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GEOLOGIC AND SEISMIC HAZARD INVESTIGATION

BUCHANAN OAKS OFFICE AND INDUSTRIAL PARK

Concord, California

Prepared for

DUFFEL FINANCIAL & CONSTRUCTION CO.

Concord, California

by

BURKLAND AND ASSOCIATES 333 Fairchild Drive

Mountain View, California

JUNE 1973

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and AsSOCIATES CONSULTANTS IN ENGINEERING GEOLOGY • GEOPHYSICS ENVIRONMENTAL GEOLOGY • SOIL AND ROCK MECHANICS

333 FAIRCHILD DRIVE • (P.O. BOX 820) • MOUNTAIN VIEW, CA 94040 • (415) 969-3990

File No. K3-0105-Ml 11 June 1973

Duffel Financial & Construction Co. 1882 Diamond Boulevard - Suite 450 Concord, California 94520

Attention: Mr. Marshal De Bisschop

Subject: Buchanan Oaks Office and Industrial Park Concord, Contra Costa County, California GEOLOGIC AND SEISMIC HAZARD INVESTIGATION

Gentlemen:

As authorized by Mr. De Bisschop, we have completed an investigation and evaluation of the geologic conditions at the site of the proposed Buchanan Oaks Office and Industrial Park.

As indicated in the report, the active Concord Fault was found to cross the easterly portion of the property. The presence of this fault does not, in our opinion, preclude development of the property, but it does restrict a zone along the fault from use for office and industrial structures.

The attached report presents the data gathered during the course of our investigation, the conclusions drawn from that data, and our recommendations relating to the proposed development. The investigation was performed under the direction of Mr. Murray Levish, Engineering Geologist.

• MOUNTAIN VIEW SACRAMENTO SAN DIEGO

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-File No. K3-0105-Ml 11 June 1973

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If there are any questions regarding the contents of this report, please contact the undersigned.

Very truly yours,

BURKLArfb 10:D ASSOCIATES .. ,..,. /,J

6f0cf/5/d_/ Phi:),.ip V. Burkland Certified Engineering Geologist 513

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Copies: 4 to Duffel Financial & Construction Co. l to Goetz, Hallenbeck & Goetz (Attn: Mr. Hallenbeck)

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(ii) BURKLAND- AND ASSOClATES

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File No. K3-0l05-Ml 11 June 1973

If there are any questions regarding the contents of this report, please contact the undersigned.

Very truly yours,

BURKLAND AND ASSOCIATES

Philip v. Burkland Certified Engineering Geologist 513

pp

Copies: 4 to Duffel Financial & Construction Co. 1 to Goetz, Hallenbeck & Goetz (Attn: Mr. Hallenbeck)

(ii) BURKLAND AND ASSOCIATES

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TABLE OF CONTENTS

LETTER OF TRANSMITTAL

INTRODUCTION

Purpose and Scope Methods Location and Description of Site Geologic Setting

INVESTIGATION PROCEDURES AND RESULTS

Literature and Map Review Air Photo Interpretation Geologic Reconnaissance Exploration Trenching

SEISMIC HAZARDS

Primary Effects Secondary Effects

CONCLUSIONS

RECOMMENDATIONS

LIMITATIONS

SELECTED REFERENCES

LIST OF FIGURES

Figure 1 - Site Location and Active Faults Figure 2 - Fault Location by Others Figure 3 Geologic Site Plan Figures 4, 5 and 6 - Log of Test Trenches (pocket)

(iii)

Page No.

1 1 2 2

5 7 8 8

12 13

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File No. KJ-0105-Ml 11 June 1973

INTRODUCTION

Purpose and Scope

This report presents the results of a detailed geologic

investigation at the Buchanan Oaks Office and Industrial

Park, Concord, Contra Costa County, California.

In a recent publication by the U. s. Geological Survey

(Miscellaneous Field Studies Map MF-505, Robert v. Sharp,

1973), the active Concord Fault is shown crossing the site.

