STATE OF CAtlfORNIA · THE RESOURCES AGfNCY

DEPAR1MCNT OF CQN~fJ!l/ATION

DIVISION OF MINES AND GEOLOGY SAN FRANCISCO DISTRICT OFFICE rERRY BUILDING

SAN FRANCISCO, CA 94111

(Phone 415-557-0633)

December 4, 1979

Lyle D. Johnson City of Millbrae 621 Magnolia Avenue Millbrae, CA 94030

Dear Mr. Johnson:

EDMUND G. BROWN JR. C:c: . .-ic-~or

We are placing on open file the following report, reviewed and approved by the City of Milibrae in compliance with the Alquist-Priolo Special Studies Zones Act:

Foundation soils investigation and geologic reconnaissance at Parcel 9B, Millbrae Highlands 6A, Millbrae, CA; by Geo-Ekta Labs and Perry Wood; Sept. 25, 1979.

Sincerely yours,

EARL W. HART Office of the State Geologist CEG 935

EWH/fn 1

cc: A-P file/

November 27, 1979

STATTI OF CALIFORNIA Division of Mines and Geology Ferry Buil<ling San Francisco, CA 94100

Subject: Geotechnical Report Millbrae Highlands 6A, Parcel 9B 10 Til Boni to Way

Dear Sir/Madam:

Attache<l, in accor<lance with State law requirements, is a copy of the geologic report on the subject residential property.

Don't hesitate to contact me should any questions arise on this subject.

r.5,

le D. Johnson Direct r of Public Works/City Engineer

swb Attachment

cc: Buil<ling Official Planning Department

621 Magnolia Avenue, Millbrae, California 94030 (415) 692-3500

~' ··• .• T William F. Jones, Inc.• Consulting Engineers Soil, Foundation and Geological Engineering 865 Woodside Way, San Mateo. California 94401 (415) 347-3826

File: 178139.8

9 November, 1979

Geo-Ekta I,aboratories

Goss and Associates, Inc.

38750 Paseo Padre Parkway

Fremong, CA 94536

H.F.C,'ElVEO

c i Y Of ~.,.: ·3FAE. C:-\. l ~I \ c.~ ~-·· '·

Attention: Dale E. Goss, P.E.

Subject: Foundation Soils Investigation

and Geologic Reconnaissance

Parcel 9B, Millbrae Highlands 6A

10 El Bonito ,way

Millbrae, California

GEOTECHNICAL REVIEW

Dear Mr. Goss:

William F. Jones, P.E. Jongsol Kim. Ph.D., P.E. C. P. Zones. R.G.

Ne have completed review of the combined subject reports in our ca-.·------

pacity as geotechnical consultants for the City of Millbrae. We are

recommending that the City Engineer accept the reports with the under­

standing that the consulting geologist's concern about the future

stability of the steep slope along J\ura Vista will be translated into

mitigating measures. One of those measures should be the provision

of adequate means for subsurface drainage. Although relatively little

shallow water was encountered during test drilling, the luxuriant

growth of pampas grass, bamboo, and other hydrophilic plants along

Aura Vista suggests that near surf ace ground water is at least locally

abundant.

Pile: 178139.8

9 November, 1979

Jf you have any questions or comments, please feel free to call or

write us.

Very truly yours,

WILLTl\M F, JONES, INC.

C.P. Zones

Principal Geologist

RG No.2928

cc: 3 to Geo-Ekta Laboratories

1 to Lyle Johnson, P.E., City of Millbrae

1 to Mr. & Mrs. Ragni

- 2 -

·:'·

' '

/~ '·· I

\....

(,

Goss & Associates,' J~c.

r ~.

,\''

GEO·EKTA LABORATORIES SOIL MECHANICS

.~ 2478 E. Fonder Ave .. Unit H Fullerton, C.llf. 92631 (714) 870-9800

387so Paseo Padre "i>arl<way Fremont, Calif. 9453r,

(415) 793-046.0

·-

F'~c'id,_•\I I UN c;JlL::; lJ·;y;.,3'.l'~l;A':'ION

MD Gf:O.l /lG LC FEC0:'NA:SSMiCE

AT

Par·cel 9D i·'.lill'r_irac }·l'.i.f)1larlds C1~

fvii1.i -~)l"·ue, Califor~:~u )L~G)O

i'<i\ ... ~'.\J) I··~~\:~;. ~,_L_'.~.:<I

i:_;· r::1 Jc,:·~_i.ta \<.:=.:,-?·2 .L 'l. t) 1 ·; •. c' , Ca .. L ·i f c r~:~ a ·.~-~c, ~\.

:: .. Ji 7f3 F:nt:Jt l•1ender Avcrr..Jc ;:\1Jlerton, CaJ ifo:rr:: a. ~-~26:.J·i

11_1,_g·1u-9f3co

~:;8750 :-Paoeo Pnd.re PLr}:y.J,\·y C~9 i~'rcmor~t, Cu.J i:f'-:ir·rlia '.·.:i4536

415-"(9:c;.-cl;64

LOUIS ATTILIO ARN Civil Enginl."!er &. Sui-~- ·

I Lcr Ci·uz Ave. Millbra~, Cn!if r .. J,~OY

tr1 3.ssocJaticr1 \-7~ ti'1

11!;, PlliiEY F:. HOOD f'.ne;:i.:r~eering Gc~o·.: ogist

1021. f)aJ.c Ave:r1ue Vi( ~ .... u1tai~·1 "':/i0w, Cal..ifcrnia 91tol1u

(!n~, )-968-2510

/- I 0 d- D"tc: Septcm\Jc' :-''_:), 1979 :> y'-1 11~ Job Number: F·G-L'(6l'1-79

i-'l"A-

.Sr.ooe ~

C~O-};{\TJ.1A T .aboro.~or:i.efl

'"i~;b =··.~u.::n1)er: FG~8}l'.::j-·.19

&...:.d Geologic f{eccm:ai:::.:3f~·1ce at the site of tt"-.l.~ p:ropO::icd constriJ.ct:i.cn

-\,:,o be located at Po.r·i.:(.·1 \)R, /,~illLr·uc liiglllt~:~do 6.A, ~,tillt~~ae, Cal:~!.'n"!'.11ia.

