Logs and Data from Trenches Across and Near the Green 

Valley Fault at the Mason Road Site, Fairfield, Solano 

County, California, 2006–2009

By James J. Lienkaemper, Robert R. Sickler, Shannon A. Mahan, Johnathan Brown, Liam M. Reidy, 

and Mindy A. Kimball 

Pamphlet to accompany 

Open-File Report 2012–1011

2012

U.S. Department of the Interior

U.S. Geological Survey 
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS—the Federal source for science about the Earth, 

its natural and living resources, natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Suggested citation:

Lienkaemper, J.J., Sickler, R.R., Mahan, S.A., Brown, Johnathan, Reidy, L.M., and Kimball, M.A., 2012, Logs and 

data from trenches across and near the Green Valley Fault at the Mason Road site, Fairfield, Solano County, 

California, 2006–2009: U.S. Geological Survey Open-File Report 2012–1011, pamphlet 5 p., 5 sheets. (Available at 

http://pubs.usgs.gov/of/2012/1011/.) 

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

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted material contained within this report.
iii

Contents 

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

Geologic Setting and Fault Mapping .......................................................................................................................... 1

Slip Rate Investigation ............................................................................................................................................... 2

Earthquake Evidence and Trenching Methodology .................................................................................................... 2

Acknowledgments .......................................................................................................................................................... 3

References Cited ........................................................................................................................................................... 3

Tables

Table 1. Radiocarbon ages ........................................................................................................................................ 5
Logs and Data from Trenches Across and Near the 

Green Valley Fault at the Mason Road Site, Fairfield, 

Solano County, California, 2006–2009

By James J. Lienkaemper,1Robert R. Sickler,1Shannon A. Mahan, 1 Johnathan Brown, 1 Liam M. 

Reidy,2and Mindy A. Kimball3

Introduction

The primary purpose of this report is to provide drafted field logs of exploratory 

trenches excavated across the Green Valley Fault in 2007 and 2009 that show evidence for 

four surface-rupturing earthquakes in the past one thousand years. The site location and 

site detail are shown on sheet 1 (figs. 1 and 2). The trench logs are shown on sheets 1, 2, 

and 3. We also provide radiocarbon laboratory dates (table 1) used for chronological 

modeling of the earthquake history. Sheets 4 and 5 show additional data obtained in 2006–

2009 to document data obtained in our studies of the long-term geologic slip rate on the 

Green Valley Fault. However, that effort ultimately did not prove feasible and no slip rate 

estimate resulted.

Geologic Setting and Fault Mapping

The Green Valley Fault location is identified north and south of the trench site by 

aerial photo interpretation of its geomorphic expression (Wallace, 1990) and from en 

echelon cracks caused by fault creep in the asphalt-concrete pavement of Mason Road 

(sheet 1, fig. 2). The trench site is located in distal alluvial fan deposits that have been offset 

by right-lateral slip on the fault, which has formed a low scarp and subtle closed depression 

near trench 07S (fig. 2; below the resolution of the contouring, but fills seasonally with 

rainwater). Although expression of faulting in trench 07S was almost entirely obscured by 

highly bioturbated marshy soil deposits, the fault is well resolved at depth by highresolution seismic imaging (Kimball and others, 2011). Because faulting in trench 07S was 

in evidence only as a monoclinal warp (in north and south walls) yielding no evidence of 

individual earthquake ruptures, we logged only the south wall (sheet 3). In contrast, the 

fault was expressed clearly in trenches N1-N3 (sheet 1, fig. 1 inset; sheet 2) located about 

 

1 U.S. Geological Survey

2 University of California, Berkeley

3 California State University East Bay, Hayward
2

100 m to the north of trench 07S. Because there is no surface expression of the fault at this 

site, even in historical aerial photographs, we chose where to trench based on a distinct 

step in the water table across a distance of only a few meters as observed in cone 

penetration testing (Bennett and others, 2011) and supplemented by more closely spaced 

hand augering.

