division of mines and geology -...

STAiC OF CAUFORNIA-fHC RESOURCES AGENCY

DEPAIHMeNT OF CONSERVATION

DIVISION OF MINES AND GEOLOGY BAY AREA REGIONAL OFFICE 1145 MARKET STREET, 3RD FLOOR

SAN FRANCISCO, CA 94103-1513

PHONE: (41.S) 557-1500

ATS$ .59?'· 1500

William L. Selleck Planner III Conservation - Development

and Planning Commission ll95 Third street Napa, CA 94559-3092

Dear Mr. Selleck:

• • ro-erc WILSON, G"'vt!'rm;ir

January 2, 1992

We are placing on open file the following report, reviewed and approved by the County of Napa in compliance with the AlquistPriolo Special Studies Zones Act:

Geologic hazards investigation, Green Island Industrial Park, Struble property, Napa Co., CA; by Bailey Scien~ific; 8/9/91.

This report refers to a 1989 Earthtec report for the same site. Since that report has trench and other information on the site, I believe it would be appropriate to file that report as part of this public file. I would appreciate it if you would make a copy of the Earthtec report and send it to me.

Another report also was referred to in the Bailey report and that is a 1983 report by Darwin Myers on Napa Airport study Area. Would it be possible to obtain a copy of the latter report for our reference?

EWH:ra cc: A-P file"'

Sincerely,

Cltft-EARL W. HART, CEG 935 Senior Geologist &

Program Manager

JEFFREY R. REDDING Secretary-Director

NAPA COUNTY

December 27, 1991

Earl W Hart

CONSERVATION - DEVELOPMENT

AND PLANNING COMMISSION

1195 THIRD STREET• NAPA, CALIFORNIA 94559-3092 AREA CODE 7071253-441 6

CALIFORNIA DIVISION OF MINES & GEOLOGY 1145 Market Street-Third Floor San Frnncisco, CA 94103-1513

RE: Alquist Priolo Geologic Hazard EvaluationStruble Land Division

Dear Mr, Hart:

Pursuant to Section 3602(c) of the California Administrative Code, please find enclosed a copy of the above referenced geologic hazard evaluation. Also included for your information is a copy of the review thereof prepared by Certified Engineering Geologist Darwin Myers. This review found that the submitted report satisfies the requirements of the Alquist-Priolo Special Studies Zones Act.

If you have a need any further information, please feel free to call me.

Respectfully Yours,

WILLIAM L, SELLECK Planner III

cc: Mike Miller, Deputy Director Wilson Aguillon, Project Engineer(Northpoint Engineers)

AP-RPT.TRN

.• '

DARWIN MYERS ASSOCIATES

ENVIAOr.iMENTAL RESEARCH • ENGINEERING OEOLOGY

27 September 1991

William L. Selleck Environmental Analyst Conservation - Development

and Planning Department 1195 Third Street, Room 210 Napa CA 94559-3092

Subject: Review of Alquist-Priolo Report APN 58-330-03 Struble Land Division Green Island Area, Napa County

Dear Mr. Selleck:

At your request, we reviewed a report prepared by Bailey Scientific, entitled "Fault Hazards Investigation, Struble Property, Parcel "B", Green Island Road, Napa County, California" (dated 9 August 1991).

BACKGROUND

The report evaluates the hazard of surface fault rupture of a 15.24 acre parcel that was previously investigated by Earthtec (1989). The Earthtec report interpreted features in the eastern portion of the site to be evidence of faulting.

Our firm reviewed and approved the Earthtec report, but we did not have the opportunity to observe their trenches, and evidence of active faulting did not appear to be conclusive. Based on the data gathered, Earthtec recommended setback from the feature. Because the consultant recommended regulation of land use, further evaluation of the Earthtec fault was not deemed necessary, and hence the report was approved.

Subsequently the owner, Mr. Struble, retained Bailey Scientific to determine if further studies might more accurately establish the significance of the "fault" mapped by Earthtec. Bailey Scientific invited me to observe exposed conditions in the trenches, and for three days we viewed these conditions with Mr. Bailey.

1308 PINE STREET • MARTINEZ, CA 94553 • 4151370-9330

SCOPE

The scope of the subsurface investigation included the logging of 1650 lineal feet of exploratory trenches, along with 1350 linear feet of magnetometer profiles. Plate l of the Bailey Scientific report shows the location of their trenches and geophysical traverses, along with the fault zone mapped by Earthtec. Note that Trench B crosses the Earthtec fault zone, and that Trenches A and B "shadow" 100% of the Struble parcel. Additionally, Trenches C, D and E were logged to provide additional confirming evidence on interpretation of geologic features seen in Trenches A and B.

FINDINGS OF BAILEY SCIENTIFIC

The primary products of the investigation performed by Bailey Scientic are an original geologic map of the site (Plate 1) and a structure section (Figure 7). These illustrations present an interpretation of site conditions that show an overturned, northwest trending anticline on the property. Shearing was observed in the core of the anticline. It is attributed to a brittle response of the rock to tight folding. The anticline is not associated with any known lineaments; it is outside the Special studies Zone and Bailey Scientific observed no evidence that the soil horizon is offset. For those reasons, the shearing observed in the core of the anticline is not considered to be evidence of active faulting.