J::1ve:::rt:Lg<"it'.i,on wu.u u1..:. L~H..lrizcd to dctc1,ruiri.c the c..::dsti~1g :.:Joi.1 cur1di liur~[.;

at -:J1e site a:ad to fJJ:'<.~,-.. r: .. 2 (:;~·~a ;i11d :=;pi:~c:if:i.c- r·~:c..:ci::i:r:·:(;ndatio~1s r~.l.ative

to the fou.ndu. L~i nn dc.··:.~:Ll::n ..:.~or tl1e propc··~.:cci st:r"'J.ct·::.:re.

~:.i~o'...lld J'irta.l der,isr.. lcaci.s ·va"!""f sigl1ificantl::,~ .t.'rcr-. ~bo~c rnc:ntior1ed above,

"~j.s o:!'fj ce 1..:hc'"\.lld be r .. c~:i.1.~icd.

Si tc Ccir1di ti on

'2.1-_e s·:.te Of i_.J1e IYJ"'C,l.JO~.>Cd ~.:.~;u:;t.~-rJ.ctiOll i.::::· ter:raced \Yitl1 ;.l. fai:rly u:t.:.arp

relief. lt :i.f.·> 1·iormUed (.;:-1 the E.~outll by A-,.i..ra Vista, \<.'f-.1.creas; tl1e otht.:r

tJ1rc~e (3) con·LigucnJ.s pr:.::pe.rt:i.es l1aT.re 11ouses. ..._

·l'.rit.I·: refeJ·ence 'Lo ·:J18 ~;:..te ir1vcstj r.;ated, the ;:u1"'Lt. i~.; i:1igher, ti-~~= i:\_;u.tt.

is lci,.1cr, ·wb.ile; tL.e Lt:::: l n.~:; well UD tJie \i;\~u'L 1-1.:..ve 3..i..rrilH:::' co~: tee..~·:.~ ;";.~=:. -t;·!e

ut:.Li~'jc~:<.!·~ lll'(Jpcrty.

-1-

.Si.te Cor1ditivr1 (cont'd)

'It.c ~ot tilopt:f; dO'itm towardt> tJ\c Soutl-1.

CT£O-.GRl1.1\ La bora torie s Job N\:-11ber: F'C~fl76N-79

Tcrrur.:.{~d ~1alls will he rcrnoved, b1..lt tt·loSe 'i'lu.llc u.ocd alo!"lg Aura

Vista will r0n1ain for· landccnpi....1g :pu .. Iyouct1.

Ji,_ lig}1t g:r·ov..'t!l. of grauf.> ur1d weed~_; .Corm$ tl1e g.r·oL.lJ1d cc,,rcl' u.lorig ·wi.. t}-1

so1ne twerity ( 20) trees i:n tlrr·ee ()) rO'.JS ~ pl~mtec. beth:een tl1e retajJ1.i.·ne

walls.

Exr) 1.(:.r·n. t::: on

1"JH.:; ~;uL::~t:·r·i.'~1cf~ wa:3 e.:-:fllOJ't~cl. by dr·.: lli..ng five (:.;.), six (6) inch cl:i.i3Jnete1·

borings to depths oi' fifteen (1~.:,~ 'L~J thirty (JO) fee:. ~;e~.ow th.o ex.istir11;

r-;rou.rid Gt.:..1 1facc. '.l.1f1c borir.Lr~s h'e1·0 pillced in stratee:::ic le.cations v.·here

A:~ l or th~: t.n.-:;·':l..nEs l.>it·~r'e lcEgi:..~d ·'.··,y ·:~""V.I' ~·i1.~ld cr1gir:eer·;1;.~(: 1 i:l0 ...:...:cc.n.rrLciarL

ar1d botl1 l:.ndit3t'-..: .... rbcd <:.~rid d.:i..sttll'~·cJ ~.::.;-;·.pl<;.<:.; of tl1c 0uil..:.: ::::r:..co1...~.:ntere(l

were obtai.:ned for labnl"'<i.tcr"J tt::0t.: r ... g [l...l:1d i .. nE:r.)cn"'Lion .• ~r:;s cf ~lie

i.ti l1oco1~d~: ... Y~ce w~:.t:r..1. -\.LP. \1:-:if ..i..t~J '.\.:·il Cl.a:~t:;j_f:i.cu.tion D)-:=-:c:ri ::icccI·illcd or.l.

~ill att:..Lchetl Plato. 1.l'l1:Lc; P.".lalt: aJ:.;o .::.,;b:J-.,1.'3 tl10 tYJJ(~ of sll.!:Lplcr u~:..;cd ir~

cbtccininc undisturbed ca'TipleR.

-2-

CPO-PK'~A laborato2'ies

Job N"l,;.n1bcr = Ji'C-f37C;-J~ 79

·1;tE·: field rrioi~;tu.rc :_~or.ti:-.:lrL a11d dJ" .... .f de11s:.:ties (;,f the soils encow1te:red

1.·:e:ce cieter11:iried l->y pc:;."'fo1rr1ir .. g tests or1 tL.e li .. nc.l..iLJturbed s:--ur.1Jles. ..1t1e

rc~3ultt..> of th.~~_;e t.(:;-_;-l.3 1~.:.··e flhOv.'n nr1 tb.e I.cc;s er f.orings, Plates irl~ 1 '

t!~r·oup-)1 "F". Deru.;i.ty and field :noiutv..::-·e i..;:,:fc..;:r-:-n.::i..tion :i.s ll.se.t'ul as

i.Jl.dicn'Lor-8 or 'L11c natur·e a:nd qi..1tiltty of ~,l~e !:::.rterial.

:'.Ji::r.~cct sl"1ear te3ts were pc:cfo1"'rr1od on ~;cJ.ec.-tcd; lmdisturbcd Gamples

o~ tlH;. ::;o:i.ls :i..:n ord1::r· ~r:; detcrrn:Lrie tl1e strc.:-1gt!i:::: &r.cd supporti11g

ea1x.;.citiot; o:f tJ1e soil~;. 1rh(-: rne t:ftod oi' llcrfc2-:::ii.r~g these tf:sts is tc

.sa-'.::;uratc the s3lnple, to ext.rude tl1e oe.!:iplc i~-~tc the test appara tJ.s,

to i'i.!:Jply th(~ norrn.a,L 1o;~ci, o...r1d Lo tl1c.:n uJ.1.cw f'...;,!~~·:.i.cicnt ti1nc to el1ip~_;(·::

~:- ... ":J~clJtcd 'Lo n str11iI.:~co:1t:rollcd ~_;ingi.~ p)~:.~--e ~-'~~car tefJt. 'I1l1c r:-1et.bcd

