U.S. Department of the Interior 

U.S. Geological Survey 

Pamphlet to accompany 

Scientific Investigations Map 3430 

2019 

Stratigraphic and Structural Relations in Trench 

Exposures and Geomorphology at the Big Burn, Lily Lake, 

and Lester Ranch Sites, Bear River Fault Zone, Utah and 

Wyoming 

By Suzanne Hecker, Christopher B. DuRoss, David P. Schwartz, Francesca R. Cinti, Riccardo Civico, 

William R. Lund, Adam I. Hiscock, Michael W. West, Tarka Wilcox, and Alivia R. Stoller 
Cover. Photograph to the north along a west-facing fault scarp 4.5 kilometers south-southeast of the Lester Ranch trench 

site (lat 41.049° N., long 110.798° W.). Formation of the scarp caused blockage of an ephemeral stream that flowed to the 

northeast, resulting in ponding of water against the scarp (center of photograph). The continuation of the stream channel 

above the fault is preserved as a swale that intersects the crest of the scarp. Photograph by David P. Schwartz, July 2012. 
Contents 

Introduction.....................................................................................................................................................1 

Methods...........................................................................................................................................................1 

Site Stratigraphy, Structure, and Geomorphology ...................................................................................1 

Big Burn Trench ....................................................................................................................................1 

Lily Lake South Trench .........................................................................................................................3 

Lester Ranch Trench ............................................................................................................................3 

Earthquake Event Evidence..........................................................................................................................3 

Acknowledgments .........................................................................................................................................5 

References Cited............................................................................................................................................5 

Appendix 1.......................................................................................................................................................7 

Figure 

1. Shaded-relief map of the Bear River Fault Zone in relation to other Quaternary faults and the 

eastern boundary of the Basin and Range physiographic province....................................2 

Table 

1. Location and quality of earthquake event evidence from Big Burn, Lily Lake south, and 

Lester Ranch paleoseismic trenches........................................................................................4 

i 

Introduction 

This report provides trench photomosaics, logs and related 

site information (sheets 1–3), age data (appendix 1), and earthquake event evidence (table 1) from three paleoseismic trench 

sites on the Bear River Fault Zone. Our motivation for studying 

the Bear River Fault Zone—a nascent normal fault in the Rocky 

Mountains east of the Basin and Range physiographic province 

(fig. 1)—is twofold: (1) the intriguing conclusion from previous 

work that the neotectonic history of the fault may have begun 

in the middle to late Holocene and consists of only two surfacerupturing earthquakes (West, 1993, 1994) and (2) the question 

of whether large scarps (>10 meters [m] in height) observed 

along the fault represent net tectonic displacement, which, 

given a two-event history, would put the displacements among 

the largest in the Basin and Range region (Hecker and others, 

2010). In presenting our trench and initial geomorphic interpretations, this report lays the groundwork for further exploration 

of these issues. 

The surface trace of the west-dipping Bear River Fault 

Zone is ~44 kilometers (km) long, extending from the north 

flank of the Uinta Mountains (Utah) to 20 km east-southeast 

of Evanston, Wyoming, and comprises synthetic (down to the 

west) and antithetic scarps across a zone as much as 7.5 km 

wide (fig. 1). Two of our trench sites, Big Burn and Lily Lake, 

are located ~10 km from the south end of the fault on the main 

west-facing scarp and on a large antithetic scarp, respectively 

(fig. 1). The antithetic scarp, obscured by forest canopy, was 

unknown prior to this study. An airborne light detection and 

ranging (lidar) dataset with an average pulse density of 1.24 

pulses per square meter (pulse/m2

) made available to us by 

the U.S. Forest Service allowed more detailed mapping of the 

fault’s south end. The third site, Lester Ranch, is located on a 

prominent west-facing scarp in a section of right-stepping en 

echelon strands, ~11 km from the north end of the mapped fault 

in Wyoming (fig. 1). The southern sites are within glacial terrain 

on deposits mapped by Bryant (2010) as till (at Big Burn) and 

outwash (at Lily Lake) related to the late Pleistocene Pinedale 

glaciation. The Lester Ranch site is located on Pleistocene alluvial deposits that overlie a pediment cut on bedrock consisting 

of the Eocene Wasatch Formation (Dover and M’Gonigle, 1993; 

Reheis, 2005). Big Burn and Lester Ranch were two of several 

sites trenched in the early 1980s and the original Lester Ranch 

trench provided the clearest evidence of a two-event history on 

the fault (West, 1993, 1994). 

