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HARDDIG·LAWSON ASSOCIATES
GEOLOGIC HAZARDS INVESTIGATION BISHOP RANCH
LOTS 1, 2, 5, AND 6 SAN RAMON VALLEY
CONTRA COSTA COUNTY, CALIFORNIA
HLA Job No. 8294,005.03
A Report Prepared for
Sunset Development Company 1819 Barcelona Street
Livermore, California 94550
by
E. C. Winterhalder, Engineering Geologist - 272
Ronald L. Soroos, Engineering Geologist - 1056
Harding-Lawson Associates
!':
7655 Redwood Boulevard, P.O. Box 578 Novato, California 94947
415/892-0821
May 22, 1980
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INTRODUCTION
This report presents the results of our geologic hazards
investigation for the planned light industrial and residential
development of Lots 1, 2, 5, and 6, Bishop Ranch property, San
Ramon Valley, California. The small scale Geologic Map, Plate 1,
indicates the approximate boundaries of each lot within the
property which is within the level floor of San Ramon Valley.
With the exception of Lot 1, there are presently no specific
development plans for the property. Development will, however,
be typical of that in surrounding areas and will include low-
r ise light industrial, commerical and residential buildings.
There are presently no plans for unusually high-use public
buildings or critical facilities for which the acceptable geo
logic hazards risk would be unusually low.
Previous Work
we previously performed a preliminary geological study of
the entire property, the results of which were presented in our
report dated September 19, 1979. That study was based upon
reports of previous investigators including public agency geol
ogists and Woodward-Lundgren Associates who performed geophysi
cal surveys and test borings but no intensive subsurface explo
ration such as trenching. Our preliminary report summarized the
considerable new geologic information available since the
Woodward-Lundgren report and pointed out remaining areas of
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concern with emphasis on the risk of fault rupture. Subse
quently, we have performed an intensive investigation of Lot 1
and presented the results in our Soil and Geologic Hazards
Investigation report dated January 4, 1980. A copy of that
report is appended. This report, covering Lots 2, 5, and 6, is
based upon all of the earlier information plus new subsurface
geologic data which became available in reports of investiga
tions outside the property subsequent to the preliminary study.
Object and Scope of Work
The Bishop Ranch property is within the special study zone
encompassing the Calaveras and San Ramon Valley faults created
in accordance with the provisions of the Alquist-Priolo Special
Studies Zones Act of 1972. The object of our investigation was
directed towards satisfaction of the requirements of the act.
The primary purpose of the act is to preclude siting of struc
tures for human occupancy on the surface trace of an active
fault. Accordingly, our investigation has been directed pri
marily toward a resolution of the question of whether active
faults exist within the property. Other seismic hazards have
also been evaluated utilizing data developed in the course of
the fault investigation. Our investigation has been performed
within the State guidelines for geologic hazards investigations
involving surface fault rupture.
The scope of our investigation consisted of
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HARDING-LAWSON ASSOCIATES
1. Review of all pertinent geologic reports and other data, including our preliminary report, and new information developed subsequently; a list of references is attached
2. Discussions with Mr. James Baker, Contra Costa County Geologist
3. Interpretation of aerial photographs taken during different seasons
4. Electromagnetic surveys
5. Geologic logging of trenches excavated across aerial photo lineaments and vegetation changes, and across geophysical anomalies
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GENERAL GEOLOGIC SETTING
San Ramon Valley and the paralleling mountain ranges to the
east and west are part of the Coast Ranges geomorphic province
of northern California. The northwest-trending valley and
ranges are typical of that province and reflect the orientation
of the more recently active structure, in this case, the
Calaveras and San Ramon Valley faults which approximately bound
the valley floor.
Plate 1 presents the general geology of the property and
near vicinity and is a modification of the map by Brabb and
others, 1971. As shown, the valley is blanketed by Quaternary
alluvium which overlies bedrock of Pliocene and Miocene age
which is exposed in the nearby low hills and higher ridges.
Bedrock formations within the mapped area consist of the Orinda,
Cierbo sandstone, and Briones sandstone formations, all ranging
in age from middle Miocene through late Pliocene. These rocks
were strongly folded and faulted in at least two episodes during
the late Pliocene and Pleistocene epochs. Uplift which accom
panied these events exposed the rocks to erosion and large
volumes have been stripped away in the carving of San Ramon
Valley.
San Ramon Valley was once more deeply carved by a former
stream which flowed northward out of Livermore Valley. At some
time during the Pleistocene epoch, this drainage became blocked
by uplift north of the site. The flow was reversed and San
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Ramon Valley, together with Livermore Valley, now drain to the
south and east into South San Francisco Bay. In the process,
alluvial sediments accumulated in San Ramon Valley, and near the
site, it ultimately filled with up to approximately 300 feet of
stream deposits. These are underlain by the bedrock formations
exposed on either side of the valley. The uplift may have been
due to fault displacements, to uplift related to the Diablo
antiform or to some combination thereof. In any event, it is
clear that differential movement on the Calaveras and San Ramon
Valley fault zones accompanied by uplift has continued up to the
present. This recent uplift in the vicinity is inferred by the
opposite direction of flow of San Ramon and South San Ramon
Creeks on the west and east sides of the valley, respectively.
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ACTIVE FAULTING
Basis for Special Studies Zone
For various purposes, geologists over the past 50 years have
mapped a number of faults in the area on the basis of strat-
igraphic separation in bedrock, topographic inference, histori-
cal descriptions of surface rupture accompanying earthquakes,
differences in ground-water levels, aerial photo lineaments, and
finally, exposure of fault structures in trenches. All of the
fault lines so mapped which could conceivably indicate
Quaternary age faulting were utilized in the delineation of the
Special Studies Zone. The trenching and other more intensive
investigations required for development in the special studies
zone have resulted in significant modification of earlier
mapping conducted for purposes other than evaluation of geologic
hazards.
Plate 2, a map of the Bishop Ranch and adjacent properties,
shows the inferred faults and lineaments which have been mapped
in that area and have served as a basis for delineation of the r- .. : ~--)pecial dtudies·~one. The map also shows the locations of
trenching performed on Bishop Ranch and adjacent properties,
including that performed for this investigation. The trenching
was performed over several years and individual trenches were
located to intercept aerial photo lineaments, geophysical
anomalies, and fault prolongations. Not all of the trenches are ~
shown, only those which are significant with respect to faults
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which might occur within or could logically project into the
property.
Calaveras Fault
The active Calaveras fault, as approximately located on
Plate 1, generally follows the west edge of the valley floor
except where it cuts across the alluvial fan which has been
deposited by San Ramon and San Catania Creeks. Extensive
trenching in that area has clearly indicated the location of
this major active fault and confirms the evidence presented by
Radbruch (1968) concerning the location of surface rupture on
the Calaveras fault accompanying the 1861 earthquake.
Other locations of the Calaveras fault indicated by dotted
lines within the property on Plate 2 are based on topographic
inference for a northward prolongation of the Calaveras fault
into San Ramon Valley. There are no aerial photo lineaments
within the property parallel to the Calaveras fault zone.
Despite this lack of direct evidence for faulting, exploratory
work has been conducted and it has precluded active faults at
those inferred locations (Harding-Lawson Associates, 1980;
Merrill and Seeley, 1980).
San Ramon Valley Fault
Early evidence for a possible young fault on the east side
of San Ramon Valley included aerial photo lineaments trending
west of north and diagonal to the valley axis, differences in
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ground-water levels which might be due to fault-created aqua
cludes, and possible northwestward prolongation of the active
Pleasanton fault mapped by Radbruch in northern Livermore
Valley. Subsequent trenching outside the property on aerial
photo lineaments has confirmed the presence of young faulting -
near the base of the steeper slopes on the east side of Alcosta
Boulevard. There has been some reinterpretation of the earlier
investigation by Burkland (1973) with regard to the relative age
of faulting indicated by trench exposures. This reinterpreta
tion has not substantially modified the location and direction
of the San Ramon Valley fault although some minor eastward
* adjustment is indicated by presently ongoing work.
*James Baker, personal communication.
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ON-SITE EXPLORATION
General
As mentioned previously, the geology within the site has
been investigated before by surface methods including aerial
photo interpretation and geophysical surveys using shallow seis
mic refraction techniques. Prior subsurface investigation was
limited to scattered test borings and water level measurements
in existing wells. The result of this earlier work was the
designation of a geophysical anomaly zone within Lot 5 more or
less parallel or coinciding with two northwest trending aerial
photo lineaments. These have been explored by electromagnetic
(EM) surveys and by trenching oriented approximately normal to
the lineaments and geophysical anomalies. The locations of the
EM survey lines and trenches are indicated on the Site Plan,
Plate 3. Logs of the trenches are explained on Plate 4 and
presented on Plates 5 through 12. The EM profiles are presented
on Plate 14.
Trenches 1 through 3 were excavated about 10 feet deep
across aerial photo lineaments precisely plotted on the topo
graphic base map with reference to identifiable features such as
roads, farmhouses, and so forth. The different aerial photos
show lineaments at slightly different locations and orienta
tions; consequently, the trenches were extended sufficiently to
cover all of the lineaments.
