?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

?

OSL-B4

9,390 ± 360 yr

OSL-B3

13,310 ± 500 yr

OSL-B1

4,500 ± 280 yr

OSL-B2

3,430 ± 200 yr

R-B4

4,970–4,840 cal. yr B.P.

R-B6

2,730–2,470 cal. yr B.P.

B2

B3

B5

B1

4gt

1ch

1ch

2ch 

2ch

3df

3df

3df

4gt

4gf

4gt

4gt 4gt

4gt

4gt 4gt

4gt

4gt

4gt

3df

3cs

4gf

2ch

1ch

4gt

4gt

4

6

4

6

8

10

8

10

12

14

12

14

16 18

16 18

20

22

24

26

24

20

22

26

28

30

32

34

1

2

3 3

4 4

5

6

5

6

EAST

WEST

4

3

4

3

2

1

7 7

34

32

30

28

2

2

Photograph of the view along the Big 

Burn trench toward the fold scarp. 

Dashed white line marks the base of 

the scarp; evergreen trees grow 

along the scarp crest.

Lidar shaded relief displayed in Google Earth © 2017 showing perspective 

view looking southward along the main, west-facing fold scarp in Utah, 

with southeast illumination and similar coverage to the image at left (scale 

bar represents foreground). The red balloon marks the Big Burn trench 

site. The broad, uniform-sloping face of the scarp (in shadow) is formed by 

the limb of the presumed monocline; the narrow crest and base reflect 

sharp fold hinges (see also scarp profiles at right). This morphology 

contrasts with that expected for a degraded normal-fault scarp, which 

should develop a rounded base as colluvium accumulates below the 

vertical free face (for example, McCalpin, 2009b). A folding origin for the 

scarp is evidenced also by along-strike undulations of the scarp face (seen 

as subtle gray-tone variations on the lidar image), some of which can be 

traced onto the geomorphic surfaces above and below the scarp (example 

at trench site indicated by arrows) and express the hummocky morphology 

of the pre-folding glaciated landscape. 

0 25 50 75 100 METERS

0 50 100 150 200 250 300 FEET

N

Base from 0.25-meter digital elevation model created 

from data provided by the U.S. Forest Service

4

EXPLANATION OF TRENCH SYMBOLS

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

queried where uncertain

Soil horizon boundary

Base of A horizon developed in underlying unit—Queried where uncertain

Top of buried A horizon

Top of Btk (illuvial) horizon developed in glacial till—Soil matrix properties: 

loamy sand; 5YR 4/3 dry, 3/3 moist (Munsell color); nonplastic; slightly hard 

to hard dry consistence; weak subangular blocky structure; common faint 

clay films bridging sand grains; <1-millimeter-thick zones of bleaching along 

fractures; weak (stage I) carbonate morphology. Queried where uncertain

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)

Radiocarbon-dated charcoal sample with calibrated age—Sample number 

and age shown

Undated charcoal sample—Sample number shown

Sediment sample with optically stimulated luminescence (OSL) 

age—Sample number and age shown

String grid placed during trenching

Grid-node tag placed during trenching

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

reference frame). Horizontal interval is 2 meters; vertical interval is 1 meter

DESCRIPTION OF TRENCH UNITS

Hillslope colluvium (earthquake event 1 evidence?)—Unstratified, mostly 

matrix-supported, bimodally sorted gravelly loam

Hillslope colluvium (earthquake event 2 evidence)—Unstratified, 

clast-supported, bimodally sorted very gravelly loam

Depression-fill deposits (earthquake events 2 and 3 evidence)—Poorly 

stratified silty clay loam with scattered gravel; becomes more gravelly near 

scarp colluvium (3cs) at meter 7–10

Scarp colluvium (earthquake event 3 evidence)—Poorly stratified, mostly 

matrix-supported, poorly sorted gravelly loamy sand; grades laterally into 

depression-fill deposits (3df)

Glacial deposits

Glacial till (late Pleistocene Pinedale glaciation)—Unstratified to poorly 

stratified, mostly matrix-supported and poorly sorted, gravelly to very 

gravelly loamy sand

Glaciofluvial deposits (late Pleistocene Pinedale glaciation)—Moderately 

well-stratified loamy sand

4gt

4gf

1ch

2ch

3df

3cs

1

U.S. Geological Survey

2

Utah Geological Survey

3

Istituto Nazionale di Geofisica e Vulcanologia

4

Michael W. West and Associates, Inc.

Big Burn Trench—South Wall Photomosaic and Site Geomorphology, Bear River Fault Zone, Utah

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 

U.S. Department of the Interior

U.S. Geological Survey Scientific Investigations Map 3430

Sheet 1 of 3

Pamphlet accompanies map

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

Light detection and ranging (lidar) shaded-relief orthoimage 

(with southeast illumination; south is to the top) showing 

location of the Big Burn trench (lat 40°52.970' N., 

long 110°48.031' W.) on the main, west-facing fold scarp in 

Utah. The original Big Burn trench (West, 1994) was located 

just to the north of the 2009 trench. Contours emphasize 

scarp and hummocky glacial terrain. Lines mark locations 

of profiles A–A' and B–B' that are shown to the far right. 

See figure 1 of the pamphlet for regional context. 

Big Burn trench

2670

2660

2650

2640

2660

2670

2670

2680

2680

2690

2690

2680

2650

2660

N

CONTOUR INTERVAL 2 METERS

0 30 60 90 120 METERS

0 100 200 300 FEET

Base from 0.25-meter digital elevation model created 

from data provided by the U.S. Forest Service

110°48'

40°53'

110°48'10"

40°52'50"

A

A'

B

B'

Topographic profile B–B' shows a simple profile 

30 m south of Big Burn trench, where vertical 

separation of the ground surface is ~13 m. The 

location of profile B–B' is shown on the lidar 

map at far left. 

~13 m

B B'

EAST WEST

Ground surface

Elevation, in meters (m)

NO VERTICAL EXAGGERATION

2,666

2,662

2,658

2,654

2,670

2,650

2,666

2,662

2,658

2,654

2,670

2,650

0 4 8 12 16 20 24 28 32 36 40 44

0 4 8 12 16 20 24 28 32 36 40 44

Distance, in meters (m)

Topographic profile A–A' (extracted from 0.25-meter digital elevation model) illustrates the position of the soil Btk horizon developed in glacial till, as observed on the trench wall (solid yellow line) and inferred beyond the trench (yellow dashed line). 

Other undulations in the landscape, including the depression at the base of the scarp and the east-facing slope at meter 18–34, are related to pre-existing glacial topography (evident on lidar shaded relief at left) and may contribute to the height of 

the scarp here. The location of profile A–A' is shown on the lidar map at far left. 

2,670

2,674

2,666

2,662

2,658

2,654

2,650

Trench outline

Fold scarp

A A'

EAST WEST

Ground surface

Elevation, in meters (m)

2,646

2,670

2,674

2,666

2,662

2,658

2,654

2,650

2,646

NO VERTICAL EXAGGERATION

EXPLANATION

Top of soil Btk horizon, observed

Top of soil Btk horizon, inferred

Fault

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96 100

Distance, in meters (m)