Bedding was difficult to discern in the trenches because the unit referred to as the Huichica Formation by Bailey Scientific is massive and lithologic contacts are gradational. The geologic contacts that were present generally lacked the primary sedimentary structures used to establish the direction of stratigraphic younging. Consequently the interpretation Of overturned beds is based on the geologist's conception of stratigraphic units, and not on primary sedimentary structures. The formations mapped are a continental deposit of inferred Late Pliocene - Early Pleistocene age, and a marine unit within the Great Valley Sequence (Cretaceous). Descriptions of these stratigraphic units are presented in both the text of the report and in the trench logs.

with regard to the Earthtec fault, Trench B crossed this fault near station 7+60 (see Plate 4 for log of this interval). Bailey Scientific mapped a disced horizon overlying a well developed B horizon. The log indicates the B horizon is approximately 3 feet thick, and underlying this soil is the Huichica Formation, which is described as a dark gray-brown and dark gray, mottled, massive clay with disseminated organic matter and caliche. No ground water or shearing was observed in this unit. The presence of a well developed soil profile, along with a smooth, relatively horizontal soil/bedrock contact were interpreted as evidence of an unfaulted, deeply weathered bedrock. We observed exposed conditions in this trench, and our observations are consistent with

,I!"", DARWIN MYFRS ASSOCIATES .,--·· ·--- ·---

•

the features shown on the trench log, We did not see evidence of the Earthtec fault,

CONCLUSIONS OF THE REVIEWER

In our opinion the report presents sufficient data to be a basis for reevaluating site geologic conditions. Moreover, the report is consistent with the CDMG guidelines for evaluating the hazard of surface fault rupture. Bailey scientific concludes that there is no evidence of active fault rupture on the property. on that basis, it is our opinion that the Bailey Scientific report satisfies the requirements of the Alquist-Priolo Act. It is our further opinion that regulation of land use along the Earthteo fault is not warranted.

If you have any questions on the geologic report or the review, please call.

Sincerely,


Da~~46 Principal

ii!"""'. DARWIN MYERS .ASSOCIATFS .,;-

I I I I I I I I I I I I I I I I I I I

BAILEY SCIENTIFIC

Project 378

tf fl z,G.r4

R i::,... r:: ~ '' r:: D AUG i ;l 1991

GEOLOGIC HAZARDS INVESTIGATION

STRUBLE PROPERTY, PARCEL •a•

GREEN ISLAND ROAD

NAPA COUNTY, CALIFORNIA

9 August 1991


BAILEY SCIENTIFIC

Mr. Lester Struble 876 Green Island Road Vallejo, CA 94589

603 WALNUT DRIVE• SUISUN, CA 94585-1555 (707) 864-5419

August 9, 1991

Subject: Geologic Hazards Investigation Green Island Industrial Park Struble Property Napa County, California

Dear Mr. Struble:

We are pleased to submit seven copies of our geologic hazards report for your property (Parcel "B"). This investigation has considered geologic hazards as outlined by the State of California, Division of Mines and Geology Note 37.

Of particular concern in this investigation is the mapped trace of the West Napa fault which passes to the east of your property. Although your property is not transected by the fault, the easterly portion of the property is included within the Special Studies Zone (Alguist-Priolo Act) assigned to this fault by the California Division of Mines and Geology.

Additionally, a previous study of your property by Earthtec, Ltd., in 1989, concluded that an active fault occurs on the easterly portion of your property.

Our study included: review of published and unpublished literature, photogeologic interpretation, a geologic reconnaissance, exploration trenching and logging, sampling for pollen identification and possible dating of selected geologic units, a ground-magnetic survey, and the production of this report.

The following conclusions and recommendations are made as a result of our study.

1. No evidence was found that would lead to the conclusion that a fault occurs on the property.

2. No geologic hazards were found to materially threaten the property.

3. A northwesterly-trending anticline with an overturned westerly limb occurs in the approximate middle of the property.


4. As with all of California, the site will be subject to seismic shaking; however, due to the presence of the competent materials of the Huichica formation and the Great Valley sequence, no amplification of seismic energy is expected at the site.

5. Trenches were back-filled but not to engineering standards. This factor should be taken into account for proposed structures.

6. The expansive nature of the soil at the site should be accounted for in the foundation design of proposed structures.

7. The site is considered to be aptly suited for development.

We are appreciative of this opportunity to be able to provide our geological/geophysical services for this project. In the event there are questions, or should additional information be required, we welcome your contact.

ADB:fb Enclosure

Respectfully submitted,

D. Bailey Certified Engineering Geologist No. 762


TABLE OF CONTENTS

Introduction

Site Description

Field Work

Regional Geology

Previous Investigations

Magnetic Survey

Stratigraphy

Structural Geology

Photo-Geologic interpretation

Seisrnicity

Geologic Hazards

References

LIST OF ILLUSTRATIONS

l Regional Geologic Map

2 Regional Fault Map

3 Special Studies Zone Map

Page

l

1

2

3

5

10

11

13

15

15

16

19

4 Location of Previous Investigations

5 Regional Epicenter Map

6 Magnetic Traverses 1, 2, and 3

7 Geologic Cross-Section

Plate l

Plates 2-5

Appendix A

Appendix B

Site/Geologic Map -- Pocket

Trench Logs 1'A 11-'

1 E 11 -- Pocket


Introduction

In accordance with your request, an investigation has been

made of the subject site for the purpose of determining its

geologic characteristics and, by extension, its potential for

producing geologic hazards. Of particular interest is the

investigation into the possible presence of the West Napa fault

which has been mapped approximately 300 ft. to the east of the

site by the U.S. Geological Survey. A portion of a Special

Studies Zone (SSZ), assigned by the State of California's

Division of Mines and Geology to this fault, intersects the

easterly quarter of the site. This jurisdiction, defined by the

Alquist-Priolo Act (1973), requires an investigation into

potential geologic ha7-ards within the SSZ. In the course of an

investigation the presence or absence of a fault is determined

and, if present, an effort is made to date its last movement in

order to ascertain if the fault is of Recent (movement within the

last 11,000 years) age. Such faults are judged to be ''active"

and require special considerations regarding structures.

