Purcell. Rhoades & Associates

1094 Stewart Drive Sunnyvale, CA 94086 (408) 733-4373

Please Reply To This Office [_I

Ms. Joetta Douglas 31694 Chicoine Hayward, California

Consultants in the Applied Earth Sciences

1335 Treat Boulevard Walnut Creek, CA 94596

(415) 935-9490

D Please Reply to This Office

November 28, 1979 Project No. 2491-S

Subject: Geologic Reconnaissance, 4200 and 4202 Rettig Avenue, Oakland, California

Reference: Soil Report by Purcell, Rhoades & Associates, dated August 23, 1979

Dear Ms. Douglas:

At your request and in response to the comments of Mr. Harold Goldman,

consulting review geologist for the City of Oakland, we are expanding our

geologic findings as related to the subject property.

SCOPE

The scope of the present work included review of relevant geologic litera-

ture, a detailed reconnaissance of the site and nearby areas, analysis of

aerial photos' and preparation of this report.

Bruce G. Purcell, C.E.G. Daniel J_ Rhoades, P.E. Wayne Pandorf, P.E.

Bill McMorrow, P _ E_

Peter E. Monk, P.E.

November 28, 1979 Project No. 2491 ~s Page 2

SITE LOCATION AND DESCRIPTION

The project site is located near the intersection of Jordan Road and Rettig

Avenue on the south side of Rettig AV"cnue in Oakland, California. The

site is bounded by priV"atc property on all sides except along Rettig AV"enue

as shown on Figures land 2. The site is irregular rectangular shaped and

covers an area of approximately • 5 acres. The site slopes to the northwest

at approximately 1:1 horizontal to V"ertical, Site relief exceeds 100 feet and

ranges from 300 feet elevation aboV"e sea level in the western portion to

over 400 feet near the southeastern boundary. The site is covered by grasses

and scattered trees.

As of the date of this publication, the planned development will consist of

2 units of single family dwellings. The units are to be typical two or three

story wood frame with related paved parking and access driV"eways, and

necessary utilities,

GENERAL GEOLOGY

The site is located in the Lower Berkeley Hills in the Western Coast Ranges

of California. These hills, like most of Northern California, exhibit a

prominent northwest structural trend, The major lithologic units in the

vicinity include serpentine and other rock types assigned to the Franciscan

Purcell, Rhoades&: Associates

November 28, 1979 Project No .. 2491-S Page 3

Formation of Late Mesozoic Age, the Leona Rhyolite of Pliocene Age, and

Quaternary alluvium. Sedimentary rocks of the Knoxville and Joaquin Miller

Formations, of Jurassic and Cretatious Age occur in the upper Berkeley

Hills, east of the site.

The Berkeley Hills have been highly folded and faulted. The active Hayward

fault is mapped at the base of the hills, extending between San Jose and San

Pablo Bay.

Major study of the Hayward fault has been conducted by Case (1963) and

Radbruch (1967 and 1969). A section of Radbruch's map of 1969 is included

as Figure 2. More detailed work in the vicinity of the site by Hallenbeck-

McKay and Associates (1978), Engeo, Inc. (l 971) and Kaldveer and Associates

(1979) tend to support Radbruch's mapping.

The Hayward fault is a complex, anastarnosed shear zone. In the vicinity

of the site it is mapped as 3 traces: the central, most active trace is located

approximately 600 feet east of the subject site; the western, least active trace

is located approximately l 000 feet west of the subject site; and the eastern

trace, considered moderately active is approximately 1500 feet east of the

site (see Figure 3).

A .definite air-photo lineation is visible along Jordan Avenue, east of the site •.

Purcell, Rhoades & Associates

November 28, 1979 Project No, 2491-S Page 4

This coincides with the central trace location as previously mapped, No

evidence of photo-lineations was discovered at the site itself •

•

The site is underlain by the Leona Rhyolite of Pliocene Age, This unit is

complex and heterogenous, containing hard and soft "'ones of rhyolite, as

well as xenolith$ of Franciscan material. The Leona Rhyolite is presumably

underlain by the Franciscan Formation. This contact is known to be locally

sheared (Kaldveer, 1979), The contact is at unknown depth. at the site, how-

ever rhyolite is exposed in the creekbed, as much as 50 feet below the subject

site.