Methods 

We excavated paleoseismic trenches across the Bear 

River Fault Zone at the Big Burn site in 2009, Lily Lake 

(antithetic fault) in 2013, and Lester Ranch in 2016. Field 

crews spent 5 to 8 days at each site and our field work followed 

established paleoseismic trenching practice (for example, 

McCalpin, 2009a). The trenches were excavated perpendicular 

to the scarps with rubber-tired backhoes, with vertical south 

wall exposures, and sloped and benched north wall exposures 

for stability. Because of the exceptional size of the scarp at Big 

Burn (~17 m high; sheet 1), we were only able to excavate into 

the base (lower 5 m) of the scarp and across an adjacent closed 

depression. The vertical south wall of each trench was gridded 

at 1-m spacing (2 m horizontal and 1 m vertical spacing at Big 

Burn) using a measuring tape and level. We then photographed 

the wall and created a composite image (photomosaic), which 

was used as a base map to log the exposed stratigraphy and 

structures. For the Big Burn and Lily Lake trenches, we created 

the photomosaics by manually rubber-sheeting photographs 

of each string-gridded rectangle onto a rectangular grid. For 

the Lester Ranch trench, we used structure-from-motion 

photogrammetry with overlapping photographs (>50 percent) 

and with marked grid intersections (but no string) to create a 

seamless, high-resolution photomosaic of the wall (see Reitman 

and others, 2015, for an example of the methodology). We 

sampled detrital charcoal, organic fragments, and (or) sediment 

containing organic material for radiocarbon dating and sampled 

fine to medium sand for optically stimulated luminescence 

(OSL) dating at strategic locations in the trenches to establish 

chronological constraints on the evidence of paleoseismic 

events. 

Site Stratigraphy, Structure, and 

Geomorphology 

Big Burn Trench 

The Big Burn trench, located at the base of the main, westfacing scarp in Utah, exposed tilted and faulted glacial deposits 

overlain by a younger 1.5-m-thick sequence of depression-fill 

deposits and colluvium (sheet 1). The closed depression at the 

base of the scarp was originally thought to be caused by antithetic faulting, but lidar imagery (from data obtained from the 

U.S. Forest Service in 2012) shows that the depression is related 

to the original undulating glacial topography. This observation 

is consistent with the absence of measurable displacement on 

mapped fractures west of the main scarp (sheet 1). 

The infill and colluvial sequence at the base of the scarp 

at the Big Burn site is much thinner than would be expected for 

such a large scarp produced by surface faulting. Although the 

trench did not reach as high as the middle of the scarp where 

the main fault plane would be expected (McCalpin, 2009b), 

scarp degradation models for morphologically simple scarps 

predict that the maximum thickness of colluvium deposited on 

a nearly horizontal surface is approximately 50 percent of the 

scarp height (McCalpin, 2009b), which would mean a colluvial 

thickness of ~8.5 m for the simple (smooth-faced) ~17-m-high 

scarp at the Big Burn trench (sheet 1). A key observation is 

that an illuvial soil horizon (a Btk horizon characterized by 

accumulation of silicate clays and calcium carbonate) mapped 

in the glacial till lies in a slope-parallel orientation beneath the 

lower portion of the scarp (beneath thin hillslope colluvial units 

1ch and 2ch and truncated by scarp colluvial unit 3cs; horizontal meter 2 to 6, sheet 1). We interpret this to indicate that 

1 
MARTIN RANCH FAULT 

COLORADO

110°50' 110°45' 

41°10' 

