI not calculated for tread because weathering profile was formed by accumulation of sediment and weathering products acquired from above.
ACKNOWLEDGMENTS
Funding for the isotope analysis was from U.S.
Geological Survey National Earthquake Hazard Reduction Program grant USGS 1434-HQ–97-GR–
03032 to P. Bierman and A. Gillespie. Soils work
was funded by GSA and White Mountain Research
Fund grants to P. Zehfuss. S. Thompson, C. Massey,
G. Rhodes, J. Redwine, D. Sutherland, D. Babb, and
J. Macey provided field assistance. E. Clapp, S.
Neis, and J. Southon helped with cosmogenic analysis. This paper benefited from early reviews by S.
Gran, K. Nichols, K. Jenning, D. Santos, and A.
Noren. Additional reviews by M. Reheis, S. Reneau,
and S. Pezzopane are greatly appreciated. We thank
the residents of Fish Springs, J. Willis and the Gorham family, for allowing us to sample on their properties. Cooperation by the Los Angeles Department
of Water and Power and Bureau of Land Management is acknowledged. M.W. Caffee acknowledges
support from the office of Basic Energy Sciences of
Geological Society of America Bulletin, February 2001
SLIP RATES ON THE FISH SPRINGS FAULT, OWENS VALLEY, CALIFORNIA
Lawrence Livermore National Laboratory, operating under the auspices of the Department of Energy
contract ENG-7405.
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MANUSCRIPT RECEIVED BY THE SOCIETY JUNE 11, 1999
REVISED MANUSCRIPT RECEIVED MARCH 1, 2000
MANUSCRIPT ACCEPTED MARCH 15, 2000
Printed in the USA
Geological Society of America Bulletin, February 2001