The site is a steep slope, in excess of 2:1 vertical to horbontal (see Figure

4). No in-place exposures of bedrock exist on the site, although angular

cobbles of hard rhyolite are scattered on the ground surface.

The boring logs show that the soil horizon is deep and that the subsurface

materials are consistent across the site. The less weathered bedrock

material was found at depths of 4 and 8 feet, Of course, soil depth can be

quite variable on such steep slopes. Our site reconnaissance revealed no

visual evidence of fault offset on the site, on Rettig Road, or in the creekbed,

The steep slopes and deep weathering horizons make trenching and geophysical

exploration difficult and of limited value, The generally steep slopes on the

site show no evidence of instability. No obvious stress due to soil instability

Purcell, Rhoades & Associates

November 28, 1979 Project No. 2491-S Page 5

is apparent in the exterior walls or improvements of the hon1e s to either side

of the subject property. However, without proper surface drainage, surface

erosion and subsequent slumping could occur.

Due to the proximity of a major active fault trace, very high ground shaking

could be experienced at the site in the event of an earthquake. Peak accelera-

tions of oSO g or higher may occur in a large quake centered on the Hayward

fault {Greensfelder, 1974). Therefore, we recommend that the structures

be designed to resist sustained ground accelerations of at least .25 g,

In summary, the Hayward fault is located near the subject site, but no evi-

dence exists of subsidiary fault traces through the site itself. It therefore is

our opinion that the site may be developed provided that the development is

con~istcnt with accepted engineering practice,

If you have any quodi.ons, please call our office,

Pcspcctfully,

PUHCEJ ,J,, RHOAIJES & ASSOClATF:s

~~~~~i{~G ~~f;,~f~~~o~~

Prir1cipal

Geologist

cp

Purcell, Rhoades & Associates

REFERENCES

November 28, 1979 .Project No, 2491-S Page 6

Contra Costa County, Seismic Safety Element Technical Background Report, 1975,

Contra Costa County, 1976, Preliminary Geologic Map of Contra Costa County, Unpublished Map at 1:62, 500 Scale Available from Contra Costa County Public Works Department,

Engeo, Inc., 1977, Geologic Investigation of Excess Land Along 35th Avenue and Redwood Road, City of Oakland.

Greensfelder, R. W,, 1974, MlOximum Credible Rock Acceleration from Earthquakes in California, CDMG Map Sheet 23.

Hallenbeck, McKay and Associates, 1978, Geotechnical Investigation, College of the Holy Names Property, Monterey Boulevard, Oakland, CA.

Housner, G, W,, 1965, Intensity of Earthquake Ground Shaking near the Causative Fault: World Conference of Earthquake Engineering, 3rd, Wellington, New Zealand, Proc. VI, p. III-94-III-109.

Kaldveer, Peter, and Associates, 1979, Geotechnical Investigation, 35th Avenue Slides, Oakland, California.

Ploessel, M. R, and Slosson, J, E., September, 1974, Repeatable High Ground Acceleration from Earthquakes - Important Design Criteria, California Geology, pp. 195-199.

Radbruch, D, H., 1969, Areal and Engineering Geology of the Oakland East Quadrangle, CA. U .S.G.S Map GQ-769.