113° 112° 111° 110° 109° 

IDAHO

42° 

Lester Ranch 

Evanston 

ROCKY 

Great

WYOMING WYOMING Salt 41° 41° 

UTAH Lake BASIN MOUNTAINS 

Area of map 

at right Uinta Mountains 

Salt Lake 

City 

AND 

UTAHBig Burn 

RANGE 

40° 

Lily Lake 

Shaded relief above from Shuttle Radar Topography Mission 3-arc-second digital elevation model; shaded relief at right from U.S. Geological Survey 10-meter digital 0 25 50 MILES 40°50' elevation model 

0 25 50 KILOMETERS 

EXPLANATION 

Bear River Fault Zone—Faults are solid where  accurately located, dotted where inferred Quaternary faults 0 2.5 5 MILES 

Physiographic province boundary 0 5 KILOMETERS Trench sites 

Figure 1. Shaded-relief map of the Bear River Fault Zone in relation to other Quaternary faults and the eastern boundary of the Basin and Range physiographic province. Fault locations are from the Quaternary Fault and Fold Database of the United States (QFFD; U.S. Geological Survey and Utah Geological Survey, 2016). Map inset shows the location of our paleoseismic trench sites on the Bear River Fault Zone. Fault trace is modified from QFFD using light detection and ranging (lidar) shaded-relief imagery in Utah south of ~40°55’30’’ N (from data provided by U.S. Forest Service) and 1994–2017 Google Earth imagery farther north in Utah and Wyoming. The 4-kilometer-long down-to-the-west Martin Ranch Fault is included here as part of the Bear River Fault Zone. 

2 
the ground surface here was tilted forward and bent, or folded, 

rather than being substantially faulted (sheet 1; see discussion 

of monoclinal scarps in McCalpin, 2009b). A monoclinal-folding origin for the scarp, whereby material was not exposed on a 

steep free face, would account for the paucity of colluvium and 

also for the unusually narrow (undegraded) scarp crest and base 

as well as the planar midsection (sheet 1). Folding of the land 

surface also explains the apparent preservation of hummocky 

glacial morphology across the face of the scarp, as identified on 

bare-earth shaded-relief imagery (sheet 1). 

Lily Lake South Trench 

The Lily Lake south trench, located 1 km west of the Big 

Burn site on a large east-facing scarp, also shows evidence for 

monoclinal folding of glacial deposits (sheet 2). This antithetic 

strand of the Bear River Fault Zone cuts across a west-facing 

valley-side hillslope, forming an uphill-facing scarp expressed 

as a prominent bench (sheet 2). We excavated two trenches 

across this bench, the northern of which appeared to be less 

informative, as it exposed a stack of massive mass-wasting 

deposits with poorly expressed faults, and thus was not logged. 

The south trench was sited across a geomorphic low where sediment has collected, forming a small flat. Glaciofluvial deposits 

(unit 3gf) exposed beneath the outer edge of the topographic 

bench are gently folded across the hinge of an east-facing 

monocline (near meter 14, sheet 2). These units are also cut by 

minor down-to-the-east faults (near meter 12). Mass-wasting 

and alluvial deposits (units 2tf, 2tfm, and 2tfa; meter 5 to 13) 

infill the structural trough produced by the monoclinal folding 

and related faulting and are, in turn, tilted eastward on the limb 

of the growing monocline. Ponded sediments infill the depression created by folding of the trough-fill sequence (unit 1df, 

meter 2 to 7), and these deposits have been slightly faulted as 

well. Folding documented in the trench is responsible for most 

(~5.5 m) of the ~6.5 m of vertical separation measured at the 

site (sheet 2). 

Lester Ranch Trench 

In contrast to the sites on glacial deposits, where surface 

displacement is accommodated mainly by folding, the Bear 

River Fault Zone ruptures through to the ground surface at the 

Lester Ranch site, which lies on Eocene Wasatch Formation 

(Tw) bedrock covered by only a thin veneer of deposits (sheet 

3). The main fault zone exposed in the Lester Ranch trench 

consists of several fault strands (F1–F3) in a 6-m-wide zone 

that has accommodated about 6 m of down-to-the-west vertical 

separation of Pleistocene pediment alluvium (4al, sheet 3). 

