U.S. Department of the Interior

U.S. Geological Survey

 

Scientific Investigations Map 3430

Sheet 3 of 3

Pamphlet accompanies map

1

U.S. Geological Survey

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Utah Geological Survey

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Istituto Nazionale di Geofisica e Vulcanologia

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Michael W. West and Associates, Inc.

Lester Ranch Trench—South Wall Photomosaic and Site Geomorphology, Bear River Fault Zone, Wyoming

By 

Suzanne Hecker,1 Christopher B. DuRoss,2 David P. Schwartz,1 Francesca R. Cinti,3 Riccardo Civico,3 William R. Lund,2

Adam I. Hiscock,2 Michael W. West,4 Tarka Wilcox,4 and Alivia R. Stoller1

2019 

Editing and cartographic design by Monica Erdman

Manuscript approved for publication March 8, 2019

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not 

imply endorsement by the U.S. Government.

This map or plate is offered as an online-only, digital publication. Users should be aware that, because of 

differences in rendering processes and pixel resolution, some slight distortion of scale may occur when 

viewing it on a computer screen or when printing it on an electronic plotter, even when it is viewed or 

printed at its intended publication scale.

Digital files available at https://doi.org/10.3133/sim3430

Suggested citation: Hecker, S., DuRoss, C.B., Schwartz, D.P., Cinti, F.R., Civico, R., Lund, W.R., Hiscock, A.I., 

West, M.W., Wilcox, T., and Stoller, A.R., 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: U.S. Geological Survey Scientific Investigations Map 3430, 8 p., 3 sheets, 

https://doi.org/10.3133/sim3430.

ISSN 2329-132X (online)

https://doi.org/10.3133/sim3430

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F1

F3

F2

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2csw

2csw

2csw

2csd

2csd

2csd

4al

4al

4al

4al 4al

Tw

4al

3cs

3cs

3cs

3cs

4al

2csw

2csw

2csd

1ds

1ds

1ds

2csd

3cs

4al

4alb

4al

4alb

2/3bd

4al

Tw

Tw

4alb

2csw

Tw

Tw Tw

Tw

Tw

Tw

Tw

Tw

Tw

Tw

Tw

Tw

4alb

4alb 4alb

4alb

4alb

4al

4al

4al

4al

4alb

4alb

4alb

4alb

2/3bd

2/3bd

4al

4al

R-LR-1

500–430 cal. yr B.P. (71%)

380–320 cal. yr B.P. (29%)

openings

open fracture

adjacent to

fault

1

7

6

1

7

6

5

5

4

4

3

3

2

2

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

9

9

10

10

11

11

12

12

13

13

14

14

15

15

16

16

17

17

18

18

19

19

20

20

21

21

22

22

23

23

24

24

25

25

0

0

-1

-1

EAST

WEST

EXPLANATION OF TRENCH SYMBOLS

Krotovina—Queried where uncertain

Colluvial block containing organic matter

Contact—Solid where accurately located, dashed where approximately located, 

queried where uncertain

Soil horizon boundary

Base of A horizon developed in Pleistocene alluvium (4al)—Queried where 

uncertain

Top of buried A horizon

Base of buried weathering zone (bleached A horizon?)—Developed in the 

scarp colluvium (3cs) and Pleistocene alluvium (4al) between faults 

F2 and F3

Base of reddened (B?) horizon—Developed in Pleistocene alluvium (4al) on 

downthrown side of fault F3; sharpness of contact with carbonate-rich zone 

and lack of pedogenic structure may be an effect of shallow ground water

Slide plane—Solid where accurately located, dashed where approximately 

located, queried where uncertain. Arrow indicates direction of movement of 

the sliding unit (1ds)

Light-colored zone along slide plane

Fault

Fault with significant displacement—Numbered sequentially from east to 

west. Arrows indicate direction of relative movement. Solid where accurately 

located, dashed where approximately located

Fracture or minor fault—Solid where accurately located, dashed where 

approximately located, queried where uncertain

Dated sample—All ages are 2-sigma ranges rounded to nearest decade; 

radiocarbon calibration from Stuiver and others (2017). Probabilities are 

shown for multimodal radiocarbon age ranges

Radiocarbon-dated charcoal fragments with calibrated age—Fragments 

combined from bulk sample. Sample number and age shown

Grid-node tag placed during trenching

Trench grid—Horizontal and vertical distances denoted in meters (arbitrary 

reference frame). Interval is 1 meter

DESCRIPTION OF TRENCH UNITS

Debris-slide deposit (earthquake event 1 evidence?)—Semi-coherent mass of scarp 

colluvium (2csw) moved downslope from concave head scarp at meter 12.75

Scarp colluvium, mainly wash facies (earthquake event 2 evidence)—Poorly 

stratified and moderately sorted silty clay loam with coarse sand; locally gravelly. 