Radbruch, D. H., 1967, Approximate Location· of Fault Traces and Historic Surface Ruptures within the Hayward Fault Zone, between .San Pablo and Warm Springs, U.S.G,S. Misc, Geologic Investigations, Map I-522,

Schnabel, P, .B. and Seed, H, B., 1973, Accelerations in Rock for Earth­quakes in the Western United St.ates, Bulletin of the Seismological Society of America, Vol, 63, No. 2, pp. 501-516, ·

Purcell, Rhoades & Associates

N Figure

1

DAT£

PURCELL, RHOADES • ASSOCIATES Foundaticln Enstnnrblc • SGU ~ltnewlq • ... ...,

Site Location Map

11 /28/79 DllAWN •v MC

w.o. 2491-S

N

Figure

z

DATI: 11/28/79

PURCELi. RHOADES & ASSOCIATES Foundation En1inNriR1 • Soil Enain•ltrln* • GHIOD'

Geologic Map of Vicinity

(from Radbruch, 1969)

DRAWNBY MC CHl!CKl!D DY WP

9CALI< 1:24,000 w.o.

2491-S

....

·" . '

~' •• •

Map Source: City of Oakland

N

\\\\ \ \ Eastern

1, \ \. trace \

' '

PURCELL, RHOADES & ASSOCIATES

Figure

3

faund.atlan 1£nctn1:u1rln1 • Sall En,Jln11•riill • 8tolOIJ

DATE 11/28/79

'"°"LI< l" " 400 I

Vicinity Map, Showing three traces of the Hayward Fault

DRAWN BY MC

CH !CKl!D llY WP

w.o. 2491-S

- 310

\ PARCEL A

---

/ ,.,,----- Exi sting l'.'.:a.

small driveway.:/,. /

~-~ -~--- ··-

360

Rettig Avenue

/

PARCEL B

f'igure

4

DATE 11/28/79

sc~u . 1"=16'

Boring locations from previous soil report

PURCELL, RHOAD ES & ASSOC: IATES f"oundttiaa .Erq:;n1Nfn& • Soil Enlin•rins • -Qulo.u

Site Plan

(To po graph y a ppr oxima te) DRAWN BY CHECKED .11Y

MC WP w.o.

2491-S

-> > " < " ..

" 7 " , " ->

" ~ " f' ft. L "'"

> At:,<

Th"' locations and limitations of the geologic features shown on this map are accurate representations of said features as they exist on the ground, were placed on this map by me or under my supervision, and are accurate to the best of my knowledge

~.~~&At PURCELi., RHOAOES & ASSOCIATES

Figure

5 Geologic Map of Site Area

DA.TIC DRAWN ISY

N 12/11/79 MC GCALI! 1" " 400 1 w.o. 2491-S

D Qac Alluvium and Colluviu1n - Quaternary

0 Qsl San Antonio ·.F"orir1ation - Qll<itern~i~y

Q Ti Leona Rhyolite - Pliocene

film Kjfs FranciHcan So.nd stone and Shale

II Sp . Frar1ciscan Se rpcntine

-- Lithologic Contact, location certain

,,..,,-- --- - Lithologic Contact, location approximate

FAUL.lf ZONE SYMBOLS

-:::11 .. SP:OClt.L STUDIES ZOl~E BOUNOP.Y

- SUSPECTED FAULT TR.c.CE, STATE

--<>--- !iO' SETBACK, SUSPECTED TRACE

Note: Geology taken from Radbruch, 1969, and Site Geologic Reconnaissance

Figure

5B

D•CTEl 2/11 /79

GCA.l..E NI A

PURCELL, RHOADES & ASSOCIATES Foundst:Ian Ensineerlnt • SOil £n1ln11rln1 • a11101ou

Legend for Geologic :Map

cRAWNllY MC lc~-D~

w.c. 2491-S

A

Ti

Ti

Figure

6

SCAL!: l "=400 1

Haywad F'ault Zone main trace.-

PURCELL, RHOADES & ASSOCIATES Found•tlon rnstn11•rlnt: • son Enrlnnrinf • llil.eotoo

Cross Sections A-A' and B-B'

Dh.AWHB"'t' CH~CKEOBY

MC w.o. 2491-S

PURCELL, RHOADES & ASSOCIATES

Figure _ . SolJ Engi,,,..,.ing • Geology f!oundl!ltioti Engint1Ctn.. •

1009 STEWART, SUNNYVALE, CA • 1408! .733-073

7 · t' of Area Aerial Photo Interpreta ton . Near Site: Hayward Fault

DATE l 2/11I79 DRAWNBY MC

SCALE l "=2000' w.o. 2491-S