Slip Rate Investigation

The Mason Road site was initially selected because 1896 topographic maps showed 

a large (400-600-m) right-lateral offset of a minor stream, Hennessey Creek, suggesting 

that if this offset could be dated then we might obtain a long-term slip rate. The slip rate of 

the Green Valley Fault has nowhere been determined by local evidence, rather the slip rate

has been inferred to be 5 ± 3 mm/yr based on regional assumptions about continuity of 

observed rates on connected faults to the north and south of the Green Valley Fault

(Working Group on California Earthquake Probabilities, 2003, 2008). To determine slip 

rate, we needed to identify and to date stream sediments associated with initiation of the 

inferred offset. These sediments were expected to be approximately 100 thousand years 

old, too old for radiocarbon dating but within the range for optically stimulated 

luminescence (OSL) dating. During 2006 through 2009, we used cone penetration tests 

(CPT) and soil borings to characterize the material types and ages within the fan deposits 

near the fault and the geometry of the subsurface stream channel (for test results see 

Bennett and others, 2011). Initial results suggested an older stream channel might have 

been within reach by excavation and so, in 2006, we excavated a pit. This Mason Road Pit 

2006 map, logs, and dating results are shown on sheet 4. The OSL dates correspond fairly 

closely to radiocarbon dates (sheet 4, table 1). The pit was not deep enough to measure the 

long-term offset that we sought, therefore we used a boring to probe for possible evidence 

of channel initiation inferred from interpretation of the CPT profile to be at a depth of 12 m 

(location SNC07 in sheet 1, fig. 2; details of Core SNC07 in sheet 5, and in Bennett and 

others, 2011). However, the materials at this 12-m depth were not sufficiently old (only 

about 12,000 years old) to correlate with the large amount of offset inferred from the 1896 

map. We also attempted to image buried channel geometry using ground-penetrating radar 

(Craig and others, 2011), but the results could not adequately resolve channel structures 

much deeper than about 5-10 m. Kimball and others (2011) used high-resolution seismic 

refraction techniques that clearly imaged the fault at greater depths, thus suggesting the 

possibility that we might also be able to identify stream channels at greater depths. 

Encouragingly, in 2007, surveys east of the fault did indicate a channel at 10-15 m depths, 

however, in 2009, surveys west of the fault found no matching channel (Craig, 2010). An 

additional boring at “stake 11” location (sheet 1, fig. 2) was done but we did no additional 

dating of this buried channel because we had not found any matching offset stream channel 

deposits west of the fault.

Earthquake Evidence and Trenching Methodology

In 2007, we excavated two cross-fault trenches and three more in 2009 at the site,

seeking evidence for paleoearthquakes (sheets 1 and 2) as has been described on another 

creeping fault in the region, the Hayward Fault (Lienkaemper and others, 2002a, 2010). We 

identified evidence for a sequence of four ground-rupturing events in the past millennium
3

(Lienkaemper and others, unpub. data). Earlier ruptures could not be clearly distinguished 

or dated. The long-axes of trenches N1, N2, and N3 orient perpendicular to the fault; trench

N4 is parallel to the fault (fig. 2). Trench N4 was used to show continuity of stratigraphic 

units. The general stratigraphy is composed of a series of alluvial deposits overlying a 

marshy, bioturbated silty clay unit (u10). The alluvial deposits are characterized by 

variation between more silty and sandy units (u20, u40, u60, u80, u100) and more clayey 

organic units having varying degrees of soil development (u30, u50, u70, u90). The 

methodology used in logging the trenches is described in Lienkaemper and others (2002b). 

Logging was done on high-resolution, ortho-rectified photo mosaics of the trench walls. 

Raw radiocarbon ages are shown in table 1 below. Nine pollen samples were taken from 

trench N1 (m 0.7 in units u80, u90, and u100); however, pollen preservation was poor. The 

species of non-native pollen, Erodium cicutarium, indicative of the earliest historical period 

(about 1770-1780), was not observed in any of these samples, but the sandy material 

provided such an oxidative environment that the results are not conclusive.

Acknowledgments

This investigation was funded by the U.S. Geological Survey National Earthquake 

Hazard Reduction Program. We owe many thanks to the late Billy Yarbrough and his 

family, especially Debra and Anthony Russo, without whose continuing practical assistance, 

this work would not have been possible. Reviews by Suzanne Hecker and Dan Ponti and 

text edit by Theresa Iki greatly improved this report.

References Cited

Bennett, M.J., Noce, T.E., and Lienkaemper, J.J., 2011, Cone penetration tests and soil borings 

at Mason Road, Green Valley, Solano County, California: U.S. Geological Survey OpenFile Report 2011–1281, 52 p. 

Craig, M.S., Kimball, Mindy, and Lienkaemper, J.J., 2011, Ground penetrating radar 

surveying of the Green Valley Fault, San Francisco Bay Area, CA, in Knudsen, K., 

Baldwin, J., Brocher, T., Bürgmann, R., Craig, M., Cushing, D., Hellweg, P., Wiegers, M., 

and Wong, I., eds., Proceedings of the 3rd Conference on earthquake hazards in the 

eastern San Francisco Bay area: California Geological Survey Special Report 219, p. 