The purposes of this investigation were to investigate the

possible presence of an active fault, and if found, to

evaluate its affect on the planned structures.

Methods

This investigation consisted of research and review of

relevant soils and geologic maps and reports, interpretation

of aerial photographs of the site and its environs, and

geologic mapping of exploration trenches. The investigation

of this site was done in conjunction with a similar geologic

investigation of the Cyclotron Corporation site, located at

the north end of the Industrial Park. The results of that work

are being reported separately to William F. Jones, Consulting

Engineer.

1 BURKLAND AND ASSOCIATES



Location and Description of Site

The Buchanan Oaks Office and Industrial Park consists of an

irregularly shaped triangular parcel, located beyond the

north end of the existing Stanwell Drive and Bisso Lane,

Concord, Contra Costa County, California. The Contra Costa

Flood Control Canal forms the western boundary and the Southern

Pacific Railroad right-of-way forms the easterly boundary.

The southern boundary is formed in part by the existing

Stanwell Industrial Park and in part by private undeveloped

land. The southwesterly portion of the Buchanan Oaks Park

is presently being developed, while the easterly portion is

presently vacant and undeveloped.

The undeveloped property is generally flat, covered with

grasses and weeds, and a few scattered oaks in the southeast

corner. A small pond, a water well and an abandoned farm

house area are also located in the southeastern corner of

the property. A water main crosses the property in a northerly

direction from the end of Bisso Lane.

Geologic Setting

The site is in the northern portion of the Ygnacio Valley.

The major portion of the site is underlain by Quarternary

Alluvium consisting of interbedded sands, clays, silts and




gravels in varying mixtures. Bedrock occurred at a shallow

depth in the northeastern portion of the Cyclotron site at

the north end of the Industrial Park property. This bedrock

was not geologically dated but is thought to be of Tertiary

Age consisting of siltstones, claystones and poorly cemented

sandstones. These rocks may be similar to those exposed in

the refinery property to the north.

Earlier reference maps show the Concord Fault in the area

of the subject property. It was not, however, mapped as

active by the U. S. Geologica·1 Survey on their "Active

Fault Map" of 1970 (Brown), or their "Seismicity Map" of

the Greater Bay Area, open file 1972 (Lee, et al.). The

latter map does show a grouping of small earthquake epi

centers along the trend of the Concord Fault. Figure 1

shows the site in relation to the active faults mapped by

the U. s. Geological Survey in 1970 and 1972.

As can be observed from Figure 1, other Bay Area faults which

could affect the property with respect to ground shaking from

future earthquakes include the Franklin-Calaveras Fault,

approximately 4 miles to the west; the Hayward Fault, approxi

mately 14 miles distant; and the San Andreas Fault, more than

30 miles west of the property.


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FAULTS THAT ARE HISTORICALLY ACTIVE

OR THAT SHOW EVIDENCE OF

GEOLOGICALLY YOUNG SURFACE DISPLACEMENT,

SAN FRANCISCO BAY ' A PROGRESS REPORT•

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REGION l

OCT. 1970

ROBERT D. BROWN, JR.

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INVESTIGATION PROCEDURES AND RESULTS

Literature and Map Review

The geologic literature was reviewed regarding possible faults

located in the vicinity of the site and the width of fault

rupturing during earthquakes. A compilation of previously

mapped faults in the Concord-Ygnacio Valley area is presented

on Figure 2. As can be seen from the compilation, the geo-

logic structure in the area is highly complex. Some of the

data may also be in conflict,. that is some of the fault lines

may represent the same feature, plotted at different locations

by different authors.

The significant find from the review of the recent literature

is that none of the faults in the Ygnacio Valley area was

considered active until Sharp's 1973 publication. Poland

(Master Thesis 1935) indicated that the Concord-Riggs Canyon

Fault was active.

A review of seismicity data compiled by the U. s. Geological

Survey (open file map, Lee, et al., 1972) indicates a con-

centration of microseismic activity in the area extending

northward from Mt. Diablo to Concord.