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Surface examination of the ground surface at the time of
trenching revealed distinct vegetation changes coinciding
closely with the lineament at Trench 1. Vegetation changes at
Trenches 2 and 3 were less distinct and questionable. The vege
tation change at Trench 1 coincided with a distinctive change in
surface soil moisture content; higher moisture content being
associated with darker toned areas as viewed on the photos.
Trench Results
Trench 1 encountered moderately plastic clay surface soils
with lower moisture content in the lighter toned area northeast
of the lineament and highly plastic wet clay soils in the darker
toned area southwest of the lineament. The distinct change in
plasticity is confirmed by laboratory tests on two composite
samples; the plasticity test results are presented on Plate 13.
As indicated by the topographic contours on Plate 3, the
lineaments and darker toned soil zone approximately coincide
with a northwest trending topographic low or broad channel which
descends southeastward from near the head of an alluvial fan
generated by San Ramon and San Catanio Creeks. Probably, the
more plastic clays represent gradual filling of a broad,
channel-like depression in the fan following its active develop
ment.
As indicated by the log of Trench 1 on Plates 5 and 6, the
plastic clay surface soils are underlain by interlayered clayey,
silty, and sandy alluvium. With regard to the presence or
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absence of young faulting, the relatively thin but continuous
sand layers penetrated near the bottom of the trench provided
the best opportunity to detect even small fault offsets.
Trench 2 (Plates 7 and 8) which explored the southwest limit
of the darker toned zone, encountered generally similar condi
tions but with no distinct change in surface soil plasticity or
moisture content. Trench 3 (Plates 9 and 10) explored a dis
tinct narrow lineament oriented slightly divergent from the crop
rows visible on aerial photos. Trench 4 (Plates 11 and 12)
explored the seismic refraction anomaly. All of the trenches
encountered similar interlayered clays, silts, and sands which
apparently were all deposited in the aforementioned alluvial fan.
Age of Alluvium
The alluvial soils do not contain sufficient carbonaceous or
other materials which would permit reliable absolute dating by
radioisotope methods. However, the age of the alluvium pene
trated by the trenches can be estimated through correlation of
regional geomorphic events with the depositional environment
indicated by the various alluvial and soil types exposed in the
trenches. Merrill and Seeley (1980) citing Schlemon (1979),
developed a stratigraphic column for the upper alluvium exposed
in trenches immediately north of Lot 2. They point out a
paleosol immediately underlying younger alluvial fan deposits
and estimate its age in the range of 8,000 to 12,000 years. A
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similar dark brown paleosol was encountered beneath sandy
alluvial fan deposits in the trenches for Lot 1 (see appended
report). Trench 3 for the present investigation also encoun
tered a dark brown clay with a mottled and fissured texture
typical of paleosols beneath alluvial fan deposits at a depth of ,,
about eight feet. On this basis, it can reasonably be concluded
that all of the alluvial fan deposits penetrated by the trenches
within the property and adjoining areas are of a similar age.
Detailed logging, as indicated on the trench profiles, dis
closed no abrupt discontinuities in the alluvium which would be
attributable to faulting. All irregularities within the
alluvium are of a type most reasonably attributable to the ordi
nary fluvial processes.
Electromagnetic Surveys
Prior to trenching within Lot 5, we performed four electro
magnetic profiles at the locations indicated on Plate 3. Their
purpose was to measure the electrical conductivity of near
surface alluvium as an indication of anomalous discontinuities
which might then be explored by trenching. The surveys were
performed on December 4, 1979, by our geophysicist using a
Geonics Model EM-31 electromagnetic induction system. This
equipment incorporates a fixed coil spacing of 12 feet and
generates an alternating magnetic dipole field which induces a
current in the ground penetrating to depths of 15 to 20 feet.
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The equipment then measures the secondary magnetic field which
is set up by the current in the ground. The instrument provides
direct readout of the measured conductivity of the soil in
millimhos per meter. The profiles are plotted on Plate 14.
Profiles 1 and 2 detected no significant anomalies. The
minor fluctuations are due to soil grain size and moisture con
tent variations as revealed by the trenching within Lot 1 and
the trenching performed by others in the adjacent property to
the north. EM Profile Line 3 crossed the aerial photo lineament
near Trench 3 and the ranch road separating plowed ground on the
east from orchard on the west. A persistent change in conduc
tivity was noted at the roadway with higher readings in the
plowed ground and lower in the orchard. Repeated profiles
across the road at nearby locations disclosed the same change.
No variation or anomaly was noted at the lineament between this
road and the railway. We concluded that the conductivity change
is due to higher near-surface moisture in the plowed ground than
in the orchard.
EM Line 4 was performed in the area of Trenches 1 and 2 and
crossed several aerial photo lineaments. This line detected the
greatest anomaly of the four lines. A distinctively higher con
ductivity was encountered in the vicinity of the darker toned
soils and it coincided approximately with the more plastic soils
with higher moisture content encountered in Trench 1. A similar
increase in conductivity coincides with the lineament crossed by
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Trench 2. We believe the anomalous conductivity measured by
Line 4 is probably due to near-surface variations in soil mois
ture content as indicated by the trenches. The EM survey
results are believed to be supportive of the other data indicat
ing local variations in surface soil conditions and an absence
of anomalous discontinuities in the upper 15 to 20 feet of
alluvium.
Off-Site Trenching
In addition to the trenches within Lots 1 and 5, extensive
trenching has been performed near the north property line by
Peter Kaldveer (1978 and 1979) and by Merrill and Seeley
(1980). These trench locations are shown on Plate 2. They pro
vide an essentially continuous profile through the upper
alluvium across the northerly end of the property. Merrill and
Seeley state that, "Based on our evaluation of previously exist
ing information and subsurface data developed specifically for
this investigation, we have concluded that the subject property
is free from evidence of active faulting. It is our opinion
that the potential for future surface faulting is low and that
the property can be developed with noncritical structures for
human occupancy". This statement is in regard to the entire
property adjacent to the north boundary of Lots 1 and 2.
Together with the trenching performed in Lot 1, the investiga
tions effectively I:i::eslude active fau},ts within the property
parallel to the Calaveras fault and any northwest striking
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faults which might extend through the northeast portion of the
property from the San Ramon Valley fault.
One other northwest striking aerial photo lineament has been
mapped near the southwest corner of the property (Lot 6) as
indicated on Plate 2. Exploratory work was performed in that
area by United Soil Engineering, Incorporated (USE!) in reports
to Shapell Industries, developers of a subdivision property
immediately south of Lot 6. The investigation included exten
sive trenching along Ascot Drive extending approximately the
full width of Lot 6. It revealed no indications of faulting.
On this basis, we conclude that the aerial photo lineament in
that area is due to processes other than faulting and probably
is related to near-surface soil conditions as disclosed in our
trenches within the Bishop Ranch property. On the basis of the
USE! investigation, the subdivision was granted approval in
compliance with the requirements of the Alquist-Priolo Act.
To the east, Berlogar, Long & Associates (1978 and 1979) and
Berklund & Associates (1973) performed numerous trenches to
evaluate the San Ramon Valley fault zone, as inferred by aerial
photo lineaments. The results of their trenching indicate that
Holocene or post-alluvium faulting has occurred in an irregular
zone approximately indicated by the fault traces on Plate 1.
Trenches adjacent to the east side of Lot 5, as shown on
Plate 2, revealed no indications of faulting that would project
northwestward into Lot 5 or Lot 2.
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SEISMICITY
Plate 15 presents, on a regional scale, the major known
active faults within the San Francisco Bay Region and the loca
tions of epicenters for earthquakes greater than magnitude 4
during the period from 1934 through 1976. As shown, the site
lies a short distance east of the Calaveras fault and within
about 15 and 45 kilometers, respectively, of the Hayward and
main San Andreas faults farther to the west. As shown, there
have been a number of historical earthquakes in the range of
magnitude 4 to 6 centered near the Calaveras fault. Nearly all
have occurred in the area to the south of San Jose and none
within the immediate vicinity of the site.
The more notable earthquakes in the Bay Region occurred
prior to 1934, including two major earthquakes on the Hayward
fault in 1836 and 1868, and the great earthquake of April 18,
1906, on the San Andreas fault. The star symbol on Plate 15
indicates the focal center for this event although it preceded
1934. Early records describe an earthquake on the Calaveras
fault in 1861. Due to lack of instrumental records and the
remote location relative to population centers at that time, the
event is poorly documented. However, based on reported inten
sities, it has been assigned a magnitude of about 6. Surface
rupture was reported in two areas, one a short distance north
west of San Ramon Village. The location, if correct, coincides
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closely with the presently located surface trace of the
Calaveras fault.
There have been no significantly damaging earthquakes on the
San Ramon Valley {Pleasanton) fault during historical time. Lee
and others, 1971, suggest the possibility that a sequence of
small earthquakes which occurred near Danville in 1970 may have
been caused by movement on a possible northward continuation of
the Pleasanton fault. At that time, the Pleasanton fault had
been mapped only in the vicinity of Pleasanton in Livermore
Valley; there was no mapped northward continuation to the vicin
ity of the earthquake sequence. Present mapping of the fault
suggests it could have been responsible for the sequence
assuming that it has an eastward dip. This is consistent with
the eastward dip generally observed in the trenching at nearby
sites.