.:~" arJp..'..yinr; tl·113 no:rrr.al a:-~d shec·Lrinc .Load :::_3 _:_~ . .::h as ""i:o allow t~1e sa..mple

:!.:··>:::·ozi:nutcly (),()~, ir\::;1~cJ ;)er :-:tlnu~.:c.

sa:nplcu h'CI'C also tc~"".:.cd at inc::--eascd !'J.o:r:~~::.. pr·essui~es in order to

C.etcrmine t..1--ie ir:.crea:::e ~:..::·i .'.:;Lear t.>"..:.renctL.s asso2:'...a-::.ed witI'.. i.r:c:reased

ir~terg·rurnilar JlJ'c.:~.:~_n.rr·t'.:a 71:-ic te~t I'csult~ ti.:--f: plotted grap}iicall:_.,,- on

1-12-ates "G11 and 11 11 1'. Tt".l.e rt:s·c..lt.i:nt': ·values 3.l'(: .[i.~ follows:

Soil Tyne

Clri.:,rcy fJandy si 1 t

~1:i..l ty Ba:n.d

AJigle nf In.tc~;r:71al

f•'r:i£~i nn (Dep;t·eee)

;:io J. ~U 2·

)Ii

-3-

Col1coior1 (p.oo.f.)

170

l,aborator:r 're~1ti.r1g (c::int 1d)

GEO-EKTA lx:tborti.torics

Job Nur:cbcr: PG-87CN-79

Porous stones ·placed d.t tJ:i.e tcp ar~d bet tom of ea.c.h &pecir:Jcn perrr:i t

.:'rE.1 8 flow or watc1· ir1to 01~ f1·~c,:::n ~l"lf t:;peei.rr1cn du.ri.ng the tet:t.

Su.cccssive J.nrid ir:crcrricrrts h·ere .fiI)PlieU to the top of the spcci.me:r,1.

ar1ci µrc1grcssivt~ ttlJ.Ci. J'inal ucttJ_e:nent3 u11dt~1· cu.ch i;~i:.;rc1":'lcnt ·.-:(:re

reco:r·(led to c~n. nccurac;v o:l' ().,(JliOl incl1~ 1.i'he .fi:n.til [H}.ivtlcrnen.ts ::=·;o

obtair1cd are plcJtted to detc·2.v...ci..r.."J curves sl1owr1 on. Pla~es "1 11 u:nd 11 .J 11•

ConcJ1.;.2ion3 ru1d 'R(·:corrrn(~ndcttio!-1S ~ -~)o:i l Cor:di tion --·· .. -·-

rl1he 011 s :i.'L(.~ ~.>oils a::ce con1pc;t;t"~d of clayey 3il ts 7 s :i.l ty $aLdll, st.1 ty

clayD a...1d sa~1d~r c.l.~!.y~.::. ::Lt e:C-:,E~·:d.3 "".:o the i:lei:-rth oi' -:he bc1~tri[, tl"1irty

( -,.·\ (' . _J,.1 1 . ee·\,,"

'J'he load bi:.::arin.g ~~;oils po:_;~_;c:J:J !:.ci.i.erate strenc.---:ti··. c~:.~~..-·~-:.ctf~,::·istics.

A water- to.blc wau noted :.in bor;.r:e; '.'ivo (5) at ;1 dept.Jo of t,hi:r-ty (3C:)

feet. I~~ tlo.:.·'inp; tli'O (?), wEl.ter i~-::rr.lsior:. wa.s apparc·nt at a depth 01·

t.l1irtee!! (1_5) feet. lll".Li$ f;E:er:10 to ~Je perched Wi~ter·.

Des:~

'.!'he .foundation of Uw proposed sti'llc-;:ure may ~ C.csigr_ed by usir:g

oon·tir:i.'i.l.ou.s footir.!.gs tJ_ed 'l.ogcthGr i~ a waffle J)a°ttcrtl r .. :-.:.d suppo:-rted

by pier's. (r(:ur·cd-in~-place Cl;·i.st:or1.:;)"'

App:rox:ir::ate p~_er defJth :i:3 c~:l:.·ectec~ to be f'J.f"tec11 (15) to ~'enty (~\I) ,,_, ... ,...,_ ····~ .......... " , ... ~ ....... , .. - .. -.. , --~, .. -.. ····--·"'"""···--·-·---· ..

"!.'r~et. T!1e di.ctr::J.ete:r o.!.' ·~·he pier 1':~:.11 de.rJend. on tt1e fuw:c.ation load~;,

_I+-

Det;~pi (con~ 1 fil

G.t:O-E:rr.A lfi:)c!ratories

Jo ti Number: FG-876N-79

b'J.~ a rr1i::1~.rnm.n of i'o\.rr 1 .... e::ec (l.i.~) incLet> is recorrn1er.:.dcd with a ndrrinr.Jm

~ IJU e i:lg Of' B iX wh·~·t--;;··~·~ ~~~--t·~-l~·;· .. ~··:, ':.:·:~l~:·'·';·~·;;c; .. ··'~·;···· .. ~~,·:r~d:·~ i··~fl;~~::-~;~~~~ -----~·.-:!:""'""''~' .. """"·"=~"' .,,,,.,::;,.._

tl1e followirlg valueo for ti1e sl:in friction in pounds per :::;quare foct.

Intermediate valueu mn.y be interpolutod.

Depth (feet)

0

5 10

Skin Friction (poundo per square foot)

0

t~'()

tl:

If c:·:ct bea1·:i.ng piers are ~cs·i.r2:.J, :1 s;~fe tea.ri~,~ cnpaci·ty oi' ·three

tl;-:...·:.:~_;and f:i.v1.: hu.ndr·cd (3,~::.JC) poi..u1d:.-:1 per sc;,·J.arE: :·:.:.,ot r:~ay be U't.iJiz.f:d

R~ .':i ._;_5ptl1 nf' L(:n (JC.J) ~·c-c~t.

::\~ttJi::;nH:::-1t of JJicrs, pilEs, 02' cc:i...i.f-;so~s is r..ot e~cpected to be ~.:i~1if::'..cD.r1t.

Lateral lands w.ill be r·e~;:i.tJ"~.t7.':..l by the f.rictic;: bc-G1 .. icon tl10 f.Locr slabs

c"'.1!1..::!. the f;ubgi:-·adt~ u.n.d by th.c passive resist.:~1cc cf the soils agair1E.:>t

foctings. Pi. cucfficien""C :.:;f frictio11 of fou:r-t.e:·~tLs (o.4) n1'.iy Le ·LJ:~;cd -----"''•··-·-··· ,_, _ _,_, ___ , __ ,_,_ ... - .. ----·· ---~-betwee!l slabs a;id footi:-1.g~ and subgrade... The pas.si\re r·c;Jistance cf the

-~···-··-· -···-~·"-.