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FAULT LOCATIONS 8Y OTHERS

-TOLMAN (1931)

- POLAND (1935) 6£DL061CAL SOC of SACRAMENTO f1964)

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A list of references used in the investigation is presented

at the end of this report.

Air Photo Interpretation

Black and white and black and white infra-red stereo aerial

photographs of the site and its environs were studied to

determine any evidence for an active fault on the property.

The infra-red aerial photographs were flown on 30 April 1973,

at a scale of 1 inch to 1,000 feet. The other aerial photo

graphs are dated 1946 and 1948 at a scale of 1 inch to 1,000

feet, and 1952 at a scale of 1 inch to approximately 1,667 feet.

The traces of recently active faults can generally be recog

nized on aerial photographs by contrasts in vegetation and soil

types across the fault; and by topographic features such as

scarps, troughs, notches in hillsides, parallel ridges, off

set drainage channels, sag ponds, and closed depressions. A

study of the black and white aerial photographs did show

evidence of an active fault within the site, generally parallel

to the east property line. The data consisted of sag ponds,

drainage offsets, and a sharp tonal difference along a lineament*.

*Lineaments are defined as linear features on aerial photographs which indicate differences in vegetation, groundwater, soils, etc.




Geologic Reconnaissance

The region was examined for evidence of recent faulting

and fault creep along the suspected Concord Fault trace.

Beginning at the canal, the fault trace was seen there as

gravels in vertical contact with bedrock. In the southern

part of the property, there is a sag pond and a low, but

distinct topographic scarp. Further south, there was evidence

in the School District Corporation yard of offset fences.

Continuing south, there are many springs, offset curbs and

topographic scarps. These features along the trend of the

fault all indicate active tectonic creep.

Exploration Trenching

Five exploration trenches were excavated and examined in May

1973. Trenches No. 4 and 5 were excavated across the Cyclotron

site at the north end of the property. The locations of the

trenches are shown on Figure 3.

The trenches were excavated with a trenching machine with a

bucket width of 24 inches to depths varying up to approximately

11 feet below the ground surface. Sidewalls of the trenches

were examined and continuously logged by our geologists prior

to loosely backfilling the trenches at the end of each day.


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Geologic logs of the five trenches are presented at a.scale of

1 inch equals 5 feet on Figures 4, 5 and 6 (pocket).

As shown on the trench logs, the alluvium at the west end

of the trenches is in fault contact with weathered siltstone

and tan silty clays exposed at the .east end of the trenches.

The fault zone is characterized by a series of distinct planar

shear zones which have separated and off set materials on either

side of the shear zones. The maximum width of the fault zone

is 50 feet within the areas explored by trenching.

As indicated on Figure 3, the general trend of the fault within

the site is N30-3S°W. It appears to curve slightly to the west

between trenches 3 and 4. The fault planes vary from a steep

southwest dip at trench 2 to near-vertical at trench 3 to a

steep northeast dip at trenches 4 and 5. Relative displacement

on the fault appears to be up on the east side. Topsoil on the

east side of the fault was observed to be less than 1-1/2 feet

thick, in some locations, while on the west side it appeared to

be more than 3-1/2 feet thick. Horizontal (strike-slip) move

ment has probably occurred within the site (as evidenced by ob

served creep elsewhere on the fault), but evidence of horizontal

displacement was undetectable within the trenches. The fault

forms a groundwater barrier at this location. Free water entered




the trenches at depths varying from approximately 3 - 8 feet

on the east side of the fault. West of the fault, the trenches

were dry to their total depth of 11 feet. Boring data within

the property indicate the water table is at a depth of approxi

mately 18 - 20 feet on the west side of the fault.

Fault f~atures within the trenches were not only observed by

members of our staff, but also by representatives of the

California Division of Mines and Geology.




SEISMIC HAZARDS

The San Francisco Bay Area is considered seismically active

and contains a number of active faults (see Figure 1). A

seismic evaluation of a given site is dependent upon the

seismicity of the area, the location of the site in relation

to an active fault, the foundation or soil conditions, and

the nature of construction. Seismic hazards are subdivided

into primary and secondary effects.