Bedrock stratigraphy exposed across F1 is not readily correlatable, and the easternmost strand of F2 appears to terminate 

at the base of the Pleistocene alluvium, suggesting an older 

history of faulting. The alluvium and bedrock beneath the 

fault scarp are overlain by elongate, wedge-shaped deposits 

of colluvium (units 2csw, 2csd, and 3cs). Soils or subtle 

weathering zones mark the top of the alluvium and the top of 

the lower colluvium. An apparent debris slide in the upper part 

of the colluvial section (unit 1ds), suspected of being seismically triggered, is evidenced by (1) a thickening of deposits 

that corresponds to the location of an irregular, gently sloping 

topographic bench (meter 16 to 22.5, sheet 3), which extends 

along the base of the scarp for ~80 m, (2) a concave-up contact 

within the deposits (the slide plane), expressed as differential 

relief and a discontinuous light-colored zone partly bleached 

of organics, and (3) a small scarp (near meter 13) and surface 

depression upslope of the slide mass (meter 13 to 14.5) that 

we interpret as the head scarp and upper part of the source 

area. The head scarp is underlain by minor distributed faulting 

and may be tectonic in part. An alternative explanation for the 

bench, supported by its linearity and extent, but controverted 

by its side-sloping morphology, is that it is a bladed road created along the base of the fault scarp. The longstanding ranch 

owner was unaware of any earthmoving activities at that location, however. The bench is visible on 1:20,000-scale aerial 

photographs from 1960 (U.S. Department of Agriculture Farm 

Service Agency, 1960).

Earthquake Event Evidence 

In table 1, we present evidence of ground-deforming 

earthquakes observed in the trenches (sheets 1–3) and we 

evaluate the quality of each piece of evidence, similar to the 

ranking system developed by Scharer and others (2007) for 

strike-slip faults. We use a three-tiered scale of low, moderate, 

and high to reflect the degree of certainty that the observed or 

inferred deformation was produced by an earthquake.

We find evidence consistent with a record of three 

earthquakes at each site, although the strength and number 

of observations vary between events and trenches (table 1). 

Evidence for three earthquake events is strong at Lily Lake, 

whereas evidence for the youngest event (E1) is fairly weak 

at both Big Burn and Lester Ranch. Inspection of the available radiocarbon and OSL ages (sheets 1–3; appendix 1) and 

comparison of the Lester Ranch trench log (sheet 3) with the 

log from the 1983 trench exposure indicate that the two older 

earthquake events (E2 and E3) likely correspond to the middle 

to late Holocene ruptures identified by West (1993, 1994). The 

youngest event (E1), which was not recognized prior to our 

study, likely occurred within the last several hundred years, as 

indicated by ages of macrofloral remains from deposits that 

predate the earthquake (table 1.2). 

Elements of this study yet to be completed include 

(1) documenting off-fault evidence for E1, (2) analyzing 

earthquake event ages, (3) estimating cumulative and event 

displacements on the fault, and (4) considering the factors 

responsible for clustering of large earthquakes on the Bear 

River Fault Zone and perhaps on other faults in comparable 

settings (Hecker and Schwartz, 2018).

3 
4 

Table 1. Location and quality of earthquake event evidence from Big Burn (BB), Lily Lake south (LL), and Lester Ranch (LR) 

paleoseismic trenches (sheets 1, 2, and 3, respectively), Bear River Fault Zone, Utah and Wyoming. 

Trench–Event Event evidence Quality 

rank Description and interpretation of event evidence 

BB–E3 Base of depression-fill Moderate Initiation of sedimentation in closed basin adjacent to scarp 

deposits (unit 3df, meter 7 likely triggered by initial post-glacial deformation 

to ~18?) 