The study of the site has included: \ 1 . a geo og1c

reconnaissance, exploration trenching and logging, a ground

magnetic survey, review of pertinent geologic literature and

unpublished reports, aerial-photo interpretation, selected

sampling for pollen dating, and the production of this report.

This study follows that of Earthtec Ltd. whose report (1989)

states that an active fault passes through the easterly portion

of the site.

Site Description

The 13.3A site (Parcel "B") is located on Green Island Road,

1

I I I I I I I I I I I I I I

It is north of the City of Vallejo and west of State Highway 29.

polygonal in shape, being bordered on the north by Southern

Pacific railroad tracks, on the west and south by Green Island

Road, and on the east by Parcel "A" where the residence and

outbuildings of Mr. Struble are located. A separately owned

residential plot occurs in the northwest corner. The parcel has

a slight rise to the northeast (el. 26 to el. 41) with a low

northwest trending ridge occurring at the northerly boundary. No

drainages or other noteworthy topographic expressions exist on or

adjacent to the site. The land has been used for hay production.

The site is across Green Island Road from the northwest

corner of the Panattoni property which our firm investigated for

geologic hazards in 1989. The Price property, another of our

investigations (1990) abuts the easterly end of the Panattoni

property. No evidence indicative of faulting was observed on

either of these two sites. For locations see Figure 3. For

location and details of the Struble property refer to the

"Site/Geologic Map," Plate 1 (base map supplied by Northpoint

Engineers, Inc.). The location of Earthtec's mapped fault trace

and the SSZ are also shown on this map.

Field work

The field work consisted of a geologic reconnaissance of the

site and surrounding area, a ground-magnetic survey, and

exploratory trenching.

Five exploration trenches, 11 A1'-

11 E,'1 were excavated on the

I site by an Allis Chalmers Model 580K back-hoe with a 3-ft. wide

I I I I

bucket. The initial intention was to excavate Trench "A" from the

southwest corner of the property to the northeast corner.

However, the encountering of slickensides (physical expression of

shearing) and a previously excavated test pit prompted the

excavation of four other trenches in order to determine the

extent and origin of the slickensides which are commonly produced

2


by tectonic forces associated with faulting and folding.

The trenches were excavated at a rate such that relatively

fresh surfaces would be exposed for logging, thus drying of the

trench walls was kept to a practical minimum. Where necessary

the walls were scraped to expose fresh surfaces for analysis.

Trenches were back-filled and wheel rolled; they were not

compacted to engineering standards.

The magnetic survey was conducted with a portable, proton

precession magnetometer (Geometrics, Model G-856X) which measures

the local magnetic field to within one-tenth gamma; readings were

taken at intervals of 10 feet. Upon completion the magnetic

field of the base station (first reading) was re-measured to

correct for possible magnetic drift due to solar micropulsations

and magnetic storms. The survey was conducted in the effort to

determine the magnetic signature of the earth materials in the

likelihood that should a fault be present on the property it

could be located by a resulting anomaly which could be

magnetically mapped.

Bulk samples were taken of the soil and other earth

materials at selected locations for pollen analysis and possible

dating. However, the pollen tests (external shells) were found

to be too badly deteriorated for identification.

Regional Geology

The site lies within the northern section of the California

Coast Ranges which principally are a aeries of northwest-trending

parallel to sub-parallel valleys and ridges which occur from the

Great Valley to the Pacific Ocean. Within this province 1s

contained the Diablo Antiform, so named by Bailey et al. (1964)

for the northwest trending tract of en echelon-folded (some

overturned) rocks which occur from Parkfield on the south to

Clear Lake on the north and from the Hayward fault on the west to

3


the Great Valley on the east. The antiforms (in some cases the

sedimentary sequences are unknown) are commonly pierced by the

underlying Franciscan formation -- the Franciscan piercement of

Mount Diablo (anticline with one limb overturned) being the most

dramatic. Northeast-southwest compressive forces, occurring in

the Late Pliocene to at least the Late Pleistocene (likely extend

to today), have produced the complexly-folded Diablo antiform

whose development has been essentially coeval with the building

of the Coast Ranges.

The site is located on a small rise above the Napa River

delta which is believed to have been primarily produced during

the last pluvial/glacial maximum (Late Wisconsin/Late

Pleistocene) by the alluvium transported down the Napa River and

local, smaller drainages -- all of which eventually emptied into

San Pablo Bay. In this relatively low-energy environment, fine

grained continental sediments (mostly alluvial fans) were laid

down, interfingering with marine deposits at the edge of the

delta whose position and characteristics changed as the dynamics

of mountain-building and sea-level fluctuations interplayed.

Within this delta is Oat Hill and the shallow rise upon which the

subject site is located. Oat Hill, approximately one-half mile

southeast of the site (Plate 1), is a bedrock prominence of

contorted fine-grained sedimentary rock that has been assigned to

the Unnamed formation of the Jurassic-Cretaceous age Great Valley

Sequence of marine origin. Along a portion of the easterly flank

of Oat Hill and extending under the plain is the marine sandstone

of the Domengine formation. At the toe of the flank commonly

occurs a scattered veneer of colluvium which extends onto the

alluvium found in the adjacent flat area. The ''Regional Geologic

Map" (Figure 1) reveals the contacts between the Unnamed

formation (kJgum), the Domengine formation (Ted), and young

alluvial fan materials (Quf) mapped by Sims et al. The

orientation of the contact between the Domengine and Unnamed

formations, as well as bedding attitudes in cuts along the

easterly flank of Oat Hill, indicate a northwest strike for these

4


two rock units, essentially paralleling the West Napa fault as

mapped (see Figures? and 3). The West Napa fault has been

mapped as a contact between these two formations as well as being

coincident with the photolineament produced by their contact.