:;o:i.l r.iuy be tr,kcn to be -:::,;o hundred eighty (230) pounds per C'-ll,io i'oot

f lui~:;--equivalent •

. Active lateral $O:i.l p:;:·~:.~fJU.T'f: :3ho-J.ld 1)e taken t.s._ be thir-t;y .... fivo (j5) ..... ,~·---.,.-·-· .. · ··- . '' .. , .. ~ .. :.·.~,,.,., ''• ..... ,..,_. ..... ,_

pour,tls per cob) o font flt:id cquivaJ cnt. ~ ................. ~··

TitcGc active Gail prcssi_~_rcs rr:t1~·,t be ndjustf:d fo.:::· a sl.opir1g f3lu·cha:rge

if (:J.IJJJJ.ical.l.l.e.

-·

Dedp1 1cont'd) -·--- ~--­.. , . - ---- ·--·----~.

GE0-F:K7A Laboratories

Job Hurr.be1·: J.•c;....876N-79

J--.i.e to tL.e ex:par1s~-~-t. r1a.t:~~of the i'OUl1.~~-~-~t~·-· ~.e.~;,~ .. t it iG rccoITI!T.!e!ldf;d ··---~·,,···---

that the slabs on grade be reinforced with 6 :x 6 - 10/10 WWF or //3 barn at twenty-four (24) inchetl on center, Ttis should be tmder:Lain

by a niois·Lure 1)al·r·icr.

Co:itinuous footings should be reinforced with at least one (1) nu;:;1bcr

five (5) bar at the top,

'J.1he moi~1tu:re bri,r•r·icr ccnGiGts of six ( 6) incli.es of c1u::.:l1ed rue.~]-; or

clean ~:and. A six (6) r.ri.1 poly vi:··.yJ. et1loridc uheet, er· ccrnpar;'it:le

i..!npe1~v.i.Ollfi rnatcrial en ~op of i.t ffJf'iY be ut).l:,i.zecl [i,1..> ar.ld.~ti(,;·,~~ p:c-o~

tc~cticn. l\.ll J1.)i11ts $l1aJ.l lH~ rrJ.t.1.de sc u::..; to p1'-e.scrve tb.e ir;1pei·'v~oli.~·j

charac·ter. 'Ihe lnf;::m'brr,,.=1t·~ s!1oulcl be JJrotected f:rom p\trlcturc by a cu~;hior. c:f

.:::t loa:Jt ti...;o (2) ·.!.,nchc:~::. of E;ur1ci, above l~1id belo:~· t11e plastic s}-"(2·:.:..

T11e above c-:,·i tl:"l'ia r.1.ro ba:::ed on the asswnptio;~ that the rnois i..? . .;..:rc~ :..:0.1,:rier

is i11stalled ar1d the cc..:·:-~c)rete placed before the soil 11as heg ... rn ... ..:.c .:..:~~,.:\<]

0i5J:1.i .. ficalJt uu:rfacc cracks. .Should such c:racks ol:c.~ur, tl1e uoil s~-:..all tc

tJ-~0rouF):1ly wetted so tl1ut n.11 erack.s :have ctsappca.red r:u1cJ. the t:~c:_;Jt'...lrc

11a.s penetrated u nlj_nir.ru.m of twelve· (12) inches, 'lhe nloist·1.U'e ba.r-ricr

and the oonoretc its elf must be placed soon u:fter th:is wetting has been

acccmplished.

Den~cJ.~ t:l.o:n a:nd 1.r-r·cc ~t.~.~ova'.1

Special note shculd be taken <Jur:cng the demolition of the existine tree~

and retail1ing W(.l.]..l.t,; ~;a c.~> to locate all underg:rol.t.."'1.d i-Lerr.~it e.g.~ JJ.~1ic, ..._ ~ondi.li t, utct·nge t~nl~.s t septiQ tar..k.n, cesspocls or lcuchi:l.g lines, v..~ate·r

wells, :i.rr.i.e;at:1.or.l pipe, etc ..

P....."'1.y 2.eepat";e JJit or ccs~J~Jool fc1J.r.!.d ;;h~~ll te fU!i:~cd. dr-y and filled · .... ritii clea11

u.:,r1d.. Tl:.o top a::i_d f:i(ie::i ohall be~ br•okcn and :removed if t}:l=?Y r-:1.r~ w:..th;i.11 five

('.J) feet of finic;bcd-c;rade. /1ny 1'la'ter well d1a2-l be c\.lt off a'1d copped,

five ('.:.)) fE1 et l:JP.low f]J1ishcd grade ..

. -6-

p_~~o.!_~ticn an(1 _rr.1.:·.e~_ ~.:~c:_vul }_?.9Q.t-~.Q)

Gi'.O-m::'.l'A Laburatod es

,Jcb NUI'.lber: PG-i:/(6N-79

A':ly 'll<O'Ull pipe or tree root with a diameter rrcater than one (1) :.nch

sl"1all be excava:LecJ 1.l..r1c"i cleared fror:l tl1e site. ,t\r..y vitrified cl.:.-.y

lcac1·1ing lines lnay t)c bI'oh.cn in place,

All ca vi ties shall b" "Veed" S(l ·chat c<1tr:paction equipuent will not

br·idge durir1g rradil1g con.cluc.~tcd i11 the manner no-ti:::d 1)clow.

It i'l recommended that the demoli t:i.on be supervised so as to px·evcnt

debris from ren4B.ining Oll or 1Jeing buried on. tl1e site:.

~~r~a:~j,_l:~S

Pri:.:.r to the co1itrolled ,i:;l:'adi.ng operati0t.1.S, t.!-~e Co!ls-'::.r-;.J.ction are;i

s!Lo1lld be striPJ)ed c~f all veeeta.tiot1 and any o"t!-1er del(~te.r·:i .. ou.~, material

~.'.'"i~~t tn~'i~t l)c pt·cscnt.

~,!10 vet~e-i::.atior1 ar1d ether ~-~tr·ippi.r:t=;s st1ou:i.d '.:le .::·,;:;;:1cve.j fr·orn ti1e ~-;i T.e or·

~tcckpiled for late1' ~se 1;1 planter areas.