BB–E3 Scarp colluvium (unit 3cs, Moderate Wedge-shaped deposit truncates the Btk soil horizon developed 

meter 6 to 8) in glacial deposits and grades laterally into depression fill; 

original geometry of wedge and associated scarp is somewhat 

ambiguous 

BB–E3 Upward fault terminations Low Terminations at base of units 3df and 3cs may be apparent only; 

(meter 6 to 7) material properties allow for concealment of minor faults

BB–E2 Hillslope colluvium (unit Moderate Discrete coarse-grained slope deposit buries older colluvium 

2ch, meter 2 to 9) (unit 3cs) and extends farther downslope, suggesting a shift 

in the toe of the slope owing to growth of the scarp; sediment 

mobilization inferred to be triggered by folding event (blind 

causative fault) that steepened and broadened the flexure and 

possibly by minor fault rupture higher on the scarp (though 

not evidenced in the scarp’s morphology) 

BB–E2 Top of depression infill (unit Low Slope colluvium is buried by continued or renewed ponding 

3df) that buries toe of unit of sediment in the depression, consistent with deformation2ch colluvium (meter 9) induced sedimentation 

BB–E1 Hillslope colluvium (unit Low Discrete, but thin, slope deposit that buries older colluvium 

1ch, meter 2 to 10) (unit 2ch) and extends farther downslope, suggesting a shift 

in the toe of the slope owing to growth of the scarp; sediment 

mobilization inferred to be triggered by folding event (blind 

causative fault) that steepened and broadened the flexure; 

however, matrix-supported nature of deposit allows for an 

alternative sediment-mobilization mechanism (for example, a 

storm event) 

LL–E3 Unconformable relation High Alluvial and mass-wasting deposits accumulated in a broad 

between top of folded hillside trough (uphill-facing scarp) created by folding and 

glacial deposits (unit 3gf) eastward tilting of glacial deposits that underlie the hillside

and overlying trough-fill 

deposits (units 2tf, 2tfm 

and 2tfa, meter 10 to 16)

LL–E2 Unconformable relation be- High Predominately fine-grained sediments accumulated in depression 

tween top of folded trough- created by folding and eastward tilting of trough-fill sequence 

fill deposits (unit 2tfm) and (rejuvenating the buried uphill-facing fold scarp); depressionoverlying depression-fill fill unit thickens over fold hinge and pinches out against fold 

deposits (unit 1df, meter limb 

2 to 7)

LL–E1 Faulting of post-E2 depres- High Displacement of unit 1df and overlying top soil forms a small 

sion-fill deposit (unit 1df) (~15-centimeter-high) scarp on the forest floor

and ground surface (meter 

5 to 6)

LR–E3 Scarp colluvium (unit 3cs, Moderate Faulted and truncated colluvial deposit that buries what appears 

meter 14 to ~19) to be the pre-faulting ground surface (deposit interpreted to 

be unit 4al, with remnant soil horizon, between faults F2 and 

F3), recording the first scarp-forming event; deposit thickens 

in small graben at meter 15

LR–E3 Upward termination of fault Moderate F3 appears to thrust a block of unit 4al onto the event ground 

F3 (meter 17 to 17.5) surface (top of A horizon formed in unit 4al); however, position of ground surface is uncertain and properties of overlying 

material (unit 3cs) allow for upward continuation of minor 

faulting 
Table 1. Location and quality of earthquake event evidence from Big Burn (BB), Lily Lake south (LL), and Lester Ranch (LR) 

paleoseismic trenches (sheets 1, 2, and 3, respectively), Bear River Fault Zone, Utah and Wyoming.—Continued. 

Trench–Event Event evidence Quality 

rank Description and interpretation of event evidence 

LR–E2 Scarp colluvium (units 2csw High Lower coarser grained facies (unit 2csd, meter 14 to 18) is disand 2csd, meter 9.5 to tinct from underlying unit 3cs colluvium (and separated from 

~19) it by a subtle soil) and contains blocks of material suspected 

to be derived from an upthrown unpreserved portion of unit 

3cs east of F2; the upper deposit (unit 2csw), interpreted as 

mainly wash-facies colluvium (with coarser grained deposits 

upslope from F1 at meter 11), is unusually laterally extensive 

and its genesis is not entirely clear 

LR–E1 Fractures mapped in E2 col- Low Distributed fractures and minor faults appear to extend to, or 

luvium (meter 10 to 16); close to, the ground surface; unfilled voids along fractures in 

open fractures in unit 4al unit 4al suggest recency of faulting 

(meter 3 and 7)