381–390. 

Craig, M.S., 2010, Near-surface geophysical imaging of paleochannels for the determination 

of slip rate at the Green Valley Fault, U.S. Geological Survey, National Earthquake 

Hazard Reduction Program, Final Technical Report for Award Number 

G09AP00077, 19 p., accessed February 22, 2011, at

http://earthquake.usgs.gov/research/external/reports/G09AP00077.pdf

Kimball, M.A., 2005, Seismic refraction on the Green Valley and Hayward Faults, San 

Francisco Bay Area, CA: California State University, East Bay, Masters Thesis. 
4

Kimball, Mindy, Craig, M.S., and Lienkaemper, J.J., 2011, Using seismic refraction to identify 

and characterize near-surface expression of active faults in the eastern San 

Francisco Bay Area, CA, in Knudsen, K., Baldwin, J., Brocher, T., Bürgmann, R., Craig, 

M., Cushing, D., Hellweg, P., Wiegers, M., and Wong, I., eds., Proceedings of the 3rd 

Conference on earthquake hazards in the eastern San Francisco Bay area: California 

Geological Survey Special Report 219, p. 369–380.

Lienkaemper, J., Dawson, T., Personius, S., Seitz, G., Reidy, L., and Schwartz, D., 2002a, A 

record of large earthquakes on the southern Hayward fault for the past 500 years: 

Bulletin of the Seismological Society of America, v. 92, no. 7, p. 2637–2658.

Lienkaemper, J., Dawson, T., Personius, S., Seitz, G., Reidy, L., and Schwartz, D., 2002b, Logs 

and data from trenches across the Hayward Fault at Tyson's Lagoon (Tule Pond), 

Fremont, Alameda County, California: U.S. Geological Survey Miscellaneous Field 

Studies Map MF–2386, 12 p., 2 plates, accessed February 22, 2011, at 

http://pubs.usgs.gov/mf/2002/2386/.

Lienkaemper, J.J., Williams, P.L., and Guilderson, T.P., 2010, Evidence for a 12th large 

earthquake on the southern Hayward fault in the past 1900 years: Bulletin of the 

Seismological Society of America, v. 100, no. 5A, p. 2024–2034.

McFarland, F.S., Lienkaemper, J. J., and Caskey, S.J., 2009, Data from theodolite 

measurements of creep rates on San Francisco Bay region faults, California, 1979–

2009: U.S. Geological Survey Open-File Report 2009–1119, version 1.2 (2011), p. 17, 

accessed April 5, 2012, at http://pubs.usgs.gov/of/2009/1119/. 

Prescott, J.R., and Hutton, J.T., 1994, Cosmic ray contribution to dose rates for luminescence 

and ESR dating; large depths and long-term time variations: Radiation 

Measurements, v. 23, p. 497–500. 

Stuiver, M., and Polach, H., 1977, Discussion; reporting of 14C data: Radiocarbon, v.19, p. 

355–363.

U.S. Geological Survey and California Geological Survey, 2006, Quaternary fault and fold 

database for the United States: U.S. Geological Survey and California Geological 

Survey, accessed February 22, 2011, at 

http://earthquake.usgs.gov/regional/qfaults/. 

Wallace, R.E., 1990, Geomorphic expression, in Wallace, R.E., ed., The San Andreas Fault 

System, California: U.S. Geological Survey Professional Paper 1515, p. 14–58.

Working Group on California Earthquake Probabilities, 2003, Earthquake probabilities in 

the San Francisco Bay Region; 2002–2031: U.S. Geological Survey Open-File Report

2003–214, accessed February 22, 2011, at http://pubs.usgs.gov/of/2003/of03-214/.

Working Group on California Earthquake Probabilities, 2008, The uniform California 

earthquake rupture forecast, version 2 (UCERF 2): U.S. Geological Survey Open-File 

Report 2007–1437, February 22, 2011, at http://pubs.usgs.gov/of/2007/1437/.
Sample 

no.1 Material 14C age (yr) BP2 Unit no. (u#) Expos. 