0.nly ~l rr:odcrnte amow1t of gI·r~ding is &1ticip,:;,teci. i~~ the developn~er:.t of

tr.e site, 'l'he following should be followed \o."hcrever applicable.

It itl recommended tlnt all areas at grade or cut "'co grade that will.

support floor sla.b::.; or nophalt p~fvi.ri& o:r that '..t'i..11 ::ceceive f'ill -~)e

scarj_i'j_ed t() a rnirli.Jnurn depth of eigh·t (8) inct.~s, i,..·atered ·Lo r~cnr

ci-;:;"tinrtJ.;:n nio;Lsti..trc content H,nd compacted to a roir~uro of ninety (90) per­

cer:t, of the compaot:i.on star,d.o.rd.

Where fill :i.fJ n'quired, it shall be placed i.'l eight (8) inch loose

layers and conlpn.ctcd at nca:r optiin1.un moistm'e ccnte:at ·to at 1.zaot

ni.nety ( 90) pc:rcer1t compactio~n.

M ..,.,. ~ c.d,, +-? -7-

c·r,u.dinj...- (cont, 'd) ---=-=~==8~...: ·::-=-

c;tocJi;:pilcd .fill so:Ll~

CcinpacLlon Stm1da1"'d: !1..~·;.'r.M. L 15;7-70, r.nodified to t~·: ... :ceo (_~) l.:.tycr'G

in lieu of f·i vc~ (5) layors.

GEQ.....ffi'1TA LJ.1Jc•ra~or::i E.'~=J or o"Lhe.I'.· apJ.;·:··ov{::d ~_;oilG c:-1cinee~s ,;~oi..:..ld tic

l'etair1ed to EUp~'!i:·v .i ~'~ all [rading G';1E:rc.-tion3.

be cor1trary to tl1e fjndi.:ng~·> 01·' t.i" ... i!::"'.i r~·.:;::·rt; tbi::.; o:·.i·::'...co::: 2~· ... c...:.~:..i ·: ... c

riot,if .. ~ed t.:io t:·iu.t r)rc)pc1-. rnodi.~··:',.c:~·-,.:..c-::.:.:. '.~.:·~y ::-e: 1:1..ud·~-~.

R1:-:por-t, t·cvicwcd 1:-y:

l)a'l e E. (~s::, P.E. C:i.v'i.l F.nc:,in('~c;r~ C-l~0.57

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GEO-EKTA Laborato~ies Job Numbor: FG876H79

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Plats

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RCBil·TC C~E,

Claesifieation lv1L .0rc.1h'".:! clayey i':iJ1e/ coarse S<"il~d:r silt,

r10C.e::.~a~el::/ rrio:~st, r.:1odcr...-:..telJt~ i':i..~m.

;~.Tl{ '!':::L:!i s:'..l-'.:J- i'ir18 s<::Ll:d, i~1c::..:.r.:.,r·~ ... te~ .. j r:·.ci~-':., :..oc.~,::rc1tr~ly fir-:::-:

Dopth of bag 1n1111p 1 e

Dapth of undisturbed cnmple

No recovery

Ground 1·rater

VERTICAL SCALE· l" = 3'

Per cont Moisture

,., .-, , .

Dry Density

)") • .11

~' 1 fJll" I

GEO-EKTA LABORATORIES

Job Number:

HORJNG 'niO Classification

Orn"'l-.::r-i, iO

IVJ.L Dr·uw.i1 clny~y f··'..:;.1e/ccE!.rsc fJc.u:i:.ly silt,, n1odcrately rno:iE;tt moG.eratcly fil"il1

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··1· -1 ·; j. i • . . ! ~ . i . -111 .•.

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Very firnl

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-j

0 Dopth of' bag sa.cple

O Depth of' undisturbed sample

0 No recovery

":J. Qround water .. VERTICAL SCALE l" = 5 I

Per cent Moieture

1006

Dry Density

105.2

106. 7

HlO. 4

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l~ORiJ~G 1Tt-l:Ri2: Claaaifieation

l\11.. Browr1 0·1\_j,yey fi11e/coa:rue sandy silt, t~iode;rately rn::iist, mode:rately firm

SM 'l\m silty :"'ir~e sand, moder~tely mo'j_E;t, rnodcrately fir'III.

_t.,1j_J'HI

Depth of bag sample

Depth of und1eturbed eacple

No recovery

GrolUld water

VERTICAL SCALE: l" • 3 I

Per cent Moisture

Platf: nnu

Dry Deneity

·o·, I I I ' 'i

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GEO-EKTA LABORATORIES

Job Number: FC:-87(,H-79

ML

SM

:·lCJJ{lJHJ 1•1(;lJH C1aeaif1cat1on R:rowr1 c]"-.1·ycy f~_ne/ccarsc oru ... dy oil-I::., modf~ratcly t:.cict, rnodcra.tcly firm

To.r1 tiilty .fir:c ~:>tJ..Pd, rr1oderatc ly rnoiut, rnodorately fir'fn

l~o i. uL

I~luck oilty ~~.s.~r, ::·,c<c:::'r~toly r..o:..sw, 1:1ocic1 en. 'le l.y fi~'r:;

Very firm

O Depth of bag sample

0 Depth of Wldiaturbed sample

0 No recovery

lJ c:,;roWld .water

VERTICAL SCALE l" __ J'

Per cent Moieturo

Dry Denoity

,, ~·

GEO-EKTA LAilORATORIES

/', /

25 ~I oj . /

,//

BORnJG F:i'!B Claeei:fic:ation

ML .dro'Wll clayey £ir.1.c/conrse sarldY silt, rnoder,a·tely rr:oist, rnodei-·atcJ y firm

S:'-1 Tari ~ilty f5.n?. ~tu1d, modcrntely muif.Jt, mocliJratcly f-i ~,rn

CL (J:rey:Lsl1 bl2ck fil1c .::.:.i..ndy clay~ t.!ci:=t, r:iodt::r·1Ytcly ·~·i~·':·::.

(J:::--eyisl1 blac.::,.: fi:-.~-~ 2,1il'..L":.y cl8y t :-:·ic:i...::.-:.~

r.ncc1 er ate 1:.- :!:~::'... r~~.

// ·1 )0 /. L...,(_)-L.U ~

0

0

0

Dopth of bag ct:n1ple

Depth o:f undisturbed ownplo

No recovery

'S2 Ground water .. VERTICAL SCALE l" _ 6•

Per cent Moisture

Plate "F 11

Dry Density

2000

1900

1800

1700

1600 f-.< Q Q 1500 Ii.