LR–E1 Debris slide off of scarp (me- Low Spatial association with fault zone suggests apparent slope 

ter 13 to 22.5) failure was triggered by ground shaking and possibly surface 

rupture; however, an artificial origin for the topographic bench 

formed by the deposit (unit 1ds) cannot be precluded 

Acknowledgments 

This work was funded by internal funds of the Earthquake 

Hazard Reduction Program of the U.S. Geological Survey; 

fieldwork at the Big Burn and Lily Lake sites was materially 

supported by the Utah Geological Survey. We thank the U.S. 

Forest Service for providing an airborne lidar dataset that was 

collected within the Uinta-Wasatch-Cache National Forest in 

September 2010, and we thank Ellen Phillips and Luke Blaire 

for creating the lidar-derived digital elevation model. We are 

grateful to Bernard Asay, Evanston-Mountain View Ranger 

District, for his assistance obtaining access to sites in the 

National Forest and to Craig Lester for his willingness to let us 

trench on his land. Thanks to Joey Mason for initial digitization 

of the Lester Ranch trench log. Scott Bennett and Rich Briggs 

provided thorough and thoughtful reviews of an earlier draft of 

the manuscript. 

References Cited 

Bryant, B., 2010, Geologic map of the east half of the Salt Lake 

City 1° x 2° quadrangle (Duchesne and Kings Peak 30ʹ×60ʹ

quadrangles), Duchesne, Summit, and Wasatch Counties, 

Utah, and Uinta County, Wyoming (digitized and modified 

from U.S. Geological Survey Miscellaneous Investigations 

Series Map I-1997, published in 1992): Utah Geological Survey Miscellaneous Publication 10-1DM, GIS data, 2 plates, 

scale 1:125,000.

Dover, J.H., and M’Gonigle, J.W., 1993, Geologic map of the 

Evanston 30ʹ×60ʹ quadrangle, Uinta and Sweetwater Counties, Wyoming: U.S. Geological Survey Miscellaneous 

Investigations Series Map I-2168, scale 1:100,000.

Hecker, S., Dawson, T.E., and Schwartz, D.P., 2010, Normal-faulting slip maxima and stress-drop variability—A

geological perspective: Bulletin of the Seismological 

Society of America, v. 100, no. 6, p. 3130–3147, https://

dx.doi.org/10.1785/0120090356. 

Hecker, S., and Schwartz, D.P., 2018, Behavior of a new 

normal fault in the Rocky Mountains—Implications for 

continental intraplate earthquakes [abs.]: Geological 

Society of America Abstracts with Programs, v. 50, no. 6, 

https://doi.org/10.1130/abs/2018AM-324944. 

McCalpin, J.P., 2009a, Field techniques in paleoseismology—Terrestrial environments, chap. 2A of McCalpin, 

J.P., ed., Paleoseismology (2d ed.): International Geophysical Series, v. 95, p. 29–118.

McCalpin, J.P., 2009b, Paleoseismology in extensional 

tectonic environments, chap. 3 of McCalpin, J.P., ed., 

Paleoseismology (2d ed.): International Geophysical 

Series, v. 95, p. 171–269.

Prescott, J.R., and Hutton, J.T., 1994, Cosmic ray contributions to dose-rates for luminescence and ESR dating—

Large depths and long-term time variations: Radiation 

Measurements, v. 23, no. 2/3, p. 497–500.

Reheis, M.C., 2005, Surficial geologic map of the upper 

Bear River and Bear Lake drainage basins, Idaho, Utah, 

and Wyoming: U.S. Geological Survey Scientific Investigations Map 2890, scale 1:50,000 and 1:150,000.

Reitman, N.G., Bennett, S.E.K., Gold, R.D., Briggs, R.W., 

and DuRoss, C.B., 2015, High-resolution trench photomosaics from image-based modeling—Workflow and 

error analysis: Bulletin of the Seismological Society of 

America, v. 105, no. 5, p. 2354–2366. 