In summary, the historical earthquake records indicate a
potential for strong earthquake shaking at the site with maximum
magnitudes in the range of 6 to possibly 7 for local events on
the Calaveras fault, about 7 on the Hayward fault, and up to
8-1/4 on the San Andreas fault. Judging by the historical
record and considering the length of the San Ramon Valley -
Pleasanton fault, it would appear that its magnitude potential
is low in comparison to the other faults mentioned. Conse
quently, even though this fault is quite close to the site, the
Calaveras fault possesses the greater potential for damaging
earthquakes.
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CONCLUSIONS AND RECOMMENDATIONS
Surface Rupture
Based on our investigation, we conclude that there are no
indications of active faults within the property. All of the
surface indications of faulting or inferred faults have been
shown not to exist or to be due to geological processes other
than faulting. Furthermore, there are no known active faults
which would logically project or propagate into the property
from outside.
Geologically young active faults are known to exist outside
the property both to the west and east. Old faults no longer
active undoubtedly exist in the bedrock nearby and beneath the
site. Conceivably, new displacements on the nearby active
faults might also be accompanied by small displacements on those
old faults beneath the site. However, it is generally agreed
that, from a probability standpoint, any significant new fault
displacements within the relatively brief span of 50 to 100
years would be far more likely to occur on known active faults
which have experienced repeated displacements in most recent
geologic time. Consequently, we conclude that the risk of ~.
on-site surface rupture is small and can be safely disregarded i in the siting of buildings as presently planned for the property. l
i Because of the inherent limitations in the evaluation of th~-·~
future behavior of geologic phenomena, we cannot preclude all
possibility of future faulting. This would be true for any
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seismically active region where faulting has occurred at various
times in the geologic past. This inherent uncertainty has been
incorporated in the concept of balanced acceptable risk adopted
by the State of California. This concept recognizes that
various types of building usage or activities involve widely
varying degrees of risk to occupants from seismic activity,
including faulting. The consequences of damage to a light one
or two-story residential structure are potentially much less
severe than damage to a hospital, for example. Critical struc-
tures such as large dams and nuclear power plants, if damaged,
represent a significant hazard well away from the structure
itself. For such structures, a highly intensive and often
costly investigation of seismic hazards is warranted.
Applying the concept of balanced acceptable risk to this
proposed development, we believe that the level of investigation
which has been accomplished is appropriate and sufficient with
regard to our present understanding of geologic structures in
the region. Supplemental investigation of seismic risks may . .,- .... ,_.,,,.-- .. ' ,. -·
become appropriate in the future for particular building types
or site usage. That decision must unavoidably be made when.-··i:.he
specific usage is proposed and in the light of any new geologi
cal information which may be significant to that particular
site. Such supplemental investigations might include further
evaluation of faulting but more probably would be directed
toward the earthquake shaking risk and response of the site and
building to strong earthquake shaking.
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Foundation Conditions
With regard to the general foundation conditions, probably
of greatest significance from a design planning and development
cost standpoint are the presence of expansive surface soils and
near-surface compressible alluvium. Plastic and expansive sur
face clays are widespread although as we have seen, they are not
everywhere highly expansive. Our previous investigation of
foundation conditions within Lot 2 indicates no unusual founda
tion problems from the standpoint of soil compressibility and/or
adverse response to earthquake shaking such as liquefaction and
densification. The requirement for modified foundations such as
piers to gain support below the zone subject to expansion or
consolidation should be based upon detailed investigation of the
conditions at specific building sites. Large or heavy struc
tures with high foundation loadings should be the subject of a
thorough soil investigation, possibly including site response
analysis where the structure, soil and ground-water conditions
so indicate.
Earthquake Resistant Design
Regardless of the particular site conditions, all structures
should be designed to resist strong earthquake shaking even
though no active faults have been found to exist within the
property. The close proximity of two active faults, in particu
lar the Calaveras fault, indicates the need for careful atten
tion to earthquake resistant design. Based on the earthquake
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history, at least one strong earthquake can be expected to
affect the site within the average building lifetime. The
earthquake, or earthquakes, could either be local events with
moderate magnitude and moderate to high intensity or they could
be from relatively distant sources such as the San Andreas
fault, but still with high intensity at the site. Development
of a design earthquake should consider the earthquake history of
the region as indicated on Plate 15.
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PLATES
Plate 1 Geologic Map
Plate 2 Inferred Fault, Lineament and Trench Location Map
Plate 3 Site Plan
Plate 4 Explanation of Trench Logs
Plates 5 through 12 Trench Logs
Plate 13 Plasticity Chart
Plate 14 Electromagnetic Profiles
Plate 15 Active Faults and Earthquake
DISTRIBUTION
6 copies: Sunset Development Company 1819 Barcelona Street Livermore, California 94550
Attention: Mr. M. R. Mehran
ECW/RLS/jd
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Epicenters
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REFERENCES
1. Berlogar, Long & Associates, August 1978, Supplemental Investigation II, Vista San Ramon Subdivision 5204, San Ramon, California.
2. Berlogar, Long & Associates, November 1979, Geotechnical Investigation, Proposed Church Facilities, Alcosta Boulevard, San Ramon, California.
3. Bolt, B. A., and R. D. Miller, 1975, Catalogue of Earthquakes in Northern California and Adjoining Areas, 1 January 1910 - 31 December 1972, Seismographic Stations, University of California at Berkeley.
4. Borcherdt, R. D., 1975, Studies for Seismic Zonation of the San Francisco Bay Region, U.S. Geological Survey Professional Paper 941-A.
5. Brabb, E. E.; H. s. Soneman; and J. R. Switzer, Jr., 1971, Preliminary Geologic Map of the Mount Diablo-Byron Area, Contra Costa, Alameda and San Joaquin Counties, California, U.S. Geological Survey, Basic Data Contribution No. 28.
6. Brown, R. D., Jr., and w. H. K. Lee, 1971, Active Faults and Preliminary Earthquake Epicenters, 1969 through 1970, in the Southern Part of the San Francisco Bay Region, USGS Miscellaneous Field Studies Map MF-301.
7. Burkland and Associates, November 1973, Geologic and Seismic Hazards Investigation, Winston Valley, Contra Costa County, California.
8. California Department of Water Resources, 1964, Crustal Strain and Fault Movement Investigation, Bulletin 116-2.
9. California Department of Water Resources, 1966, Evaluation of Ground Water Resources, Livermore and Sunol Valleys, Bulletin 118-2, Appendix A.
10. California Department of Water Resources, August 1967, Evaluation of Ground water Resources, South Bay, Appendix A: Geology, Bulletin 118-1.
11. California Division of Mines and Geology, 1961, Geologic Map of California, San Jose Sheet.
12. California Division of Mines and Geology, 1972, Preliminary Earthquake Epicenter Map of California, 1934-1971 (June 30) , Seismic Safety Information 72-3.
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13. Ford, Robert S., October 4, 1969, Ground-Water Geology of Livermore Valley - A Satellite Urban Area, in Urban Environmental Geology in the San Francisco Bay Region, Association of Engineering Geologists, Special Publication.
14. Gibson, w. M., and H. A. Wollenberg, 1968, Investigations for Ground Stability in the Vicinity of the Calaveras Fault, Livermore and Amador Valleys, Alameda County, California, Geological Society of America, Volume 79, pp. 627-638.
15. Harding-Lawson Associates, November 11, 1971, Seismic Risk Assessment, The Bishop Ranch Property, Contra Costa County, California.
16. Harding-Lawson Associates, October 22, 1973, Preliminary Soil and Geologic Investigation, Planned Danville Country Club, Danville, California.
17. Harding-Lawson Associates, September 19, 1979, Preliminary Geological Study, Bishop Ranch Property, San Ramon Valley, Contra Costa County, California.
18. Harding-Lawson Associates, November 10, 1979, Preliminary Soil Investigation, Bishop Ranch Lot 2, San Ramon, Contra Costa County, California.
19. Jennings, Charles w., 1975, Fault Map of California with Location of Volcanoes, Thermal Springs and Thermal Wells, California Division of Mines and Geology, California Data Map Series, Map No. 1.
20. Peter Kaldveer & Associates, September 1979, Fault Location Study, Proposed Commercial Development for Frank Henry Associates, San Ramon, California.
21. Peter Kaldveer & Associates, 1979, Geotechnical Investigation, Wells Fargo Bank, San Ramon, California.
22. Peter Kaldveer & Associates, October 1979, Fault Location Study, Proposed 13.25-acre Commercial Subdivision, San Ramon, California.
23. Lawson, Andrew C., 1908, The California Earthquake of April 18, 1906, Report of the State Earthquake Investigation Commission, in two volumes and atlas: Carnegie Inst. Washington, Publication 87.
24
I I I I I I I I I I I I I I I I I I I
HARDING-LAWSON ASSOCIATES
24. Lee, w. H. K.; M. s. Eaton; and E. E. Brabb, 1971, The Earthquake Sequence Near Danville, California, 1970, Bulletin of the Seismological Society of America, Vol. 61, No. 6, pp. 1771-1794.
25. Radbruch, D. H., 1968, New Evidence of Historic Fault Activity in Alameda, Contra Costa, and Santa Clara Counties, California, Proceedings of Conference on Geologic Problems of San Andreas Fault System.