:~ 1400 < :::i ,:: i..')

lJOO ~·

~·:..:i 1200

Cl 1100 -~

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:t: 800

ts 700 ;e;

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() :e; 500 H

~ 400 LiJ ~. U) JOO

200 I/

100

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DIREC'.C $1-:~A~ TES'I'

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GE0-2J(TA LABORA1'0PIES

Job NumbeL': FG-876N-79

... ~

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SURCEAJIGE PnEssunE' POUNDS PEP SQUAnE FOOT

Plate "G"

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GEO-EKTA LA!.i()"IA'.:Onn:s

DIRECT SHE.AH TEST

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Job Number: Pc-li7CN-'/C)

SOEI~iO OllE A'.!' FOUR FEET

CONSOLIDATION TEST DATA

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,lob Number: FG-576N-7CJ

BGRING T ... ro fl.T T1i.!B Fi~2j.1

CONSOLIDATION TEST DATA

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G~C-EKTA Laboratories

Gcsa & Associates~ Inc.

LI'-1ITATIO'!S

1. Tf1is (~cotccl1r1ic~1l Rc1)o~t is -oased upon C.2,-:2 o~-0a."!..necl by st~r·facc

reconnaissarlce, tost borings, }.abaratcr·y ·Lest ~:~l!~~s, prclir;1j_nary

er1ginecring analysic, and the ~ecessary revie~ ~f ;eol.ogic maps and

literat1..<rc pertineut to che "ite. No i~lfcrer_:,o s'.-:J'_!ld be drawn L·or'I

the langua5c of the report t~a~ ~~e scope c~ c~e invesLigation wss any wirier. It muo;t be v·,der·o ':_.:>xi chat al t11ct;g-'.·: ~~:-ie observed r2nd

reported car.di tionc3 are r.oo•·>.'..dcrcd reprecsent 02c.'..-;c, local var:Letions

of geolog.ic .::1rld/o.r soil co::~C.:.."'.::io~~.::; :Jay cxi:::-t :::::~ -.-i~·Li.ch ·this i'i_r'L1

carYn<Yt a.s:::u.:'"":"'.E~ r·espor1{s5..bili·ty. 1.~~--iis r·epor·t v.•a:; r::~epar'ed upc)n yot~1,

request for our services, sr:d ir: accordance ~i:~ accepted standards

of profes~ional pr~cticc .

. ?.. Tl1is Y'C::'pC;rt .i.~; j_:~:~;.t(.\: ,,.,·:._-;:~-~ ~·.·-:.i "1_Jn1j.~}(':::t:·:~--~::.~·-:. -=~-_::"!.t i.t 1::, Ll":(:

r·e:)r)or1si-cil.i .. t~.r of t~t·1e ov·.,;:··:(!.:' ~--·.:· -:·:· ~·-... :'...:-:: r·£:~1:;~-,E::~::~.-~---=::,_-:.2..\-"e:. t(-:i er1;:~·1r'1·

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.i.rr:pl cr:1cLt ;:_·,c recorrir:iend:-, :. i

·to the works of man~ on ~~i5

char1ges ir1 a)pJ.icslil.c OI' ~ppr2~~i2te stan~2r~5 :::~:r, wh~ther· L~iE~Y

n;suJt L'On' legislation or· _-::e -,;~'oacier:i11g ~-.~' ;::::·.<'._.e:::,~;e, Acccr:iingly,

the fiwlings of this report ::-.e_y t•e ir:.vo.lida-:e;:'., .. ;,·:o:'..ly or part_i.HJ ly,

by changes outside of our ccLtrol, Therefore, -:~i~ report is sub­

ject to review and should :',(;'C -,.,<' relied, upc!', f'.:'.:-:c:·r 2 period of two

(2) year's.

Appe:1dix I

SOJL C!..'.SSIF'ICP_TION CHART

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f"';.oss & P.ssociates, I1·~c.

GEOLOGIC RECONNAISSANCE

LOT 9-B, BETWEEN AURA VISTA AND EL BONITn WAY MILLBRAE, CALit'OHNIA

September 4, 1979

For

Mr. James Ragni Millbrae, California

Prepared by

Perry R. Wood Engineering Geologist

Project 519-79

Mr. James Ragni 10 El Boni.ta Way

PERRY R. WOOD Engineering Geologist

1021 Dale Ava., Mountain View, Ca. 94040 Telephone (415) 968-2510

September 4, 1979

Project 519-79

Millbrae, California 94030

Dear Mr. Ragni;

With your authorization, I made a geologic reconnaissance of Lot 9 and vicinity to evaluate its geologic and seismic stability. I was present when five (5) power-auger borings were made to de­termine foundation conditions for a proposed residonce on Lot 9-B and I examined soil and rock materials exposed by the drilling process. Logs of the borings made at the time of my visit are included in a soils engineering report prepared by GEO-EKTA Laboratories, Inc., Fremont, California.

The results of my geologic investigation; analysis of bore hole information; and recommendations are outlined in the at­tached report. If you have any questions concerning my conclu­sions or recommendations, please contact me at the address given above.

Sincerely yours,

PRW/slm

At tachrm;nts

Geology • Groundwater • Wells • Home Siles • Soil·Percolation Tests

TABLE OF CONTENTS

Letter of Transmittal

GEOLOGIC RECONNAISSANCE LOT 9-B, BETWEEN AURA VISTA AND EL BONITA WAY MlLLBRAE, CALIFORNIA

INTRODUCTION Location Purpose Scope

SITE DESCRIPTION AND PLANNED DEVELOPMENT

GEOLOGY

SEISMICITY, FAULTS, AND OTHER HAZARDS

CONCLUSIONS AND RECOMMENDATIONS General Slope Stability Grading -- Cuts and Fills General Foundation Cor1ditions Drainage and Erosion

LIMITATIONS

REFERENCES

FIGURE l -SITE PLAN, LOT 9

Showing house location, bore hole locations and other features.

FIGURES 2-A and 2-D -Cross sections through Lot 9, Ragni Property,

Millbrae, California

FIGURE 3 -Geologic and topographic map of Lot 9 and

vicinity, Millbrae, California

iii

Page

l

l l l l

2

2

3

5 5 5 5 5 5

6

'I

8

9

10

Location

GEOLOGIC RECONNAISSANCE

LOT 9-B, BETWEEN AURA VISTA AND EL BONITA WAY MILLBRAE, CALIFORNIA

INTRODUCTION

Lot 9, Block 56, is located between Aura Vista and El Bonita Way, near llillcrest Boulevard in the City of Millbrae, San Mateo County, California.