-Wall3

Location 

(m) ∂13C4 Fraction modern ∂14C Lab. no.5

07N24 charcoal 670 ± 30 u100 N1-n 7 -26.1 0.9198 ± 0.0031 -80.2 135766

07N13 charcoal 480 ± 35 u80 N1-n 4 -25 0.9422 ± 0.0036 -57.8 137742

07N14* charcoal 530 ± 30 u80 N1-n 4 -24.8 0.9360 ± 0.0031 -64.0 135763

07N03 charcoal 1700 ± 60 u80 N1-n 0 -25 0.8088 ± 0.0053 -191.2 137741

07N01 charcoal 2480 ± 270 u80 N1-n 0 -25 0.7342 ± 0.0246 -265.8 137740

07N26 charcoal 800 ± 30 u70 N1-s 9 -25 0.9054 ± 0.0032 -94.6 135767

07N20 charcoal 815 ± 35 u70 N1-n 6 -25 0.9037 ± 0.0036 -96.3 135765

07N29 charcoal 845 ± 35 u70 N1-n 9 -25 0.9002 ± 0.0036 -99.8 135768

07N15a* charcoal 865 ± 30 u60 N1-n 4 -24.4 0.8982 ± 0.0030 -101.8 135764

07N15b charcoal 880 ± 30 u60 N1-n 4 -24 0.8961 ± 0.0030 -103.9 135998

N3-2a charcoal 745 ± 30 u50 N3-n 5 -25 0.9116 ± 0.0033 -88.4 145907

N3-2b charcoal 865 ± 40 u50 N3-n 5 -25 0.8978 ± 0.0041 -102.2 145912

N3-4 charcoal 1060 ± 30 u50 N3-n 7 -25 0.8766 ± 0.0032 -123.4 145908

07N08b charcoal 900 ± 35 u40 N1-s 1 -25 0.8941 ± 0.0035 -105.9 135770

07N08a* charcoal 950 ± 30 u40 N1-s 1 -24.6 0.8885 ± 0.0030 -111.5 135761

07N10* charcoal 1005 ± 30 u40 N1-n 2 -25.6 0.8826 ± 0.0028 -117.4 135762

N3-1a charcoal 950 ± 35 fissure in u30 N3-n 5 -25 0.8885 ± 0.0035 -111.5 145906

N3-1b charcoal 970 ± 35 fissure in u30 N3-n 5 -25 0.8865 ± 0.0035 -113.5 145911

N2-2 bulk 640 ± 180 u30 N2-n 6 -25 0.9230 ± 0.0197 -77.0 145914

N3-5 charcoal 1290 ± 35 u30 N3-n 10 -25 0.8515 ± 0.0035 -148.5 145909

N2-1 charcoal 1015 ± 35 u30 N2-n 6 -25 0.8813 ± 0.0036 -118.7 145910

07N31* bulk 1810 ± 30 u10 N1-s 2 -25.8 0.7984 ± 0.0027 -201.6 135769

MR07-06a charcoal 10,905 ± 35 –– SNC7 –– -25 0.2574 ± 0.0011 -742.6 137744

MR07-06b charcoal 10,970 ± 35 –– SNC7 –– -25 0.2553 ± 0.0011 -744.7 135772

MR07-09a twig 10,950 ± 35 –– SNC7 –– -25 0.2558 ± 0.0011 -744.2 135773

MR07-09b bulk 14,015 ± 45 –– SNC7 –– -25 0.1747 ± 0.0009 -825.3 135771

MRP-4 charcoal 840 ± 35 pit-35 06Pit –– -25 0.9005 ± 0.0036 -99.5 129414

MRP-7 charcoal 950 ± 30 pit-45 06Pit –– -27.0 0.8887 ± 0.0029 -111.3 129415

MRP-3 charcoal 3085 ± 30 pit-70 06Pit –– -26.6 0.6813 ± 0.0022 -318.7 129413

MRP-8 bulk 6335 ± 45 pit-80 06Pit –– -25 0.4543 ± 0.0025 -545.7 129416

Table 1. Radiocarbon ages.

1

a,b,c - indicates a dated split of a sample. Samples marked with * have had a ∂13C split taken to confirm the estimate of -25‰ 

2

±1σ-age in radiocarbon years using the Libby half life of 5568 years and following the conventions of Stuiver and Polach (1977) 

3

±Expos., exposure: Trenches N1, N2, N3; 2006 Pit; Core SNC007; -n, north wall; -s, south wall 

4 ∂13C values are the assumed values according to Stuiver and Polach (1977) when given without decimal places.

5

All ages obtained by AMS analysis at Center for Accelerator Mass Spectrometry (CAMS), Lawrence Livermore National Laboratory, Livermore, California

5