5
6

Scharer, K.M., Weldon, R.J., Fumal, T.E., and Biasi, G.P., 

2007, Paleoearthquakes on the southern San Andreas Fault, 

Wrightwood, California, 3,000 to 1,500 B.C.—A new 

method for evaluating paleoseismic evidence and earthquake 

horizons: Bulletin of the Seismological Society of America, 

v. 97, p. 1054–1093, https://dx.doi.org/10.1785/0120060137. 

Stuiver, M., and Pollach, H.A., 1977, Discussion—Reporting 

of 14C data: Radiocarbon, v. 19, p. 355–363.

Stuiver, M., Reimer, P.J., and Reimer, R.W., 2017, CALIB 7.1 

[WWW program] accessed May 3, 2017, at http://calib.org. 

U.S. Department of Agriculture Farm Service Agency, 1960, 

Aerial photographs flown August 18, 1960: U.S. Department 

of Agriculture Aerial Photography Field Office photographs 

CVT-6AA-122 and 123, scale 1:20,000 [vertical black and 

white film].

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2016, Quaternary fault and fold database for the United 

States: U.S. Geological Survey database, accessed 

October 6, 2016, at https://earthquake.usgs.gov/hazards/

qfaults/. 

West, M.W., 1993, Extensional reactivation of thrust faults 

accompanied by coseismic surface rupture, southwestern Wyoming and north-central Utah: Geological Society of America Bulletin, v. 105, p. 1137–1150.

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and southwestern Wyoming in Paleoseismology of Utah, 

v. 4: Utah Geological Survey Special Study 82, 93 p. 

6
Appendix 1 

Table 1.1 Results of radiocarbon age dating of detrital charcoal from Big Burn (Bear) and Lily Lake south 

(LLS) trenches, Bear River Fault Zone, Utah; data collected at the Center for Accelerator Mass Spectrometry, 

Lawrence Livermore National Laboratory. 

[‰, parts per thousand; yr B.P, years before present; cal. yr B.P., calibrated years before present]

Lab number 

(CAMS no.)a Field numberb Report date d13C (‰)c

14C age 

(yr B.P.)d

Calibrated age 

(cal. yr B.P.)e

146537 Bear 4 (R-B4) Mar. 14, 2010 −25 4,330 ± 35 4,970–4,840

146538 Bear 6 (R-B6) Mar. 14, 2010 −25 2,495 ± 30 2,730–2,470

166517 LLS-S1* June 23, 2014 −23.02 675 ± 30 680–560

166518 LLS-S2* June 23, 2014 −24.04 860 ± 30 900–690

166519 LLS-S3* June 23, 2014 −26.87 3,710 ± 30 4,150–3,980

166520 LLS-S4* June 23, 2014 −25.01 3,095 ± 25 3,370–3,240

166521 LLS-S5* June 23, 2014 −21.96 3,020 ± 30 3,320–3,080

166528 LLS-S6* June 23, 2014 −25.2 905 ± 25 910–760

166522 LLS-S7* June 23, 2014 −24.09 3,050 ± 30 3,350–3,180

a

 Laboratory identifier: CAMS, Center for Accelerator Mass Spectometry, Lawrence Livermore National Laboratory.

b

 Samples with an asterisk (*) were large enough for d13C aliquots to be taken. 

c d13C values are the assumed values according to Stuiver and Polach (1977) when given without decimal places. Values measured 

for the material itself are given with decimal places. 

d

 Reported in radiocarbon years before present (1950) using the Libby half-life of 5,568 years and following the conventions of 

Stuiver and Polach (1977). Error is one standard deviation (1σ) analytical uncertainty.

e

 2σ calibrated age range rounded to nearest decade; calibration from CALIB 7.1 program (Stuiver and others, 2017). 

Table 1.2 Results of radiocarbon dating of macrofloral remains from Lily Lake south (LLS) and Lester Ranch (LR) trenches, 

Bear River Fault Zone, Utah and Wyoming; data collected at the PaleoResearch Institute in Golden, Colorado. 