Tho proposed building sitn (Lot 9-BI is located on the south (lower) part of Lot 9 (see f'igure 1 - Site Plan).

Purpose

The principle purpose of the reconnaissance was to evaluate the geologic and seismic stability of the Lot and to determine if the probable building site was free of faults, or earth ruptures.

The approximate location of the proposed house, access driveway and power-auger borings made during this investigation are shown on Figure 1.

Scope

The scope of my work included a brief geologic recon­naissance of the Lot and vicinity; a review of published geo­logic and soils reports; an examination of materials exposed ir1 borings made to determine building foundation conditions; and preparation of this report.

Tho scope of my work did not include recommendations pertaining to buildings or building foundations.

-1-

2

SITE DESCHIPTIDN AND PLANNED DEVELOPMENT

Lot 9 is located between Aura Vista and El Bonita Way in the City of Millbrae. The Lot has been divided into two parts (9-A and 9-BI. A residence, constructed many years ago, is located on the upper (north) part 19-A) with access from Cl Bonita Way. The lower (south) part 19-B) is the site of a pro­posed residence that would be accessible from Aura Vista. At present (19791 no structure is located 011 Lot 9-B. However, the area has been graded, several step-like terraces are held up by retaining walls, and an access driveway leads upward and north­eastward from Aura Vista. The terraces seemed to have been formed to provide level areas for fruit trees and vegetable gardens. Figure 1 (Site Plan) shows the location of retaining walls, access driveway, proposed dwelling location, and other features. Figure 2-B shows the step-like terraced surface. I was told that the retaining walls had been constructed many years ago and that the area had been graded to provide relatively flat surfaces for growing fruit and vegetables. Before construc­tion commences, most of the retaining walls will be removed and the area will be re-graded to conform to the new building plan.

GEOLOGY

Lot 9 and vicinity is underlain by fine grained sandstone and siltstone deposits of the Merced Formation. The Merced is underlain at depths ranging from about ten (10) feet to many tens of feet by deeply weathered, fractured, and faulted rocks of the Franciscan formation. Figure 3 shows the principle geo­logic and structural features of rock units in the area. The faults outlined on Figure 3 i11clude known and inferred segments of the Serra Fault, a potentially active thrust fault that has brought deeply weathered, intensely broken ancient rocks of the Franciscan Formation adjacent to much younger deposits of the Merced Formation. Also, deeply weathered, intensely broken arid altered Franciscan rocks probably constitute an uneven surface upon which the much younger Merced Formation was deposited. The Franciscan formation is not exposed on Lot 9, but Boring 4 (figure l and 2-A) tapped gray sandstone gravel and very hard sandstone about ten (10) feet below land surface and Boring 5 (Figure l and 2-A) tapped gray to dark-gray sandy clay about fifteen (151 feet below land surface. Boring 2 (Figure l and 2-A) did not reach Franciscan rocks at a depth of 25 feet below land surface, but that surface may be at a depth of about 30 feet. The weathered and broken character of the Franciscan rocks exposed by the auger borings suggest that the Merced was de­posited upon ar• old weathered Franciscan topographic surface. The absence of a line of spring seeps or other evidence of fault­ing suggests that no fault has offset the Franciscan bedrock under Lot g,

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There was no indication of surface instability on the Lot. The owner indicated that the retaining walls were constructed to provide terraces for fruit trees and gardens and that no slides had occurred in the twenty (20) or more years he has lived on the property. Hence, surface conditions suggest that the Merced Formation underlying the property is relatively stable. If local runoff is controlled and not allowed to erode gulleys, discharge into cracks or holes that can hold relatively large amounts of water arid overly saturate near-surface materials, soil slips should not be a problem.

If a residence is constructed on the property, most 01· the existing retaining walls will have to be removed. Provisions must be made to ensure that remaining retaining walls and cut slopes are left in a stable condition. Engineers and architect5 working on the project should seek the advice of the soils engi­neer as to retaining walls and stability of cut slopes.

SCISMICITY, FAULTS, AND OTHER HAZARDS

The San Francisco Bay Region is recognized by geologists and seismologists as being one of the most active seismic region3 in the United States. A number of the faults that transect the regior1 are known to be active and other faults are considered to be potentially active. In the 69-year period since 1810, eleven (111 to fifteen (151 earthquakes of magnitude 6 or greater have been generated by one or another of the active faults (California Division of Mines and Geology, 1972).

The nearest known active rupture is the San Andreas fault, which is about 0.8 mile southwest of the Lot. Greensfelder (19741 determined that this fault is capable of generating up to a mag­nitude 8.25 earthquake that would cause severe damage to utili­ties, roads, buildings, and topographic features.

A recent study by the U. S. Geological Survey (Borchardt and others, 19751 showed that Lot 9 is in an area where the in­tensity of seismic shaking (strong ground motions) caused by a major earthquake (magnitude 6.8 or greater) would be VERY STRONG to VIOLENT. Shaking from any one seismic event could last 20 to 30 seconds (Greensfelder, 1974).

The Hayward and Calaveras faults, both active and poten­tially dangerous faults, are located 171 and 271 miles, respec­tively, northeast of the Lot. Either of these faults probably can generate up to a magnitude 7.5 earthquake (Greensfelder, 1974). Because of the distance between either of these faults and Lot 9, damages cau5ed by a major earthquake would be much less than damages caused by an earthquake on the San Andr·eas fault, b1iL damage to utilities, roads, and building5 could be extensive.

Other active faults in the San Francisco Bay Region probably could generate earthquakes capable of causing minor to moderate damage to structures or facilities on or near Lot 9.

When or where the next major earthquake will occur in the San Francisco Bay Region is not known. However, it seems inevitable that structures built at this time (1979) will be affected by a major seismic event at some time during their economic life.

There is no direct evidence to suggest the presence of

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an active fault on the property. The California Division of Mines and Geology (1974) and Leighton and Associates and San Mateo County Planning Department (19761 indicate that a segment of the potentially active Serra Fault is about 400 feet scclth·Nc".t of the Lot.

Because of the nearness of, and known activity along, the San Andreas FaulL, strong to very strong ground motions should be anticipated and all habitable structures should be designed to withstand major earthquakes. Damages to buildings and building foundatioris can be diminished if steel reinforced concrete piers arid grade beams are used; if the structural frame­work of buildings is bolted or otherwise fixed to foundations; and if additional bracing is used in the building framework.