Primary Effects: The primary effects are those generated by

differential movement across an active fault. Such movement

could result in ground rupture, in regional uplift, and/or

subsidence. Rupturing could be rapid as in a moderate to

large earthquake or it could be slow as~in tectonic creep.

In either case, rupturing of a fault trace could be detrimental

to any structures, including utilities which are located in

the ground rupturing zone. The width of such a rupture zone

is generally less than 60 feet. The 60-foot width is common

in areas of relatively soft and saturated alluvium. Widths

less than 60 feet, usually 20 feet or less, are common in bed

rock areas or where the groundwater table is deeper than 50

feet.


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In an attempt to determine the setback distance from the fault

at the site, we examined the fault exposures in the trenches

and the surrounding area to determine which side of the fault

was moving relative to the other. Based on the exposed geology,

it was determined that the east side was moving upward as all

the shearing was confined to the eastern block and minor shear-

ing was observed in the alluvium. The width of the alluvial

shear zone was less than 10 feet usually 2 to 3 feet. In the

eastern block, the width was 30 to 40 feet. Creep evidence

elsewhere on the fault (see Sharp, 1973) indicates right-lateral

(horizontal) movement of as much as 15 cm. since 1950. There

is evidence to suggest that the creep movements are related to

the October 1955 earthquake (magnitude 5.4) whose epicenter

is plotted very near to the trace of the Concord Fault. Sharp

suggests that rather than being continuous, the creep movement

may have either been initiated, or accelerated, by the 1955

earthquake, and that it may have terminated by the early 1960's.

This would account for the fact that the Contra Costa County

Water District reports no damage to their water main which

was constructed across the property in 1962.

Secondary Effects: Secondary effects of earthquakes are those

phenomena which result from the ground shaking. These effects

are not necessarily confined to the close proximity of an


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active fault but could be a result of an earthquake on any of

the active Bay Area faults. An evaluation of each of these

secondary effects is presented below.

Liquefaction occurs when low density, saturated, fine-grained,

granular soils are vibrated; this can be caused by shaking

which occurs during an earthquake. The saturated, fine-grained

granular soils can be temporarily turned into a heavy liquid

suspension when the relatively unstable grain to grain contact

is upset by shaking. In this "liquified" state, the soils

have little or no strength; this can result in settlement of

structures, floating of underground utilities, sand boils, etc.

Based on the results of this investigation, it is our opinion

that the potential for liquefaction is minimal at this site.

Lateral spreading generally occurs in areas of soft saturated

deep alluvium and consists of large masses of soil moving

toward open slopes. Lateral spreading may be a problem along

the banks of the Contra Costa Flood Control Canal but will

probably not affect the site itself.

The site is considered free of landslide hazards.

Lurch cracking is a type of ground rupture caused by shaking.

In general, it occurs in weak, saturated soils. There is a

possibility that minor ground lurching will occur to the east of




the fault zone. The possibility of ground lurching west of

the fault is considered minimal.

Structural damage from ground shaking is caused by the trans

mission of earthquake vibrations from the ground into the

structure. The variables which determine the extent of shaking

damage are (1) the characteristics of the foundation materials,

(2) the design of the building or structure, (3) the quality of

the materials and workmanship used during construction, (4)

the magnitude and location of the earthquake, and (5) the inten

sity and duration of the shaking.

The amplitude of ground motion is usually greater in soft

soils and loose fills than in firm soil, properly compacted

fills, or solid rock. The most destructive effects of a

shock are usually seen in areas where the ground is unstable,

and structures are poorly designed and constructed. The

vibrational characteristics of the area should be considered

by the structural engineer in the design and construction of

all improvements.




CONCLUSIONS

The following conclusions are based on our evaluation of

data obtained and studied during the investigation of the

site as described herein.