[‰, parts per thousand; %, percent; AMS, accelerator mass spectrometry; yr B.P., years before present; cal. yr B.P., calibrated years before present]

Sample number Sample identification Report date d13C (‰)a AMS 14C age 

(yr B.P.)b 

Calibrated age 

(cal. yr B.P.)c 

PRI-14-071-LLS9-1 Pinus cone scale, charred January 2015 −23.6 244 ± 22 310–280 (73)

170–150 (25)

PRI-14-071-LLS9-2 Pinus cone scale, charred January 2015 −24.3 369 ± 21 500–430 (63)

380–320 (36)

PRI-14-071-LLS9-3 Pinus needle, charred January 2015 −25.7 387 ± 23 510–430 (79)

360–330 (20)

PRI-5610-LR-1 Artemisia and unidentified 

hardwood charcoal, incompletely charred 

February 2017 −26.16 378 ± 22 500–430 (71)

380–320 (29)

a d13C values are measured by AMS during the 14C measurement. The AMS d13C values are used for the 14C calculation and should not be used for 

dietary or paleoenvironmental interpretations. 

b

 Reported in radiocarbon years before present (1950) with one standard deviation (1σ) analytical uncertainty, corrected for d13C. 

c

 2σ calibrated age range rounded to nearest decade; calibration from CALIB 7.1 program (Stuiver and others, 2017). Parenthetical probabilities of 

occurrence, in percent, reflect multimodal age distributions. 

7
Table 1.3 Quartz optically stimulated luminescence (OSL) data and ages for Lily Lake south and Big Burn trenches, Bear River Fault Zone, Utah, from the U.S. 

Geological Survey Luminescence Dating Laboratory in Denver, Colorado. 

[%, percent; wt. %, weight percent; ppm, parts per million; Gy, grays; Gy/ka, grays per thousand years]

8 

Water Cosmic dose Total dose rate Equivalent Scatter nd Field number K (wt. %)b U (ppm)b Th (ppm)b Age (years)f content (%)a (Gy/ka)c (Gy/ka) dose (Gy) (%)e

OSL-LLS1 1 (24) 2.30 ± 0.04 2.23 ± 0.20 13.3 ± 0.37 0.30 ± 0.01 3.82 ± 0.08 60.8 ± 3.83 3 (30) 43 15,910 ± 1,060

OSL-B1 0 (31) 2.55 ± 0.10 2.79 ± 0.26 12.5 ± 0.54 0.28 ± 0.01 4.05 ± 0.11 18.2 ± 0.52 9 (20) 41 4,500 ± 280

OSL-B2 0 (23) 2.37 ± 0.07 3.05 ± 0.22 11.3 ± 0.48 0.28 ± 0.01 3.94 ± 0.10 13.5 ± 0.44 7 (18) 43 3,430 ± 200

OSL-B3 0 (21) 2.77 ± 0.05 2.15 ± 0.19 11.3 ± 0.42 0.29 ± 0.01 4.13 ± 0.09 55.0 ± 1.68 8 (18) 31 13,310 ± 500

OSL-B4 0 (27) 2.02 ± 0.04 2.34 ± 0.17 10.8 ± 0.46 0.30 ± 0.01 3.40 ± 0.08 31.9 ± 0.78 14 (20) 39 9,390 ± 360

Ages calculated using field moisture.

 Number of replicated equivalent dose estimates used to calculate the equivalent dose. Figures in parentheses indicate total number of measurements included in calculating the represented 

e poorly bleached (or mixed) Values >25 percent are considered to b

ent doses; reported errors are two standard deviations, ages and errors rounded to nearest decade.

 Field moisture; figures in parentheses indicate the complete sample saturation percentage. 

Analyses obtained using high-resolution gamma spectrometry (Ge detector).

 Cosmic doses and attenuation with depth were calculated using the methods of Prescott and Hutton (1994).

equivalent dose and age using the minimum age model. 

 Defined as “over-dispersion” of the equivalent dose values; obtained by dividing the average by the standard deviation. 

sediments. 

b 

Age for fine-grained (180–250 microns) quartz. Exponential fit used on equival

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