26. Saul, Richard B., March 1967, The Calaveras Fault Zone in Contra Costa County, California, California Division of Mines and Geology, Mineral Information Service, Vol. 20, No. 3,
27. Schlemon, J., 1979, Late Quaternary Soil Stratigraphy, General Electric Reactor Site, in ESA Geologic Investigations Phase II, GE Test Reactor Site, Appendix A, unpublished consultant's report.
28. Seismological Society of America, Bulletin, Volume 60, No. 6, December 1979, pp. 2094-2096 (Danville Earthquake).
29. Townley, Sidney D., and Maxwell w. Allen, January 1939, Descriptive Catalogue of Earthquakes of the Pacific Coast of the United States 1769 to 1928, Bulletin of the Seismological Society of America, Volume 29, No. 1.
30. United Soil Engineers, February 1976, Geologic and Geophysical Investigation, 120-acre parcel, Shapell Industries, Inc., San Ramon, California.
31. Woodward-Lundgren & Associates, October 1972, Active Fault Investigation and Preliminary Soil Investigation, Bishop Ranch, Contra Costa County, California.
32. Woodward-Lundgren & Associates, 1973, Environmental Geotechnical Input, Contra Costa County Assessment District 1973-3, San Ramon, California.
Aerial Photographs
AV-1056-020-5 to 07 AV-334-21-23 to 26 AV-353-23-32 to 39
5/24/72 7/2/59
5/23/57
25
1:12,000 1:8,500 1:12,000
I I
- I .
I I I I
: _, I ,• .
I / .. I -_ ___ . To
I EXPLANATION
I _,..._.. FouN -•• •
I Note' totodified Ir- 8ral>ll, elal, 1971.
.!&
°"""'-' "'-
-HAl'llDINO ·LAWSON ASSOCIAT•S
Couulting Engineers and Geologi•t•
Appr· t:;i:."'-' Date 5/22/80
:D:tot ll!lL. Qal
To
Tc Tb
...,
< ~ ! < ' ~
J.. ...
Scale• I in.=2000ft ~ FQ!!totAT!QH
lJnconlOftdatrrld Olknium, Clar', litt,sond,ond QrOVei st'90fft ........ .
Ortnda bfl'ldont l'IOft-marine mudltone, sdt;one, wdslu a -and C011tiqloi•• all. Cierto ................... ..
._ - bnoliun.
PL ATE GEOLOGIC MAP
Bishop Ranch Contra Costa County,Califo~nia 1
I I I I I I I I I I ~· ... ~·
I I
•' ,/"
./ . - , ·-I \. _____ ----r---• - 1 _
'
/i ~--
I /
I --·1 . -· E
I -,_.,_ __ _
~ . -" . -~--
I
I I I
' . . ~ ·--~.;:...-~, .. i£.~_:~:~-~-::: .~ :1,};.;:~~~~..:.r"'"""~--~•~i'6~i~,:.a- ;~" '· .,,, __ . :..:.;.;.;;;'~'.J:.';>~'.i-,;; .;,_,_:~.11~~1~-v-~~:_j..:..c.. __ ::,:~-~~~.:'t~~~,~~~8~i~:i~~~- ,,;;0;.~!;'.!!<!lv"it'-'i"c',1.bi,.,,;,u± . .:.;.:~ ~- -, .
Trench, lot and trench number in box
EXPLANATION
t-- EM ---l
r17f--
© ' j.-·
Electromagnetic induction profile
Aerial photo lineament
~
~ -·
r
! _)
I. ./
J
.... I
~ --------1--
·1 i !-i I
L
1
-~_j __ \ ..
\ -~L__
.................. ~ ,_ IO A••eOIAT••
lf•--G ... _
/
I 111'
~
'"""""'"'""'"'' 'm•• ''T> ,.,,..,, ,.,.,. • ..,.,.
j
'"" 3
I I I I I I I I I I I I I I
• ITTTIT:m llllilill
". "o •••• • 0 •
: o'· . . . . a .. Cl.. rl 0
EXPLANATION
Dark brown clay, high plasticity, organic surface soils
Dark brown clay, medium plasticity, silty, organic surface soils
Brown to light brown, silty clay to clayey silt, mottled and fissured with abundant fine root holes, abundant mottled light gray carbonate nodules and stringers
Brown to light brown sandy silt to sandy clay, with abundant mottled light gray carbonate nodules and stringers, abundant fine root holes
Brown silty to clean poorly graded sand, fine to coarse-grained
Brown sandy gravel to gravelly sand
HARDING• LAWSON ASSOCIATES Engineers 1 Geologists and Geopflys/Cists
5 22 80 Approved Date
EXPLANATION OF TRENCH LOGS
Bishop Ranch Contra Costa County, California
PL ATE
4
lr-~~~~~~~~~~~~~~-~-~~---==~--=---------------------·~~=-..::~-=-----"------'c_---__,·· u.
1°'
I I I I I I I I I I
\I I
465
15 460 H
It ~ w
455
465
... "' es 460 H
:;: ~ w
455
0 10 20 30 40 50 60 70
I I I
~JLLLL.._ ____________ 11~·1:! ffillTTT'" __________ :!:i./J.L,_,__ _________ 11m ITTiTITi I' 11i!i'1·1: I. : I
'1' : I I ' 'I I I ! ; 1 I I
! .. ! .1 i I
H+i-l-µ_J..U..µ.u.J../..J..U.J..J.JJ..J... ___ ---- ----------------------====:·3"::;::::=:::=:::=======~~~
4/29/80 4/29/80
70 80 90 100 110 120 130 140
~ '
0 5 lOft. See Explanation, Plate 4 Continued on Plate 6
HARDING• LAWSON ASSOCIATES
~ Consulting Engineers and Geologists
Job No .. ==8=2=9=4'::, o=o=5='.=0-=-3 __ Appr· t".'Zt-voate 5/22/80
LOG OF TRENCH 1 SHEET 1 of 2
Bishop Ranch Contra Costa County, California
PLATE
5
r--N.....LL
I I I I I I I I I I I
465
.µ .... 460
z 0 H
~ ~ "' 455
I
,J 465
.µ 44 460
15 H
;;: ~ "' 455
450
~ Continued from Plate 5
iff{n+{..P...,.------- - - -----------------------
.. : ... ·. ·. · ... ~·-· .··.::
r- ~--- ---,-140 150 160 170 180 190
l+A+H~'~-------------- ------------------- ------- --- - ---- -------
,-----------~-----------~ I --···--- --1
200 210 220 230 240 250
0 5 lOft.
HARDING - LAWSON ASSOCIATES
~ Consulting Engineers and Geologists
Job No. 8294, 005. 03 Appr· &k)Date 5/22/80
200
LOG OF TRENCH 1 SHEET 2 of 2
Bishop Ranch Contra Costa County, Cal i:·)rnia
PL ATE
6
~r----------------.-----------------------=~ .;_I----------------------------. 1
I I I I I I I I I I I
460
455 .µ 4-<
15 H
!;: :> ;s 450
"'
445
r~----------------_--------------------~-------~~ I,
11 I' I I! , : Ii ·::::: l ~------------------------------- - - ------------~·111:~:m1:1::1: 1 : ~:n1 • • • . ,. 1· • , •. .i
• • 1· ' 1' • I ....•. 1.:
... . · .. : .. : : . . . . . . : .
0 5 !Oft.
f
f i
Continued or. Plate 8
See Explanation, Plate 4 HARDING - LAWSON ASSOCIATES
~ Consulting Engineers and Geologists
LOG OF TRENCH 2 SHEET l of 2
Bishop Ranch
PL ATE
7 Job No. __ 8_29=4='=0=0=5=·=0=3==A~pp!::r'.;;::;:P:C='.::::b::::!-:'.a!'.te:.:;:;5;;:/=22:/=8:0::.JL_c_o_n_t_r_a_c_o_s_t_a_c_o_u_n_t_y_,_c_a_l_i_f_'.)_rc-'i_· a_..J ___ _J
-c-- -------------- ----------- -----------
' I I I I
I
I I
Continued from Plate 7
.., ""' ~ H E-< .0: :> el r.l
.., ""' z 0 H
~ el r.l
460
455
450
445
460
455
450
445
.... .... ... r::.: . : .. : . '"".. .. I . . . • .......
...
70
----------------------------..
' .. •I•'• ' • . ... ·. . ..
80 90 100 110 115
r 1t+f-------------______________ ...J......., ........ ~...l,-j
-----------------------------lY+H-t Ii: . ' : . : . .... r ..... ". r ..... · .. 1· ...... .
:::. : : : : : : : : . ,_ .......... :: .. r ... I·• • ..
. ..
115 120
0 5 !Oft.
130 140 150
HARDING• LAWSON ASSOCIATES
~ Consulting Engineers and Geologists
Job No. 8294,005.03 Appr:EZWoate s;22;00
160
LOG OF TRENCH 2 SHEET 2 of 2
Bishop Ranch Contra Costa County, California
PL ATE
8
------------ ---------------------- --- --------------- -------- --- --------- ------------------------------------------------------ ------------- ---
IN--~~~~~~~~~~~~~~~~~~~~~~~~~~~---~~~~~~~-, II.
"' I I I I I I I I I I I
445
. 440 +-' ....