Previous Investigations

The site is in the vicinity of previously conducted regional

and site-specific studies. Both types of studies are addressed

in this report.

Weaver (1949) mapped nine quadrangles north of San Francisco

and included the rocks at Oat Hill in the Jurassic-Cretaceous

Knoxville and Horsetown formations (undifferentiated) which are

principally composed of shale (upwards of 95% according to

Weaver) with occasional layers of graywacke sandstone and

limestone layers/lenses. Weaver noted that carbonaceous matter

is occasionally found along the bedding planes of the sandstone.

Weaver did not map a fault in the area of Green Island Road,

nor did he map the West Napa fault.

Brown (1970) mapped an area surrounding the San Francisco

Bay that covers approximately 5100 square m~les. He mapped

historically active (movement within the last 200 years) faults

and those that express geologically young surface displacement

and, based upon these criteria, did not map the West Napa fault.

Sims et al. (1973) mapped Solano and parts of Napa (includes

the site), Contra Costa, Marin, and Yolo Counties and did not map

a fault in the vicinity of the site, nor did he map the West Napa

fault. Sims et al. maps the contact between the unnamed and

Domengine formations as conformable.

shown in Figure 1.

A portion of this map is

In 1975 the Division of Mines and Geology, under the

5


direction of Charles w. Jennings, produced a fault map of the

State of California. This map isolates historic (movement within

the last 200 years) and Quaternary (movement within the last 2

million years) faults and does not show a fault through or near

the subject site. In addition the "Geologic Map of California,"

1977, also produced by the Division of Mines and Geology, does

not show a fault through or near the site.

Helley and Herd (1977) mapped a 68 mile x 62 mile area that

contains the City of Vacaville at its center and includes the

project site. This work shows faults which, in the opinion of

the authors, express evidence of Quaternary (last 2 million

years) displacement and includes the West Napa fault (originated

in this work) as shown in Figure 2. Helley and Herd mapped

faults based upon interpretation of aerial photographs and the

alignment of surface features such as tonal variations and

topography, the latter exemplified by linear troughs and ridges

and aligned saddles and notches. It is their belief that the

West Napa fault expresses geomorphic evidence of having

experienced Holocene movement, that is, within the last 10,000

years. However, they do not report direct evidence for the

establishment of the West Napa fault, but rather define it based

upon their inferential information. They have mapped a short

segment of this fault through the subject site as shown in Figure

2 •

Subsequent to the establishment of the West Napa fault by

Helley and Herd and the assignment of a Special studies zone by

the Division of Mines and Geology, this postulated fault has been

investigated by a number of geotechnical firms for projects

located within the ssz. Figure 3 shows the location of the site

relative to the West Napa fault as shown on the State of

California's Special Studies Zone map for the Cuttings Wharf

Quadrangle. Figure 4 illustrates the locations of previous

geotechnical investigations conducted in the area. The reports

of other investigators were obtained from the Conservation,

6


Development, and Planning Department of the County of Napa. The

reports for these projects were reviewed and are discussed below

in numbered order as shown in Figure 4. In addition the comments

of the county's peer-review geologist, Darwin Myers, were also

perused.

Earthtec (1) 1 1989, investigated the subject site. The

Earthtec report states that a fault, based upon the results of \

their trenching and photogeologic interpretation, is located in I

the easterly portion of the site (see Plate 1). However, the. I report does not define the trace in the amount of detail requ1re4

for conclusive mapping. In general, the information presented irt I

the report, logging detail, geologic coverage, and trench

placement and extent were not sufficient to addeguately support

the conclusions regarding faulting. This general view is

supported by Mr. Myers in his letter (on file with Napa County)

which summarizes his review of the Earthtec report.

mapped fault is shown in Plate 1.

Earthtec's

Kleinfelder & Associates (2), 1983, studied a site located

southeast of the project and mapped a trace of the West Napa

fault in its southwest quadrant. Their report does not describe

the trench geology sufficiently to confirm the presence of the

fault which the report states was found. The location of their

fault was not drawn or described in the trench log, the trench

log was diagrammatically drawn; and the report was not signed by

the responsible geologist. As a result the reliability of this

report is seriously questioned and the establishment of a fault,

as presented, is not supported by the report.

Thomas D. Hays & Associates (3), 1982, investigated a tract

of land immediately west of the subject site and west of the SSZ.

This investigation did not utilize trenching and concluded that

no evidence was found which would conclude that faulting occurred

on the property.

7


Envii:-onmental Management and Research, Inc., ( EMRI) ( 4),

1979, investigated the Panattoni site and included exploration

trenching and a ground magnetic survey in their study. A trench

was excavated across each of the three West Napa fault traces

mapped by Helley and Herd (1977). In addition a magnetic

traverse was likewise positioned. In the opinion of the EMRI

engineering geologist, no evidence that is suggestive of a fault

was produced by these investigative methods.

Our firm, in 1989, also investigated the Panattoni site for

geologic hazards, specifically for the West Napa fault.