Grades laterally into basin deposits (2/3bd) at meter 18–19

Scarp colluvium, debris facies (earthquake event 2 evidence)—Unstratified, 

matrix-supported and poorly sorted gravelly silt loam with coarse sand; uneven 

distribution of carbonate (detrital origin); contains darker blocks, possibly derived 

from the A horizon of a since-eroded soil developed in the upthrown block east of 

fault zone F2

Scarp colluvium (earthquake event 3 evidence)—Poorly stratified silty clay loam, 

gravelly along base and at east end (meter 14–15); uneven distribution of 

carbonate (detrital origin); grades laterally into basin deposits (2/3bd) at meter 

17–19

Basin deposits—Poorly stratified silty clay loam. Grades laterally into scarp 

colluvium (2csw, 3cs) at meter 17–19

Alluvium (Pleistocene)—Deposited on erosional surface cut on underlying bedrock; 

poorly stratified, mostly clast-supported, poorly to moderately sorted, very to 

extremely gravelly loamy medium to coarse sand, slightly indurated moderate 

(stage II+) carbonate morphology

Basal facies—Base of alluvium, where it is less gravelly and less carbonate rich 

than rest of unit (weak stage 1 carbonate morphology); siltier texture at meter 6–9 

and meter 11.5–13.5, possibly reflecting incorporation of eroded unit Tw, also 

extensively bioturbated; visible inclusions of Tw at meter 2–3 and 12.5–13.5

Wasatch Formation (Eocene)—Variegated (yellow, tan, red, and orange) very 

fine-grained sandstone, siltstone, and claystone with local gravelly lenses; 

generally friable, locally indurated; extensively fractured at meter 12.5–13.5

1ds

2csd

2csw

3cs

2/3bd

4al

4alb

Tw

4

W1

W2

Tw

Photograph of a pair of stacked colluvial 

wedges (W1 and W2 of West, 1993 and 

1994) exposed in original 1983 Lester Ranch 

trench, located about 30 meters north of 

the 2016 trench. A vertical-to-overturned 

normal fault juxtaposes colluvium against 

Wasatch Formation (Tw) bedrock. Red 

arrows bracket apparent shears (marked 

with pink nails) that cut the upper colluvial 

wedge (correlative with colluvial debris 

unit 2csd in 2016 trench) and represent 

possible evidence of the third, younger 

faulting event identified in our study. The 

thick, organic-rich deposit at the toe of the 

slope may be correlative with the debrisslide deposit (1ds) in the 2016 trench. Red 

flags on string are 1 meter apart. 

Photograph of a camera 

mounted on a Helikite, a 

tethered helium-kite 

balloon.

Debris-slide 

deposit

(low bench)

Exploratory

pit

2016 trench

Spoils pile

1983 trench erosional 

scar and mobilized 

backfill

41°05'20" 41°05'20"

41°05'25" 41°05'25"

110°47'05"

110°47'05"

110°47'10"

110°47'10"

2016 trench

Spoils pile

Debris slide 

head scarp

Exploratory

pit

1983 trench erosional 

scar and mobilized 

backfill

GPS point

Elevation, in meters (m)

2,310

2,297

EXPLANATION

0 10 20 30 40 METERS

0 25 50 75 100 FEET

N

Orthophotomosaic (left) and digital surface model (DSM, 0.25-m resolution; right) of the Lester Ranch 

trench site created using structure-from-motion (SfM) photogrammetry and balloon-based imagery. 

Yellow dots on orthophotomosaic along the south side of the 2016 trench are global positioning 

system (GPS) points used to obtain a profile of the scarp (shown at lower left).

Perspective view of the Lester Ranch trench site illustrating the method of collecting photographs from a 

balloon-mounted camera for use in structure-from-motion photogrammetry. From changes in camera position 

(T1–T3) and matching of ground features in overlapping photographs (yellow and red dots) depth is calculated. 

Lines of site are represented by the black lines. From the depth data, a shaded relief is created—plotted here 

using Google Earth © 2016.

0 10 20 30 40 METERS

0 25 50 75 100 FEET

T1

T2 T3

N

Photograph of scarp 

at 2016 Lester Ranch 

trench site before 

trenching began.

0 10 20 30 40 50

0 10 20 30 40 50

2,310

2,309

2,308

2,307

2,306

2,305

2,304

2,303

2,302

2,301

2,310

2,309

2,308

2,307

2,306

2,305

2,304

2,303

2,302

2,301

~6 m

Distance, in meters (m)

Elevation, in meters (m)

EAST WEST

VERTICAL EXAGGERATION ×2

Profile of scarp along the south side of the Lester Ranch trench. Yellow dots show GPS points; see orthophotomosaic to right for locations. 

Vertical separation of the ground surface here is ~6 m. Note south-looking perspective. 

Tw

Tw

Tw

4al

4al

4al

4al

4al

4al

csu

csu

csu

EAST WEST

Meters

Meters

0 5 10 15 20 25

7

5

3

1

7

5

3

1

6

4

2

2

4

6

-1 1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 24

-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Simplfied log of the south wall of Lester Ranch trench colored to differentiate scarp-related deposits (csu) from Pleistocene alluvium (4al) and bedrock (Tw).

Tw

csu

4al

Scarp colluvium, undifferentiated—Includes 

 material remobilized in debris slide

Alluvium (Pleistocene)

Wasatch Formation (Eocene)

Contact—Solid where accurately located, 

 dashed where approximately located

Base of soil A horizon

Fault—Solid where accurately located, 

 dashed where approximately located

Slide plane—Solid where accurately located, 

 dashed where approximately located. 

 Arrows indicate direction of movement

 of slide mass

Internal contact—Accurately located

Internal contact—Approximately located

EXPLANATION