5 ,., ~ :> "1 ..< 435 "1
4/29/80
430
0
I I
__,..,.--------=::....-::.-:==..::-::.=---=--.--------- - ---- - - ----- .d I
10 20
0
See Explanation, Plate 4
. . . •' • ·:~ • .., 0
\------~------,-~-:--:--::--:--::--;,---:-::'::::;: . : .•• : ••• :·. . . ". 0. 0 • ()
4/29/80 ~ " 'o • • o · 'o • · 'o. r:> o ' " · · 0 ', o • " · :;;-.:..: · • • '""·'· " ·
'O,p,.O.C,O
. · .... · . . . . .
30 40 50
5 lOft.
HARDING - LAWSON ASSOCIATES
~ Consulting Engineers and Geologists
i-'t:1. o · . .-......:.. . : : ·I
0 •• ·o: o; o ." ;;:--:::1
60
Continued on Plate 10
LOG OF TRENCH 3 SHEET 1 of 2
Bishop Ranch
PL ATE
9 Job No. 8294,005.03 Appr:e&...)oate 5122180 Contra Costa County, California
l--------u.
f I I I I I I
Continued fran Plate 9
. .µ ....
~ .... ;;: &i ..:!
"'
.µ
"' z 0 .... ;;: :>-~ "'
445
440
435
60
445
440
435 f• .......... .
105 110
0
r==r:r:=7·" • ... I ••
70 80 90 100
120 1°30 140
5 !Oft.
HARDING - LAWSON ASSOCIATES
~ Consulting Engineers and Geologists
Job No._s_2_9_4_, _oo_s_._o_3 __ Appr:tu.J Date s;22;so
105
150
LOG OF TRENCH 3
SHEET 2 of 2
Bishop Ranch Contra Costa County, Califor~ia
PLATE
10
~ -~-------------( ,...-------------=-----_---=----_--_---=--------_---=------_-----_---_-----_----_--------_--_---=-----_-_----_-_ ____,---
' I I I I I I I I
..., "' ~ H 8 ..; :> ~ .., ~
445
440
435
445
435
0 10 20
50 60 70
See Explanation, Plate 4
30 40
80 90
0 5 lOft.
HARDING• LAWSON ASSOCIATES
'9 Consulting Engineers and Geologists
Job No .. _8_2_9_4...:.,_o_o_s::.... o:..:3:___Appr: &,,Joate s;22/80
50
100
Continued on Plate 12
LOG OF TRENCH 4 SHEET l of 2
Bishop Ranch Contra Costa County, California
PL ATE
11
11..---------_----_---_-_----~-=-=------=._---~--_--_--~-----_--_------=-=--::-_---_---_-----_----_--_----_----_----_--_--_--_----_----_--_______ ---_-----_--_---_--_-----_---_---_---_--_-_----___ ----u.
1t Continued from Plate 11
II 445
., 4-<
rl z 0 H E-o 440 II ~ f'.l Ol II
435
I I I
445
., 4-<
1§ H 440
~ Ol >-1 Ol
435
l fn-p-·~~ ~==--==------rri1··· .. :~_-_=--:=_--_--__ -=--_--_--_-___ - __ =:-___ I_,,,~.. . .·;
1:·?· ..•. ,[__ - ---- I h·~;_;..,:,,. '--..---- --.----- ------- I .......... . £· c ~ . . . . • ------- --~ -- --~.-±:~::!= ..... •:·'. ·:,.· o.o, o·o· o .. : : .· : .. . . . .. ::;,...;..-~. o I
100
. . . . . . . ~-..:...!~'LL. 0 • "1 ·:· .. ·.. ' --,
110 120 130 140
I I I I
150
M,:...~-----------------------... r--·---------------j_ ·.·.· .. --------------ii· .. ,,......------ i --'Tf
I. . . w------------'Tlll· .. • ·w--------=:::.::::.===- -----t--.,,.-M .. +I ttli~ I' '1
1 I' ________ l ___ ... W#".'
--- ---- I . --=---- -- - - ---------- - L.J...l..'-''----. -.-. . . ------ ~ l·o· D· • , 0
• • ',a· o: •. ~ • 0 0: 0 ~"j·jj;:;:::":.I..~~;:is..,,...-10· •• o.' .· .. . o. -.-... .---_.,------ . ''o;,....~·.:··-·· -------..:.. • 0 • • • • • • •• • --~;,..;"" ••• •• 1. . • ----=- 0 ...... ~·~·'"""~·_,_~· ..... ______ :::.::._ ...... _.;'-'""..-
1. • • --=-..:..-.. 1 .. I . : : I,' .
150 160 170 180 190
0 5 lOft.
HARDING- LAWSON ASSOCIATES
~ Consulting Engineers and Geologists
Job No. 8294, 005. 03 Appr:&woate 5/22/80
200 205
LOG OF TRENCH 4 SHEET 2 of 2
Bishop Ranch Contra Costa County, California
PLATE
12
70
60
~ so t. x w Cl 40 z ~ 30 Ci i== "" ~ 20
CH / /
/ CL .A. /
/
/ A Line v I
"-
10
0
CL - MLJ v MH or OH
ML - CL, /
~v ML or OL M I I . I .
0 10 20 30 40 so 60 70 80 90 100
LIQUID LIMIT(%)
Symbol Classification and Source liquid Plastic Plasticity % Passing
• DARK BROWN SILTY CLAY (CL) (northeast of lineament)
DARK BROWN SILTY CLAY (CH) (southwest of lineament)
HARDING - LAWSON ASSOCIATES
@ Consulting Engineers and Geologists
ob No. 8294 005 03 Appr: e?-t...l Date 5/22/SO
%
41 22 19
56 21 35
PLASTICITY CHART
Surface Soils - Trench 1 Bishop Ranch, Lots 1, 2, 5 and 6
112
PLATE
13
1-II. IX
I I I I I I I ii I 11
I
I I I I
----- - - ------ -
--40
--30
w --20
~ - 40
- .... 30
w - - 20
--50
--40
NE
--30
-- 50
- 40
·- 30 NE
- - 20
E Trench
/'- E . / '· - . '· ·-· \ ·-· ./ '----·" ........ -· ...... / \ LINE 2 ·-· / \ / ., . .-·-·-·.... _,.--/ . ....,
\. ./ \/ \. ,,./ ....... / ........ __ ................. ___ ./ ' / ....... ____ ....... . ........ " __ / ·-·-· ' ' ,, ' / _, \ . ..-./ -·,./ ...... _.-·-·
- Plowed Road Orchard-
t .......... /'-. / ..... /'\ ...... . ·-..... -, . ......__/ __ ,,,,..,_
I ·-· \ , '·-- .... . / -·\ LINE 3
\ ---·-· '·-·-·, .... ........ ./·-... ...... _ , ___ ..... -- . ............. ,,,--......... ___ ./ SW
Powerlii!.es
/., ..... '-...,,.._,
. ·--...'-/ ·-,
/. '·, . \ /-·,_
I . , /. \ . ' /'- . SW ~ '·-·-·-·-· ·-· ' ........ .-· "----· .,
-_____ _,,... . .._,, .......... --·-·-·..... w t z . ,,.
-- .-- e one '---·----· LINE 4
0 . 200ft. 400ft. .
' Horizontal Scale
HARDING - LAWSON ASSOCIATES
~ Consulting Engineers and Geologists
ELECTROMAGNETIC PROFILES
Bishop Ranch San Ramon
Contra costa,County, California
'
PLATE
) ~- ~r-
--~ d"~"""' ·~.,- ,, "'--+~ _''i:'.
I )
Reference: ..:al1fornia Division of ~incs & Geology, 1975, Fault Map of California, and Bolt ~hllcr, 19"75, Catalogue -,f f:arthqu:.lkes in ~ortri.ern
\ .. ll1fornia, updated in June i'):'i, by R. Uhrhammer.
o~~,,;;IOiioiiiiiii2iii0~~~30ii;;;;;;_4_0~~"50 Km.
O 10 20 30 40 Miles ~~~~~"!""'5iiiiiiiiiiiiiiiiiiiii
HARDING - LAWSON ASSOCIATES
Cons11lting F .. :ngi1ictrs nnd Geologists
ob No 8294,oos.~ __ Apprc.c:<J Date s;22;so
EXPLANATION
EARTHQUAKE EPICENTERS '
SYMBOL MJlGNITUDE
0 4.0 -4.4 '" © 6 ~
0 0 t?
<~ -.:._"'"
ACTIVE FAULTS 13 EARTHQUAKE
EPIC ENTERS, SAN FRANCISCO
BAY REGION 1934-1976
PLATE
15
I I I I I I I I I I I I I I I I I I I
Appendix
SOIL AND GEOLOGIC HAZARDS INVESTIGATION BISHOP RANCH BUSINESS PARK, LOT 1
I I I I I I I I I I I I I I I I I I I
HAl:'DING·LAWSON ASSOCIAT£S
SOIL AND GEOLOGIC HAZARDS INVESTIGATION BISHOP RANCH BUSINESS PARK, LOT 1
SAN RAMON, CALIFORNIA
HLA Job No. 8294,004.03
A Report Prepared for
Sunset Development Company 1819 Barcelona Street
Livermore, California 94550
by
E. C. Winterhalder, Engineering Geologist - 272
tJe41B. wtnnfl ~l'~ Cecil B. Wood,
Civil Engineer - 18671
Harding-Lawson Associates 2430 Stanwell Drive, Suite 110
Concord, California 94520 415/687-9660
January 4, 1980
I I I I I I I I I I I I I I I I I I I
HARDING-LAWSON ASSOCIATES
lt;'l'RODUCT IQ:,
'l'nis report presents the results of our soil and geologic
hazards investigation for the planned Bishop Ranch Business
Park, Lot 1, San Ramon, Contra Costa County, California. As
shown on the Geologic Map, Plate 1, Lot 1 is situated in the
level floor of San Ramon Valley east of the I-80 freeway anc
north of Norris Canyon Road.