Following the excavation and logging of a 2000 ft.-long trench

and the completion of a ground-magnetic survey, the conclusion

was drawn that no fault-related evidence had presented itself.

In addition, the alluvial fan deposits, based upon soil

morphology, are considered to be older than 11,000 years. Should

the West Napa fault be present at depth, the age of the overlying

deposit would indicate that the fault is inactive according to

the 11,000 year criterion imposed by the California Division of

Mines and Geology.

Kleinfelder & Associates (5), 1984, investigated a plot of

land which encompasses a large portion of Oat Hill and, in the

northeast corner, includes traces of the West Napa fault as

mapped by Helley and Herd. They excavated a trench across this

mapped trace and found bedrock shears but did not encounter a

fault, in their opinion. Additional trenching on the westerly

side of Oat Hill, across a photolineament, intercepted a geologic

feature which the report states is likely an active fault but was

not definitively defined nor dated by this investigation. No

attempt was made by Klein£elder & Associates to extend this

geologic feature beyond their study boundary.

Balbi & Chang Associates (6), 1983, made a geologic as well

as a foundation investigation for industrial structures.

Utilizing sampled borings, aerial photographs, and a literature

8

I I I

search, they did not determine that a fault transects the

property.

Darwin Myers Associates (7), 1983, conducted a geologic

I study of the Napa County Airport located approximately one mile

north of the subject site. A photolineament map from the Darwin

I I I I I I I I I I I I I I I

Myers Associates' report is included as Appendix A. A

discontinuous photolineament that is congruent with the fault as

mapped by Helley and Herd (1977) passes nearby to the east of the

site. This photolineament is expressed by linear topography,

drainages, and linear tonal change. The trench log of Darwin

Myers Associates depicts a very steep contact between two

colluvial units. The contact strikes Nl8°W and dips

approximately 75°W. Although no shears or slickensides were

found along this contact, shears of Nl4°W/60°W were measured in

the soil above the contact. Such features and their association

were inferred by the firm as being "fault related," but were not

identified as being a fault. No evidence for surface fault creep

was found according to this report.

Bailey Scientific (8), 1989, conducted a geologic hazards

investigation on the Price- property. The study included a

ground-magnetic survey along with a seismic survey (for

excavation estimating), a site and local ge~logic reconnaissance,

photo-geologic interpretation, and a literature review (including

local geologic/geotechnical reports on file with Napa County).

No evidence was found which was interpreted as being

representative of a fault or related to a fault.

William A. Bryant, geologist with the California Division of.

Mines and Geology, produced a Fault Evaluation Report (FER-129,

dated 13 April 1982) for the West Napa fault. As with Helley and

Herd (1977) he bases the establishment of the West Napa fault on

geomorphic features and tonal photolineaments. Bryant judged

that geologic evidence northwest of the Napa River was

insufficient to establish a ssz for the west Napa fault, but that

9

I I I

to the southeast of the river the evidence was considered

sufficient for such an establishment.

Taber Consultants, although not conducting a study in the

I area, in 1987 inspected for the Napa County Department of Public

Works the trench walls of the sewer line on the south side of

I I I

Green Island Road in the area of the pump station located in the

southwest quadrant of the intersection of Green Island Road and

Commerce Boulevard, directly south of the southeast corner of

Parcel ''B" of Struble.

The portion of the trench inspected was from Sta. 16+00 to

18+20; this portion is located in Plate 1, "Site/Geologic Map."

I Their report states that siltstone and shale occur beneath seven

to 12 ft. of soil and alluvial materials, and that the observed

I I I

materials appear to represent a "normal depositional sequence,

and no evidence of faulting (e.g., displacement of individual

soil layers, abrupt changes in color/texture, etc.) was noted."

Magnetic survey

The location of the three magnetic traverses conducted for

I this investigation are shown on the "Site/Geologic Map,'' Plate 1.

I I I I I I I

Magnetic Traverse 1, "MAG-1," was performed across the property

(Parcel "B") in order to completely "shadow'' the site and to

cross the mapped fault trace of the Earthtec, Ltd., report.

Magnetic Traverse 2, "MAG-2,'' was located parallel and northwest

of "MAG-1 1 " while Magnetic Traverse 3, ''MAG-3,'' was positioned to

the southeast of the previous two traverses and parallel to

Trench 11 D.u For details of the survey, refer to Figure 6.

The magnetic data are scattered largely

range and(dc;---;:;-o-t--produ~-;, a~---~~;,-?~~B,)iy that can

three traverses.

10

I I Stratigraphy

I since the descriptions of the geologic units are detailed in

the trench logs (Plates 2-5), they will not be repeated here 1 but

I rather their provenance and stratigraphy will be discussed in

order to produce a geologic model for the site.

I I I

Four basic types of earth materials were encountered: fill,

soil, Huichica formation sediments and sedimentary rocks of the

Great Valley Sequence.

Fill is restricted to the back-fill of exploration trenches

previously excavated by Earthtec. These excavations were I encountered in Trenches ''A,'' 1'C, 11 and 11 E 11 and are so noted in the

I I I

trench logs. The fill is a mixture of the excavated materials as

well as hay stems and roots.

The soil units consist basically of a surficial ''E"

(elluviated) horizon that has been disturbed by agricultural

discing. Beneath this unit is the undisturbed "E" horizon

followed by the ''B" (illuviated) horizon with its high clay

content due to the accumulation of translocated clays. Where I horizons laterally grade (facies change) to another definable

material the new unit is noted by the addition of a subjacent

I letter (e.g., "3A").