1. The active Concord Fault crosses the property within

the "zone" shown on Figure 3. The presence of the

fault does not, in our opinion, preclude the use of

the property for industrial building, but it does

place certain restrictions or limitations on its use

(see Recommendations).

2. The fault is a well-defined planar shear zone consist

ing of several shear planes within a zone 30 to 50

feet wide. The fault planes vary from steeply dipping

to the northeast, to near-vertical, to steeply southwest

dipping.

3. Field evidence indicates that the east side of the

fault has moved up relative to the west side. Vertical

movement appears to have been recent enough to offset

the topsoil horizon on either side of the fault. Creep

evidence elsewhere on the fault (see Sharp, 1973) indicates

right-lateral (horizontal) movement of as much as 15 cm.

since 1950.


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4. West of the fault zone the subsurface materials consist

of dense, relatively undisturbed alluvial soils. Ground-

water on the west side of the fault is at a depth of

approximately 20 feet. Within and east of the fault

zone, the exposed materials appear to be sheared and

locally soft. East of the fault, groundwater was found

at depths varying from 3 to 8 feet below the ground sur

face.

5. The primary seismic hazards of surface faulting and/or

tectonic creep are considered high within the fault zone.

6. Secondary seismic hazards, such as landsliding, lateral

spreading, lurch cracking and liquefaction are considered

minimal in the alluvium west of the fault. Liquefaction

may be of some minor consequence east of the fault if

saturated, low-density granular soils are encountered.

The materials observed in the trenches at this site do

not appear to be susceptible to liquefaction. Minor

lurch cracking of the ground surface for short distances

to the east of the fault may be a potential hazard because

of the shallow groundwater, the apparent structural re-

lationship of the fault blocks, and the observed shearing

in the trench excavations.




7. Ground shaking at the Buchanan Oaks site can result

from earthquakes ,generated on the Concord Fault, or

from moderate to large earthquakes on other Bay Area

faults. The response characteristics are expected to

be different on the west side of the fault from those

on the east side, primarily because of the difference

in groundwater levels. Shaking on the east side is

expected to be more intensely felt than on the west

side.

8. Peak ground accelerations on the order of 0.2g to 0.3g

should be anticipated at this site from a moderate

earthquake (magnitude 5 - 6) on the Concord Fault, a

moderate to large earthquake (magnitude 6 - 7) on the

Hayward or Calaveras Faults, or a large earthquake

(magnitude 7 - 8+) on the San Andreas Fault.




RECOMMENDATIONS

1. Because of the high hazard from future fault rupture

or tectonic creep, it is recommended that office or

industrial buildings not be constructed within the

fault zone shown on Figure 3.

2. Since future rupturing may not necessarily be confined

to the zone of previous movement, and since some margin

of safety seems reasonable in the circumstances, it is

recommended that permanent structures be set back some

distance from either side of· the· identified fault zone ..

Our evaluation of the exposed materials and our review

of the literature regarding ground rupturing, leads to

the conclusion that 25 feet is a reasonable distance

for setback from the west side of the fault zone. A

greater distance is recommended, however, for building

setback on the east side. It is our opinion that 60

feet is a more appropriate distance from the east side

because of the potential for lurch cracking and secondary

shearing within the eastern block. A setback of less than

60 feet may be used east of the fault, but it should only

be done with the understanding that there is added risk.




The recommended setback distances at this site are

25 and 60 feet from the west and east sides of the

fault zone, respectively. If a lesser distance is

chosen for the east side, it should never be less than

25 feet, however.

3. The fault zone and the area within the setback lines

may be used for facilities related to industrial use

such as roadways, parking areas, spur tracks, or open

space. It should be anticipated that any such facilities

placed in the setback zone, and particularly within the

fault zone, will be subject to maintenance or repair in

the event of creep movements or sudden ground ruptures

along the fault.

4. It is recommended that major utility lines avoid crossing

the fault if possible. Where they must cross the fault,

consideration should be given to providing flexible

connections, and/or emergency shut-off valves.