Two buildings about 50,000 square feet each are planned at
the locations indicated on the Site Plan, Plate 2. The build
ings will be two stories high and of steel and wood construc
tion. Maximum column loads will be on the order of 75 kips.
Other development will consist of paved access roadways and
parking, underground utilities and landscaping. 'l'he new eleva
tions will conform closely to the existing ground surface at
about 485 to 490 feet elevation.
Background
The property lies within a Special Studies Zone created by
the Alquist-Priolo Geologic Hazards Zones Act. The zone
encompasses all of San Ramon Valley and some of the adjacent
slopes. Mapping of faults in the area which serves to define
the zone included general geologic mapping, ground-water studies
and interpretation of aerial photo lineaments, all from a number
of sources. Many fault lines are only inferred and some con
siderable revision to fault locations ana the relative ase of
1
I I I I I I I I I I I I I I I I I I I
HA~OING-LAWSON ASSOCIATES
faults have resultea from subsecuent investigations. hear this
location, previously mapped faults are inferred faults in bec
rock based on a highly generalized interpretation of a northward
prolongation of the Calaveras fault through San Ramon Valley.
Up to the time of this investigation there has been no direct
evaluation of the geological conditions within the site and
there have been no direct indications of faulting within the
site. Previous investigation outside the site west of the I-80
freeway has shown the surf ace trace of the known active
Calaveras fault lies well to the west and would not logically
project into the site.
Object and Scope of Investigation
The object of our investigation was to confirm that there
are no geologically young active faults within the planned
building sites which would constitute a threat of surface
rupture within the expectable lifetime of the buildings. Also,
we have evaluated the general geology and seismicity with regard
to any other geologic hazards including earthquake shaking and
its possible secondary effects. In addition to the geologic
hazards evaluation, our scope of work included a soil investiga
tion to provide soil engineering criteria for the development.
The data obtained for this investigation were correlateci with
test data obtained for a soil investigation we perforrr.ea on the
adjacent site to the east for Beckman Instrurr.ents, Inc.
2
I I I I I I I I I I I I I I I I I I I
HA'2DING-LAWSON ASSOCIATES
In tor;Gulat1ng our scope of work we have considerec all of
tne results ot previous geologic investigation witn particular
regara to the strike and possible prolongation of any geolog
ically young faults in the area. The scope of work included
research of both published and unpublished geologic reports and
maps, interpretation of aerial photographs, and trenching. The
trenching consisted of two trenches located, as shown on Plate
2, so as to cover the two building sites with respect to the
predominant northwest direction of active faulting in the area.
The trenches were excavated continuously-with a backhoe to
depths ranging from 8 to 16 feet; they average about 12 feet.
The trenches were logged continuously by our geologist; the
results are presented on Plates 3 and 4.
Representative samples of the surface soils were obtained by
our engineer for a limited laboratory testing program. Test
results are presented later in this report. The seismicity is
indicated by Plate 5 showing major active faults and earthquakes
within the region. The general geology and seismicity are
discussed in succeeding paragraphs. Reference material and
aerial photos we utilized are listed at the end of this report.
GENERAL GEOLOGIC SETTING
The general geology in the vicinity of San Ramon Valley
surrounding the site is presented on the Geologic Map, ~late 1.
This map is a modified portion of the map by Brabb, et al.
3
I I I I I I I I I I I I I I I I I I I
HAIO'DING~lAWSON ASSOCIATES
(1971) to which has been adoeu the generalized locations of the
Calaveras and San Ramon Valley faults.
San Ramon Valley and the paralleling ranges to the east and
west all lie within the Coast Ranges Geomorphic Province. The
dominant structural and topographic trend is northwest. The
Calaveras fault, a part of the San Andreas fault system, approx
imately bounds the west side of the Valley and has haa obvious
influence on the structural development of the Valley. The San
Ramon Valley fault, which is less well defined by the work
accomplished to date, approximately bounps the east side as
indicated by the fault trace on Plate 1.
San Ramon Valley was once carved deeper by erosion and has
subsequently been filled by river and stream deposits to depths
up to several hundred feet. As shown on Plate 1, the site lies
centrally within the valley and is probably underlain by at
least 100 feet of alluvium.
Geologic formations exposed within the area of Plate 1 con
sist of Miocene and Pliocene age marine and nonmarine sedimen
tary rocks including the Briones, Cierbo and Orinda formations.
They crop out in the slopes surrounding the valley and extend
beneath the alluvium in the valley floor. The Quaternary age
alluvium consists of Pleistocene river and stream deposits and
overlying upper Pleistocene to Holocene age alluvial fan depos
its of north San Ramon Creek in the more immediate vicinity of
the site.
4
I I I I I I I I I I I I I I I I I I I
HARDING-LAWSON ASSOCIATES
SI'l'E GEOLOC>:
Previous Work
Previous work in the immediate vicinity of. the site includes
test borings, trenching ana shallow refractive seismic profiling
in the adjoining property to the north (Peter Kaldveer Associ
ates, September 197~). The trenching was conducted in an area
well to the east of the north line of Lot 1 so that it has no
direct bearing on the possibility of faulting within Lot 1. The
trench was excavated across the possible surface trace of a
fault indicated by a dotted symbol to be covered by the alluvium
and to be of pre-Quaternary age. The trench, excavated to a
depth of about 10 feet found no evidence of faulting. The seis
mic profile which extended into the area north of Lot 1 detected
no anomalous changes in velocity which might be indicative of
faulting within the alluvium. Two test borings indicate the
water table is relatively constant at about 30 feet aeep.
Previous investigation by others in the area west of I-680
has confirmed that the surface trace of the active Calaveras
fault approximately parallels I-680, thus essentially ruling out
any prolongation of that fault into the site. Northwest trend-
ing aerial photo lineaments and geophysical anomalies in an area
to the south of Lot 1 have not yet been explored by trenching.
These features could be due either to faulting within the upper
layers of the alluvium or to linear changes in the original
5
I I I I I I I I I I I I I I I I I I I
HARDING-LAWSON ASSOCIATES
sedimentation that deposited the alluvium. Our previous preli~
inary geological stuay (Haraing-Lawson Associates, 1979) which
incluaed review of trenching in an adjoining property to the
east (Burkland and Associates, November 1973) indicates that
these features are not due to faulting. Northwest prolongation
of the stronger lineaments and geophysical anomalies (Woodward-
Lundgren & Associates, October 1972) would cross I-680 at least
1000 feet south of Lot 1.
Trenching Results .
The trench logs presented on Plates 3 and 4 reveal that the
site is blanketed by dark colored, highly plastic adobe-type
clays and silts in a continuous two- to three-foot-thick surface
soil zone. These soils grade downward into generally lighter
colored clays, silts and sands with occasional gravelly lenses.
Fine-grained sandy silts to silty sands predominate although a
thick lens of coarse sand and gravel was encountered in Trench
1. Most conspicuous were continuous thin layers of light brown
colored, fine-grained sand. One or more of these layers were
found at depths ranging up to about 11 feet and represent the
most useful strata by which any offsetting structures might be
detected.
As shown by the logs, the stratification within the alluvium
to the depths explored is uninterrupted except by features which
are clearly a result of normal erosional and depositional
processes expectable within the stream deposited alluvium. A
6
I I I I I I I I I I I I I I I I I I I
HA~DING-lAWSON ASSOCIATES
thicker gravel lens exposed by Trench l is bounaea on the west
by a steeply inclined erosion surrace which represents the
bottom and bank of a channel eroded into the brown silty sand
layer. Eastwar6 the gravel interfingers and grades laterally
into finer-grained brown sandy silt.
Minor structures encountered consist of minute steeply
oriented narrow fissures within the finer grained soils. These
are believed to be shrinkage cracks formed immediately below an
exposed desiccated surface.
Laboratory tests were performed on soil samples obtained
from the central portion of Trench No. 2 and are summarized
below:
Sample
l
2
Depth (feet)
2.0
5. 0
Moisture Content
( % )
24.5
12.7
Dry Density
(pcf)
89
102
Liquid Limit
52
40
SEISMICITY
Plastic Limit
22
22
Plasticity Index
30
18
Plate 5 presents, on a regional scale, the major known
active faults within the San Francisco Bay Region and the loca-
tions of epicenters for earthquakes greater than magnitude 4
during 1934 through 1976. As shown, the site lies a short
distance east of the Calaveras fault anC within about 15 and 45
kilometers, respectively, of the Hayward and main San Andreas
7
I I I I I I I I I I I I I I I I I I I
HAs;iOING-lAWSON ASSOCIATES
faults farther to the west. As snown, there have been a number
of historical earthquakes in the range of magnitude 4 to 6
centered near the Calaveras fault. Nearly all have occurred in
the area to the south of San Jose and none within the immediate
vicinity of the site.