I I I I I I

The soil found in the excavations is typical for the area

and the underlying parent material, that is, a surficial leached

horizon (Units 1 and 2) and an underlying accumulation layer of

bentonitic/smectitic clays derived from the volcanic ash found in

the underlying Huichica formation (parent material for the

formation of the soil). The "B" horizon grades laterally to a

sandy clay and fine-grained clayey sand over rocks of the Unnamed

formation. Desiccation cracks up to one-half inch wide and

extending to l~ ft. or so are commonly found on the site and in

the surrounding area in the summer and attest to the expansive

11


nature of these materials.

The Huichica formation is believed to span parts of two

epochs; deposition is believed to have started in very late

The Pliocene time with most occurring during the Pleistocene.

formation is a sequence of continental and brackish water

fluviatile volcaniclastic sediments derived primarily from the

Sonoma volcanics (Plio-Pleistocene age), although Great Valley

sequence rocks contribute where these sediments occur in the

uplands of the Huichica basins. Because the Great Valley

sequence is composed of shales, mudstones, and fine-grained

sandstones, the detritus from these rocks is therefore fine

grained and thus not readily identifiable in the Huichica except

immediately above its contact with the Great Valley rocks where

detrital fragments are preserved, such as observed at these

contacts in the trenches of this study. Above this basal

environment the Great Valley sequence contributes only clay and

silt while the coarser detritus is derived solely from the Sonoma

volcanics, although the volcanics also contribute silt and clay.

The presence

(bentonitic) upon

of volcanic ash has produced smectitic clays

weather i nq. The result has been tn-e··-aawnward ··- ..

movemiitn\t of these clays and the production of the horizonation .-·

effect that is part of the soil morphology and weathered zone of

the underlying parent material.

depth.

This effect diminishes with

The Huichica formation was formed in a dynamic environment

controlled in large part by waning volcanism (primarily ash

falls) and the tectonism that built the Coast Ranges (very late

Pliocene to late Pleistocene). As with its correlative, the Glen

I Ellen formation, the Huichica is composed of lenticular tongues

and beds of gravel, sand, silt, and clay which vary widely in

I thickness and grade, both laterally and vertically, over short

distances into one another. Hiatuses are common while tuffs and

I reworked tuffs are found throughout. The formation lies

I 12

I I I I I I I

unconformably on the Sonoma volcanics as well as interf ingers

with its upper portion. At our site the Huichica lies in

unconformable contact on Great Valley sequence rocks.

The Great Valley sequence is represented at the site by a

fine-grained silty micaceous sandstone with a significant

feldspar fraction. This rock is massive, well-fractured, and

contains a few siltstone lenses and numerous calcium carbonate

veinlets. It is correlated with the Unnamed formation found on

Oat Hill, although Sims et al. speculate that the Domengine

formation (Ted?) occurs at the site (see Figure 1). The

Domengine is a light brown-gray and yellow-brown fine-grained

quartz sandstone -- quite a different lithology from the rocks of

I the Unnamed formation.

I I I I I I I I I I I

At its contact with the Huichica, the unnamed formation is

clayey -- a buried "C" soil horizon. Further evidence of an

unconformable contact is the yellow-red buried soil (Unit 5A)

horizon found in Trench "D.''

Structural Geology

No evidence has been found which woul~ lead to the

conclusion that a fault is present on the site, however,

structural evidence, in addition to that presented in the

"Stratigraphy" section, has been encountered which supports the

view that intense folding occurs on the property.

' Intense folding is commonplace throughout the Diablo

antiform -- a broad anticlinal structure with abundant parallel

and en echelon folds. The fold axes shown on the eastern edge of

Figure 1 are typical of the closely-spaced folds found within the

Diablo antiform block. Further examples of the severe folding in

this block are the overturned synclines which have produced Napa

and Sonoma valleys as well as countless smaller appressed folds

13

I I I I I I I

found within the block. It is not uncommon to observe horizontal

strata adjacent to tight folds in road cuts in both the Glen

Ellen and Huichica formations and the Sonoma volcanics.

' r' ·i'~t . /J As shown on the "Site/Geologic Map," Plate 1, and in the I ,,,,,,r,,_,:<-;.,p,,-

: "' -p.·1 A logs of Trenches 11 A," "B1 11 "D," and "E," a northwest striking _i .;,;t·.;y!!f"4· ·-anticline with an overturned western limb occurs near the center:--~

of the property, incorporating both the tluichica and Great Valley

units. The strike of the anticlinal axis is coincident with the

prevailing northwesterly strike of a preponderance of the folds

and faults that occur within the Diablo antiform.

The geologic cross-section shown in Figure 7 portrays the

I structure of the site as interpreted from the geology exposed in

I I I I I I I

the exploration trenches. Due to the massive nature of the

Huichica sediments (no bedding planes except at member contacts)

the attitudes of this formation toward the ends of the cross

section are unknown and have been assumed in their

representation. It is possible that the unconformity between the

Huichica and Great Valley rocks is angular but information to

draw this conclusion is lacking due to the massive nature of both

units.

Associated with the folding are abundant·--;;-:li·c'kel'i;<;ftae-s·--- ~ (sheared surfac-es·-produced by the tight f old~~-9Twn1ch- ;;~-;;-~-r

--- ~

co;;-centrated -in Huichica clays along the overturned limb, that

is, dull scattered slickensides beginning at Sta. 4+40 in Trench

''A'' and becoming pronounced and abundant from Sta. 4+55 to Sta.

4+63 with an occasional dull slickenside noted beyond to Unit 6F.