5. The trench locations and fault zone have only been

approximately located in the field. For specific planning

of building layouts, etc., it is recommended they be lo

cated by survey methods. The backfill in the exploratory


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6.

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trenches should be recompacted since it was only

loosely dumped in the trenches after examination.

The locations and conditions of the backfilled

trenches should be considered in the design and con

struction of any foundations or related improvements

in the areas of the trenches.

Specific soil and foundation investigations are

recommended for each of the proposed building sites . once the building types and locations are chosen.

Construction and grading east of the fault may be

adversely affected by the shallow groundwater con

ditions. A qualified soil engineer should be

consulted if any development is planned in these

areas.




LIMITATIONS

This investigation has been based upon surface reconnaissance,

studies of aerial photographs, review of geologic literature,

and inspection of trench excavations. No inference should be

drawn from the language of the report that the scope of the

investigation was any wider. It must be understood that

although the observed and reported conditions are considered

to be representative, local variations and geologic conditions

may exist for which this firm cannot assume responsibility.

This report was prepared upon your request for our services,

and in accordance with accepted standards of professional

practice. No warranty as to the contents of the report is

intended, and none shall be inferred from the statements or

opinions expressed. This report completes our contract re

quirements.




SELECTED REFERENCES

1. Brabb, Earl E., Sonneman, H.S. and Switzer, John R., Jr., 1971, Preliminary Geologic Map of the Mt. Diablo-Byron Area: Contra Costa, Alameda, and San Joaquin Counties, California, U. s. Geological Survey Open File Map.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Brown, R. D., 1970, Faults That Are Historically Active or That Show Evidence of Geologically Young Surface Displacement, U. S. Geological Survey Open File Map.

California Department Water Resources, 1931, Economic Aspects of a Salt Water Barrier Below Confluences of Sacramento and San Joaquin, California Department Water Resources Bulletin No. 28, pp. 450.

California Division of Mines and Geology Bulletin 181, 1962.

Davis, F. F. and Goldman, H. B., 1958, Geologic Map of Contra Costa County, California Journal of Mines and Geology, Vol. 54, No. 4, Plate 5.

Geological Society of Sacramento, 1964, Annual Field Trip to the Mt. Diablo Area.

Gribaldo, Jones and Associates, 1972, Soil Investigation for The Cyclotron Corporation office/plant building, Contra Costa County, California.

Ham, C. K., 1952, Geology of Las Trampas Ridge, Berkeley Hills, California, California Division of Mines and Geology, Special Report 22.

Jennings, C. W., Burnett J. L. 1961, Geologic Map of California, San Francisco Sheet, published by the California Division of Mines and Geology.

Lawson, A. C., 1913, Areal Geology of the Concord, California Quad: San Francisco Folio, Geologic Atlas of the United States, u. s. Geological Survey.


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11. Lee, W. H.K., et al., 1972, Seismicity Map of the Greater San Francisco Bay Area, California 1969-1972, U. s. Geological Survey, Open File Reports.

12. Poland, 1935, Unpublished Master Thesis, Stanford University.

13. Rogers, Thomas, H., 1966, Geologic Map of California, San Jose Sheet, published by the California Division of Mines and Geology.

14. Saul, Richard, 1973, Geology of the Southwest Corner of the Walnut Creek Quadrangle: Unpublished Map.

15. Sharp, Robert V., 1973, Map Showing Recent Tectonic Movement on the Concord Fault, Contra Costa and Solano Counties, California, Miscellaneous Field Studies Map MP 505, Basic Data Contribution 55.

16. Wallace, R. E., 1968, Earthquake of August 14, 1966, Varto Area Eastern Turkey, Bull, Seis. Soc. of Amer., Vol. 58, No. 1, pp 1-47.


OVERSIZED -DOCUMENT HAS

BEEN PULLED AND SCANNED WITH THE MAP

FILE.

6f0cf/5/d - gmw.conservation.ca.gov€¦ · 11.06.1973 · i l ji • i -· j - _j 1 j' i j ]...

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