The more notable earthquakes in the Bay Region occurred
prior to 1934, including two major earthquakes on the Hayward
fault in 1836 and 1868, and the great earthquake of April 18,
1906 on the San Andreas fault. The star symbol on Plate 5 indi-
cates the focal center for this event al~hough it preceded
1934. Early records describe an earthquake on the Calaveras
fault in 1861. Due to lack of instrumental records and the
location remote from population centers at that time, the event
is poorly documented. However, based on reported intensities,
it has been assigned a magnitude of about 6. Surface rupture is
reported in two areas, one a short distance northwest of San
Ramon Village. The location, if correct, coincides closely with
the presently located surface trace of the Calaveras fault.
There have been no significant damaging earthquakes on the
San Ramon Valley (Pleasanton) fault during historical time. Lee
and others, 1971, suggest the possibility that a sequence of
small earthquakes which occurred near Danville in 1970 may have
been caused by movement on a possible northward continuation of
the Pleasanton fault. At that time, the Pleasanton fault had
been mapped only in the vicinity of Pleasanton in Livermore
B
I I I I I I I I I I I I I I I I I I I
HA'1DING~lAWSON ASSOCIATES
Valley; there was no mappea northwaro continuation to tne vicin
ity of the eartnGuake sequence. Present mapping oi the fault
suggests it could have been responsible for the sequence
assuming that it has an eastward dip. This is consistent with
the eastward dip generally observed in the off-site trenching.
In summary, the historical earthquake records indicate a
potential for strong earthquake shaking at the site with maximum
magnitudes in the range of 6 to possibly 7 for local events on
the Calaveras fault, about 7 on the Hayward fault, and up to
8-1/4 on the San Andreas fault. Judgin~ by the historical
record and considering the lengths of the Calaveras and the San
Ramon Valley - Pleasanton faults, it would appear that of these
two nearby faults, the Calaveras fault possesses the greater
potential.
CONCLUSIONS ;..ND RECOHMENDATIONS
Based on the results of the investigation, it is our opinion
that Lot 1 contains no geologically young active faulting.
Although faulting may occur in bedrock beneath the site and
conceivably might extend upwards into the deeper alluvium, none
occurs in the upper layers. We believe that the depths attainea
by the trenches represents a time span sufficient to preclude
persistently active Holocene age faulting. Consequently, the
probability of geologically young faulting which would present a
9
I I I I I I I I I I I I I I I I I I I
HA~OlNG·lAWSON ASSOCIATES
significant threat to the type of structures planned tnrougt,
surface rupture is sufticiently small that it can be safely
disregaraed.
The property lies within a seismically active region and
future displacements on nearby active faults can be expected to
produce at least one strong earthquake within the aeveloFment
lifetime. The maximum expectable earthquake is about magnituae
6 for the Calaveras fault and about 7 and 8, respectively for
the more distant Hayward and San Andreas faults. All could
produce strong shaking although the Calayeras probably repre
sents the greater potential for high ground accelerations.
Consequently, all buildings should be designed to resist strong
earthquake shaking.
The level site and absence of nearby large bodies of water
essentially precludes other geologic hazards, either seismically
or nonseismically related such as landsliding or flooding. Soil
liquefaction as a result of strong shaking is not known to have
occurred during historical earthquakes in San Ramon Valley
although it is conceivable that such might occur in areas of
high ground-water table underlain by sandy soils. Because the
soils are comparatively stiff or dense, are capped by relatively
impervious clayey soils and because the grouna-water table is
deep, the risk of soil liquefaction and any seismically induced
ground failure would appear to be small.
10
I I I I I I I I I I I I I I I I I I I
HAROING·LAWSON ASSOCIATES
Since the surface soils are potentially expansive (shrink
ana swell with changes in moisture content), precautions should
be taken to protect footings and slabs-on-grade from the detri-
mental effects of soil shrinking and swelling. In addition,
pavements will need to be thicker than normal to offset expan-
sive soil effects.
The upper expansive soils can be blanketed with select
* fill to support shallow building foundations and
slabs-on-grade or, alternatively, the building can be supported
on foundations that extend below the zon~ of significant
seasonal moisture change. In either case, a blanket of material
of low expansion potential (select fill) should be used beneath
interior slabs-on-grade. If supported wood floors are used,
pier and grade beam foundations would be suitable to provide
protection from the detrimental effects of the expansive soils.
Specific recommendations for site development are presented in
the following paragraphs.
Site Preparation and Grading
In areas to be graded, the upper two to three inches of soil
containing roots and organic matter should be stripped and
*select fill is material of low expansion potential conforming to the following: (1) free of organic debris; (2) free of hard rocks or lumps over six inches in maximum dimension; (3) plasticity index no greater than 15; and (4) liquid limit no greater than 40.
11
I I
HA~OING-LAWSON ASSOCIATES
stockpiled for later use as topsoil or removed from the site.
I The stripped materials should not be used in compacted fills.
I I I I I I I I I I I I I I I I
Prior to fill placement, the exposed surface should be
thoroughly moistened to close shrinkage cracks to their full
depth. This may require extended presoaking or sprinkling; it
grading is performed during or following the winter rains, pre-
soaking would not be required. The exposed surface then should
be scarified to a depth of at least six inches, moisture condi-
tioned to slightly in excess of optimum moisture content, and
* compacted to at least 90 percent relativ~ compaction. Fill
material, consisting of on-site soil or select fill, should be
placed in lifts eight inches or less in loose thickness,
moisture conditioned to slightly in excess of optimum, and
compacted to at least 90 percent relative compaction.
As outlined in the subsequent section, select fill should be
placed in building areas where interior floors are concrete
slabs-on-grade. This may require excavation of existing natural
soils to provide the required thickness.
*Relative compaction refers to the in-place dry density of soil expressed as a percentage of the maximum dry density of the same material, as determined by the ASTM Dl557-70(C) test method. Optimum moisture is the water content (percentage by weight) which corresponds to the maximum dry density.
12
I I I I I I I I I I I I I I I I I I I
HAJ:lOING-lAWSOO ASSOCIATES
Foundation Support
~orrnal wood and steel office buildings can be supported
satisfactorily on spread footings bottornea in either the stiff
natural soils or properly compacted fill. Because of the expan-
sive surface soils, a blanket of select fill should be provided
beneath interior concrete slabs-on-grade. The thickness and
extent of the select fill will depend upon the foundation
alternative chosen from the following table.
Select Material Thickness and Footing Depths
Alternative
Minimum Select Fill*
Thickness (inches)
Minimum Exterior Footing Depth**
(inches)
Minimum Interior Footing Depth**
(inches)
l 12 30 12
2 24 18 12
* Gravel or rock provided beneath slabs for a capillary moisture break is not included as part of the select fill thickness.
** Depth of footings measured from lowest adjacent grade.
The select fill blanket should extend at least five feet
beyond perimeter footings for Alternative 2. Wall and column
footings should be at least 12 and 18 inches wide, respec-
tively. Footing excavations should be cleaned of all loose soil
and be kept moist prior to placement of concrete.
13
I I I I I I I I I I I I I I I I I I I
HA~DING-LAWSON ASSOCIATES
F~otings can be ciesignea to impose dead load bearing pres
sures of 2000 psf ana total design loads of 3000 psf including
wind or seismic loads. We judge that postconstruction settle
ment of normally loaded footings, constructea as recommended,
will be less than 1/2 inch.
If structures have "conventional" wood floors with no
interior concrete slabs-on-grade, the structures can be
supported on drilled pier and grade beam foundations. We recom
mend that the piers extend below the zone of significant
seasonal moisture change and should be poured in contact with
firm natural soil or compacted fill. The piers should be a
minimum of 6 feet below pad grade. Piers drilled in groups
should be spaced no closer than 2-1/2 diameters, center to
center. The piers can be designed on the basis of an allowable
skin friction of 500 psf on the embedded area, neglecting
support in the upper two feet below final grade. End bearing of
the pier should also be neglected in design.
The grade beam between piers should be as narrow as practi
cal (about six inches wide) and poured on moist soil to minimize
uplift pressures caused by the swelling of the expansive soils.
The grade beams should be designed to resist uplift pressures of
about 1000 psf, reinforced with top and bottom steel and
anchored to the pier with reinforcing steel.
14
I I I I I I I I I I I I I I I I I I I
HAQDING-LAWSON ASSOCIATES
'l't1e equipment used to drill tne pier holes should proauce a
hole free from a surface film of weak disturbed material so that
the concrete will be in contact with undisturbed supporting
soi 1. Loose material should be removed from the bottom of the
pier hole. Soil in the pier holes and grade beam excavations
should not be allowed to dry and crack prior to pouring con
crete. Periodic sprinkling or watering may be required to keep
the soils moist.
Slab-on-Grade Floors
Interior concrete slab-on-grade floats should be underlain
by at least four inches of clean, free-draining gravel or
crushed rock to provide a capillary moisture break. Where
migration of vapor through the slab would be detrimental, a
vapor barrier should be provided.
As previously discussed, expansive soils beneath slabs may
cause heaving and cracking. The risk of damage can be reduced
by wetting the soils to a high moisture content to cause expan
sion before construction. The moisture content should be main
tained one to three percent above optimum. To help prevent
moisture change in the expansive clays, they should be blanketed
with at least 12 inches of select fill, as described previously.