Abundant gypsum crystals occur within this interval. Numerous

dull slickensides and gypsum crystals occur from Sta. 4+57 to

I Sta. 4+67 in Trench ''B'', within the Huichica in all of Trench

"C'', within the Huichica from Sta. 0+24 to 0+55 in Trench "D",

I and numerous dull slickensides (no gypsum) occur in the Huichica

clays throughout Trench ''E." In all cases the orientation of the

I slickensides is random. In addition, they become more shiny with

I 14


depth due to diminishing weathering.

Photo-Geologic Interpretation

Aerial photographs as listed in Appendix "5" were studied

for lineaments. As shown in Appendix "A," two lineaments have

been added to those previously mapped by Darwin Myers Associates.

one on the easterly slope of Oat Hill and the other on the

subject site. Both of these photo-features are northwest

trending and discontinuous. The lineament on Oat Hill is likely

related to the northwest striking and steeply dipping sediments

of the Unnamed formation while the origin of the lineament on the

subject site is likely associated with the axis of the anticline •

as it is essentially coincident with it. Also, it appears likely

that the low ridge at the northerly end of the property has been

produced by the anticline.

Seismicity

As shown in Figure 9, "Regional Epicentral Map,'' very little

seismic activity has occurred in the general area of the site

since 1969, at which time the u.s.G.S. initiated more thorough

coverage of the area by strong-motion seismographs (Calnet

System) spurred by the Santa Rosa earthquake of that year.

The following is a list of faults which are considered

active and which pose a hazard to the site from a seismic shaking

point of view.

15

I .. 1.!

t.. i'· ;/,l/-'

f '' .. . ) ' .

I I I I I I I

Fault

Green Valley/Cordelia

Healdsburg/Rodgers Creek

Calaveras

Concord

Hayward

Midland

San Andreas

Maacama

Distance to Maximum Credible Site (km) Earthquake (Richter)

10 7

16 7

16 8

18 6-1/2

21 7-1/2

43 7

48 8-1/4

56 7

Based upon the work of Campbell (1981) who analyzed the I horizontal components of 27 near-source world-wide earthquakes

of magnitude 5.0 to 7.7, the maximum credible acceleration that


may be expected at the site is on the order of 0.28g. This

maximum value is likely to be produced by the Green Valley

fault's maximum credible earthquake of M7, based upon distance:

magnitude relationships of active faults within 100 km of the

site.

Geologic Hazards

In addition to the hazard of fault rupture, the following

geologic hazards are discussed below: ground shaking,

liquefaction, differential compaction and subsidence, lurching

and ground-spreading, landsliding, seiches and tsunamis, and

flooding.

Ground Shaking induced by an earthquake is primarily a

function of earthquake magnitude, distance to the fault, and the

physical characteristics of the site.

The site is underlain by competent earth materials of the

Huichica formation and Great Valley sequence. These materials

are estimated to possess a high seismic impedance and therefore

16

I I I I I I I

are not likely to cause amplification of seismic energy.

Liquefaction, a sudden and large decrease of shear strength

due to increased pore water pressure caused by seismic motion, is

not considered to be a significant threat to the site inasmuch as

the earth materials are competent semi-consolidated Huichica

sediments and consolidated Great Valley sequence rock. Ground

water is shallow, approximately 10 feet deep, but is likely

restricted to sand layers/lenses within the Huichica.

Differential Compaction and Subsidence are also considered

to be a low-probability hazard inasmuch as the earth materials

are semi-consolidated to consolidated and are very unlikely to

I experience quick consolidation or differential settlement due to

earthquake vibrations.


Lurching and Ground Spreading are not considered a

significant hazard at the site since these phenomena are

associated with steep slopes and low kinetic viscosity of the

earth materials. The possibility of the occurrence of these two

hazards is considered to be exceedingly low, given the very low

slopes and the competent earth materials.

Landslides are not considered a signif~cant hazard at this

location. No evidence of landsliding has been observed on the

property or adjacent to it. The slopes are low (maximum of 25:1)

except for steep 6 ft.± cuts along the railroad tracks at the

northerly boundary. Given the competency of the earth materials

the hazard of landsliding is considered very low.

Seiches and Tsunamis have been analyzed for the San

Francisco Bay area by the

based upon a 20-foot-high

U.S. Geological Survey. Their study,

runup at Golden Gate, hypothesizes a

minor inundation along the bay side of Mare Island and no

inundation up the Napa River. Given the site's inland location,

its elevation (minimum, el. 26) it is extremely unlikely that it

17

I I I

will experience a tsunami. Since the site is not near a lake the

hazard of a seiche is nil.

Flooding of the site is considered to be a very low I possibility given the site's minimum 26 ft. elevation, relatively

small watershed, and lack of major drainages in the vicinity.


Respectfully submitted,

•

Allen D. Bailey Certified Engineering Geologist No. 762

18


REFERENCES

Bailey, Edgar H. (ed.), "Geology of Northern California," Bulletin 190, California Division of Mines and Geology, 1966, 508 p.

Bailey Scientific, "Geologic Hazards Investigation, Green Island Industrial Park, Napa county, California, Panattoni Development Company," 1989.

Balbi & Chang Associates, ''Geotechnical Investigation Report, Tribotech Access Road, Oat Hill, Vallejo, California,'' 1984.

Balbi & Chang Associates, ''Geotechnical Investigation Study, Proposed Water Storage Tank, Oat Hill, Napa County, California," 1984.

Birkeland, Peter w., "Soils and Geomorphology," Oxford University Press, 1984, p. 365.