For exterior decks and walks, the effects of subgrade
shrinking and swelling will be reduced by maintaining a high
moisture content. The best method of protection would be to
provide a blanket of select fill; however, the normal watering
15
I I I I I I I I I I I I I I I I I I I
HAJ<'OING·LAWSON ASSOCIATES
ot around vegetation arouna the decking may oe sutficient.
Intermittent watering is not the best method of edge protection,
but we believe that it is a practical and effective methoa ot
lessening the effects of the expansive soils as oppo9ea to the
high initial cost of providing a relatively maintenance free
section (select fill blanket}. As with all pavement construc
tion in expansive soil areas, there will be some maintenance
required especially at the edges.
In addition, exterior slabs-on-grade should be designed to
move vertically with respect to structur~s. ~eakened joints
should be provided to control cracking, and wire mesh incor
porated to help prevent separation.
Flexible Pavements
Pavement thicknesses for roadways and parking areas are
based on the quality of the final subgrade soil and the antic
ipated traffic (Traffic Index). We recommend that during con
struction, resistance value (R-value) determinations be made to
evaluate t.he soil quality at subgrade level. With estimated
traffic indexes and R-value test results, an economical pavement
thickness could be determined.
For preliminary design, considering the soil types present
at the site, we computed the following thicknesses.
16
I I I I I I I I I I I I I I I I I I I
HARDING-LAWSON ASSOCIATES
Preliminary Asphalt Pavement Design
Thickness (inches)
Material
Asphalt Surfacing
Class 2 Aggregate Base
lJriveways and Truck Traffic
2-1/2
12
Automobile Parkino
2
8
Class 2 aggregate base should have an R-value of at least 78
and conform to the requirements of Section 26, State of
California "Caltrans" Standard Specifications dated January
1978. The aggregate base should be plac~d in thin lifts in a
manner to prevent segregation, uniformly moisture conditioned,
and compacted to at least 95 percent relative compaction to
provide a smooth, nonyielding surface.
Additional Soil Engineering Services
Prior to construction, we should review the final plans and
specifications for conformance with the intent of our recom-
mendations. Substantial changes in the nature or design should
be reviewed by us and our conclusions either verified or modi-
fied, as required.
17
I I I I I I I I I I I I I I I I I I I
HAIO'OING-lAWSON ASSOCIATES
RE.FERE.NC!:.S
1. Bolt, B. A., and R. D. Miller, 1975, Catalogue of Earthquakes in Northern California and Adjoining Areas, 1 January 1910 - 31 December 1972, Seismographic Stations, University of California at Berkeley.
2. Borcherdt, R. D., 1975, Studies for Seismic Zonation of the San Francisco Bay Region, U.S. Geological Survey Professional Paper 941-A.
3. Brabb, Earl E., et al., 1971, Prelirr,inary Geologic 1'1ap of the Mount Diablo - Byron Area, Contra Costa, Alameda, and San Joaquin Counties, California, Basic Data Contribution 28, USGS and HUD.
4. Brown, R. D., Jr., and W. H. K. Lee, 1971, Active Faults and Preliminary Earthquake Epicenters, 1969 through 1970, in the Southern Part of the San Francisco Bay Region, USGS Miscellaneous Field Studies Map MF-301.
5. Burkland and Associates, November 1973, Geologic and Seismic Hazards Investigation, Winston Valley, Contra Costa County, California.
6. California Department of water Resources, 1964, Crustal Strain and Fault Movement Investigation, Bulletin 116-2.
7. California Department of Water Resources, 1966, Evaluation of Ground Water Resources, Livermore and Sunol Valleys, Bulletin 118-2, Appendix A.
8. California Department of Water Resources, August 1967, Evaluation of Ground Water Resources, South Bay, Appendix A: Geology, Bulletin 118-1.
9. California Division of Mines and Geology, 1972, Preliminary Earthquake Epicenter Map of California, 1934-1971 (June 30), Seismic Safety Information 72-3.
10. Gibson, W. M., and H. A. Wollenberg, 1968, Investigations for Ground Stability in the Vicinity of the Calaveras Fault, Livermore and Amador Valleys, Alameda County, California, Geological Society of America, Volume 79, pp. 627-638.
18
I I I I I I I I I I I I I I I I I
HA~DING·LAWSON ASSOCIATES
11. Harding-Lawson Associates, November 11, 1971, Seismic Risk Assessment, The Bishop Ranch Property, Contra Costa County, California.
12. Harding-Lawson Associates, October 22, 1973, Preliminary Soil and Geologic Investigation, Planned Danville Country Club, Danville, California.
13. Jennings, Charles W., 1~75, Fault Map of California with Location of Volcanoes, Thermal Springs and Thermal ~ells, California Division of Mines and Geology, California Data Map Series, Map No. 1.
14. Peter Kaldveer & Associates, September 1979, Fault Location Study, Proposed Commercial Development for Frank Henry Associates, San Ramon, California.
15. Lee, W. H. K.; M. S. Eaton; and E. E. Brabb, 1971, The Earthquake Sequence Near Danville, California, 1970, Bulletin of the Seismological Society of America, Vol. 61, No. 6 , pp. 1771-179 4.
16. Radbruch, D. H., 1968, New Evidence of Historic Fault Activity in Alameda, Contra Costa, and Santa Clara Counties, California, Proceedings of Conference on Geologic Problems of San Andreas Fault System.
17. Saul, Richard B., March 1967, The Calaveras Fault Zone in Contra Costa County, California, California Division of Mines and Geology, Mineral Information Service, Vol. 20, No. 3.
18. Woodward-Lundgren & Associates, October 1972, Active Fault Investigation and Preliminary Soil Investigation, Bishop Ranch, Contra Costa County, California.
19. Woodward-Lundgren & Associates, 1973, Environmental Geotechnical Input, Contra Costa County Assessment District 1973-3, San Ramon, California.
Aerial Photographs
AV-1056-02-05 to 07 AV-334-21-23 to 26 AV-353-23-32 to 39
5/24/72 7/2/59
5/23/57
19
1:12,000 1:8,500 1:12,000
I I I I I I I I I I I I I I I I I I I
Plate l
Plate 2
Plate 3
Plate 4
Plate 5
6 copies:
ECW/CBW/jd
HAQDING·LAWSON ASSOCIATES
PLAT LS
Site Location and Geologic Map
Site Plan and Trench Location
Log of 'lrench l
Log of Trench 2
Active Fault and Earthquake Epicenters
• DISTRIBUTION
Sunset Development Company 1819 Barcelona Street Livermore, California 94550
Attention: Mr. M. R. Mehran
20
1~ Cot'lloci
I _,~.o• Fault
t.vff: Modified from Brr;:ibb, etol, 1971.
IARDING. LAWSON AS£0CIATES
@ CoMulting Engineers arni Geologist1
No. 8924,004.03 Appr· Ow Date 1 / 2/SJ
' ': IS' SITE '\ .,, . .., .....
..,, . :
FQRMATIQfi sYMBO'~
Oal Unconiolidoted allu..-ium, cloy, 1itt,MJnd,orid 9rovel stre-om ledtments.
To Orinda formation, non·rnorine muds!'one, sil1sfone 1
sandstone and ~lometote.
Tc Oerbo son<!>~ forn-oton.
Tb Sriooe1 sondstor.e i:imotlon.
GEOLOGIC MAP
Bishop Ranch Business Park San Ramon,
Contra Costa County, California
PL ATE
1
REQUEST FOR CEO LUCIC llliV I LW
To: Jim Baker
of:
~ ~itial Study ~eologic Report __ Soils Report (check both if combined report)
for:
Single Site File # _1...-Minor Subdivision File # M.S. S.-V - (,i':;,
Major Subdivision File# Sub. ------located in: (District)
Date:
On: 7-1/2 Min. Quadrange -------------- Parcel No.
Hearing Date: 6- 2 } -- '6 D
Pi ease comment by: 15 1 :j i!;O (Deadline Date)
Respond to: J)/7 ;':/ (Planner's Name) ----"--'-~-------
(Phone Extension) -------
File is: Attached _,At My Desk
==-z~-6 In Main File c.abinets
Note: (Special Requests)
I
I I I • ., erences:
·-. -.
o.
. .
Cfifornia Division of 0 es & Geology, C"
5, Fault MqJ of ~
C(iforni a, ond Bolt & ""'Z-' ler, 1975, Catalogue
' . .. l
. earthquakes in Northern C ~ornia, updated in June 17, by R. Uhrhammer.
~-------~~
I o 10 20 30 40 50 Km.
0 10 20 30 40 Miles
kROING- LAWSON ASSOCIATES
@ Consulting Engineers and Geologists
8294,004.03 ~ 1/2/80 ..;b No _______ Appr· Date
EXPLAN.4TICN
SYM9CL
4 0 -4 4
4 5- 4 9 50-54 55-59
~~ oi~··'.:'J¢::'{j:~~~ .. - '
f ...
ACTIVE FAULTS 8 EARTHQUAKE
EPICENTERS, SAN FRANCISCO
BAY REGION 1934-1976
Bi shop Ranch Business Park
. - ·•.'. I • ·~ ,.
PLATE