Borchardt, R. D., "Studies for Seismic Zonation of the San Francisco Bay Region,'' U.S. Geological Survey Professional Paper 941-A, 1975, p. 102.

Brown, Robert D., Jr., "Faults That Are Historically Active Or That Show Evidence of Geologically Young Surface Displacement, San Francisco Bay Region, A Progress Report: Oct., 1970,'' U.S. Geological Survey, 1970, 1:250,000.

Bryant, William J., "Fault Evaluation Report FER-129,'' California Division of Mines and Geology, 1982. (unpublished)

Campbell, Kenneth w., "Near-Source Attenuation of Peak Horizontal Acceleration," Bulletin of the Seismological Society of America, Vol. 71, No. 6, 1981, pp. 2039-2070.

Cardwell, G. T. 1 "Geology and Ground Water in the Santa Rosa and Petaluma Valley Areas, Sonoma County, California," U.S. Geological Survey Water-Supply Paper 1427, 1958, p. 273.

Darwin Myers Associates, "Geologic and Seismic Hazards Reconnaissance, Napa Airport Study Area, Napa county,'' 1983.

Earthtec, Ltd., ''Preliminary Geotechnical/Geological Study, Struble Industrial Park," Napa county, California, 1989.

Environmental Management and Research, Inc., "Fault Hazard Investigation, Preliminary Soils Data, Green Island Industrial Park, Napa County, California," 1979.

Hart, Earl W. "Fault-Rupture Hazard Zones in California, Special Publication 42 1 " California Division of Mines and Geology, 1980.

19


References (continued)

Helley, E. J. and Herd, D. G., "Map Showing Faults with Quaternary Displacement, Northeastern San Francisco Bay Region, California,'' Miscellaneous Field Studies Map MF-881, U.S. Geological Survey, 1977, 1:125,00.

Jennings, C. w., "Fault Map of California,• California Division of Mines and Geology, 1975, 1:750,000.

"Geologic Map of California," California Division of Mines and Geology, 1977, 1:750,000.

Kleinfelder & Associates, ''Fault Study, Oat Hill Industrial Subdivision- Parcel 2, Napa County, California,• 1983.

Manson, Michael w., "Landslide Hazards in the Cordelia-Vallejo Area, Solano and Napa Counties, California," Landslide Hazard Identification Map No. 13, 1988, 1:24,000.

Napa County Board of Supervisors, ''Seismic Safety Element,'' 1975.

Ritter, J. R., and Dupre, W. R., "Map Showing Areas of Potential Inundation by Tsunamis in the San Francisco Bay Region, California,• U.S. Geological Survey, Miscellaneous Field Studies Map MF-480, 1972, 1:125,000.

Sims, J. D., K. F. Fox, Jr., J. A. Bartow and E. J. Helley, "Preliminary Geologic Map of Solano County and Parts of Napa, Contra Costa, Marin and Yolo Counties, California," U.S. Geological Survey Map MF-484, 1973, 1:62,500.

Thomas D. Hays & Associates, Inc., "Geologic Study, Proposed Warehouse for Illman Jones, Inc., Parcel No. 1 of AP No. 58-030-31, Green Island Road, Napa County, California, 1982.

Wagner, D. L., and E. J. Bortungo, "Geologic Map of the Santa Rosa Quadrangle," California Division of Mines and Geology, 1982, 1:250,000.

Weaver, Charles E., "Geology and Mineral Deposits of an Area North of San Francisco Bay, California,• California Division of Mines and Geology, Bulletin 149, 1949, p. 135, 1:62,500.

20


" ;

L

Ref. Sims, J.D. et al., 1973, ''Preliminary Geologic Map of Solano County and Parts of Napa, Contra Costa, Marin, and Yolo Counties, California," U.S. Geological Survey, Miscellaneous Field Studies Map, MF-484.

BAILEY

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I -- SCIENTIFIC

REGIONAL GEOLOGIC MAP

STRUBLE PROPERTY GREEN ISLAND ROAD

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REGIONAL FAULT MAP

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SPECIAL STUDIES ZONE MAP

S'l'RUBLE PROPERTY GREEN ISLAND ROAD

Project No. 378 Datt!: 8-6-91

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BAILEY e SCIENTIFIC

REGIONAL EPICENTRAL MAP STRUBLE PROPERTY

GREEN ISLAND ROAD

Project No. 3 7 8 Date: 8-6-91

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BAILEY e SCIENTIFIC

GEOLOGIC CROSS-SECTION STRUBLE PROPERTY GREEN ISLAND ROAD

Project No. 3 7 8 Date: 7-26-91

Fi.cure 7


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EXPLANATION

Photointerpretive fault trace (solid where location based upon geomorphic feature, dashed where inferred from tonal change)

Fault Scarp

Channel of Intermittent Stream

...

N PHOTOLINEAMENT MAP

&C.A.1.....1'.: 1 111• 1 /2Ml.

FIGURE 5



APPENDIX "B"

AERIAL PHOTOGRAPHS

The following 9 in. by 9 in. black and white aerial

photographs were supplied by the Napa County Conservation,

Development, and Planning Department for this study.

Photograph No. Date Scale

3575-3-224 6-19-73 l" = 2000'

3575-3-225 6-19-73 l" = 2000'

3575-3-237 6-19-73 l" = 2000'

3575-3-238 6-19-73 l" = 2000'

3575-3-239 6-19-73 l '' = 2000'

3575-3-240 6-19-73 l" = 2000'

The photographs were taken at a time of high-sun angle which

resulted in essentially no shadows.

division of mines and geology -...

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