Seismically induced water waves and seiches arc not a threat to the Lot because the area is more than 300 feet above sea level.

Damages caused by flooding during periods of excessive rains will be minimal because the Lot is not on or near a stream or drainage course that is subject to flooding.

Landslides are not a problc;rrr at .Eesent 1 but in the fµture, grouna cracki"iilf-an<r1aria-s1Td'es ~cou~d become a pro12I~ alon~ the stee..P_siope a·e·ewC'en-l\ur--aTista and the proposed build­ing site. Selsm:rc--shaR1:Wg--g;:tl'ier<itea6y a maJOr ( magnl tuas-o:ti­

TQ 8) or great ( magnitude 8 or greater) earthquake on a nearby segment of the San Andreas fault or· movement on a segment of the potentially active Serra fault could disturb this slope, especi­ally if the area has been saturated by water from winter rains. For this reason, it is important that any water seepage areas encountered during construction be provided with drain pipes that will carry water by gravity flow to Aura Vista. Also, run­off from roadways, buildings, and other impervious surfaces should be directed to a drainage facility that will carry water to the street without causing erosion.

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CONCLUSIONS AND RECOMMENDATIONS

General

Based on the findings of this investigation, there are no uniqUE) geologic conditions or hazards on Lot 9-B that would restrict or 1reclude pruder1t development. The site is considered suitable for the proposed residence, provided that the informa­tion contained herein is incorporated in construction and develop­ment plans.

Slope Stabilitx

The overall geologic stability of the Lot seems to be good; no slumps or landslides are known to be present on the property. To preserve the natural stability, including any cut slopes for the access driveway and building pad, proper surface drainage should be provided and any permanent cut slopes should be graded in accordance with San Mateo Cour1ty and the City of Millbrae regulations.

GradinG -- Cuts and Fills

Grading should be restricted to that required to properly locate the residence and access driveway. A[l_y_~anen~ut_ slopes should bc kept at an inclination of"'"'2:1 (H:V) or flatter To-precTude- 6ccas ionar· ra veITing-8.nd-eros ion. AriYTi.lls, .. even_· for landscaping, should have a slope of no greater thiln---2--::c:-·- -Tn · orcrer ro -miYiITn1.--Z-iCerosFYi1;""- illrbare-slopes ·--snou1cr-bepiarited with erosion-resistant vegetation when construction is completed. Reliance on fill for support of any structure is not recommended.

General Foundation Conditions

The scope of this investigation did not include an evaluation of, or recommendations for, foundation supports. How­ever, observations of deposits exposed in power-auger borings suggest that the consolidated materials can safely support tho proposed residence.

Drainage and Erosion

Proper surfacedrainage will be important_i.n _pre.s.er:'.i.irig the overa11 stabilTt--y-of the Lot ;-Tnaevelopment of a general drainage plan, positive surf'acegradients should be provided to direct runoff from the roofs of buildings and impervious surfaces into suitable drainage facilities. No runoff from improved areas should be concentrated and discharged directly on the natural land slope. Under no circumstances should water be allowed to pond adjacent to building foundations or on the land surface.

G

LIMITATIONS

The opinioris, recommendations, and conclusions preser1ted in this report were made in accordance with generally accepted principles and practices in the field of engineering geology, and no other warranty is expressed or implied.

This report was prepared as an aid to the owner and others in designing the residence and appurtenant facilities. It is the owner's responsibility to ensure that the information and recom­mendations given in this report are incorporated in construction documents and that recommendations given herein are followed during construction.

As work advances on a project, unanticipated soil and bedrock conditions commonly are encountered. Because those un­anticipated conditions cannot be fully determined by collecting, describing, and interpreting soil and rock samples, or by in­terpreting information from exploratory borings and backhoe trenches, some contingency fund is recommended to accommodate any required extra costs.

REFERENCES

Borcherdt, R. D., and others, 1975, Prediction of Maximum Earth­quake Intensity in the San Francisco Bay Region, California, for Large Earthquakes of the San Andreas and Hayward Faults: U. s. Geological Survey, Misc. Field Studies Map MF-709, Scale 1:125,000.

Brabb, E. E., and Pampeyan, E. H., 1972, Preliminary Geologic Map of Sari Mateo County, California: U. S. Geological Survey, Misc. Field Studies Map MF-328, Scale 1:62,500.

Brown, R. D., Jr., and Lee. W. H. K., 1971, Active Faults and Preliminary Earthquake Epicenters (1969-1970) in the Southern Part of the San Francisco Bay Region: U. S. Geo­logical Survey, Misc. Field Studios Map MF-307, Scale 1:125,000.

Brown, R. D., Jr., Active Faults, Probable Active Faults, and Associated Fracture Zones, San Mateo County, California: U. S. Geological Survey, Misc. Field Studies Map MF-355, Scale 1:62,500.

California Division of Mines and Geology, 1972, Earthquake In­tensities: Seismic Safety Information Map 72-4.

California Division of Mines and Geology, 1974, Alquist-Priolo Act, Special Studies Zone Map, Montara Mountain Quadrangle, Scale 1:24,000.

Ellen, Stephen, and others, 1972, Descriptior1 of Geologic Map Units, San Mateo County, California: U. S. Geological Survey, Misc. Field Studies Map MF-328.

Greensfelder, R. W., 1974, Maximum Credible Rock Acceleration from Earthquakes in California: California Division of Mines and Geology, Map Sheet 23.

Lajoie, K. R., Helley, E. J., Nichols, D. R., and Burke, D. B., 1974, Geologic Map of Unconsolidated and Moderately Consoli­dated Deposits of San Mateo County, California: U. S. Geological Survey, Misc. Field Studies Map MF-575, Scale 1:24,000.

Leighton and Associates, and San Mateo County Planning Depart­ment, 1976, Geotechnical Hazard Synthesis Map for San Mateo County, California: Sheet 1, Scale 1:24,000 feet.

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Fll-;\11\E 3 - Pl\ELlMTNARY l~LOLCCJC Hlv' OF UlT 9 and VICINITY, AURA VISTA AREA· MILBRAE, CALlfOl\NJA

Colma fonnation 1md Alluvit"n, w1diviJed - Qllatcrnary Age.

EXPL<\NA TI ON

Gm logic Con1 '1c t, -.-... 3 pp HJ.\ i.n ,;1 t l'

QTm - ~lc:rced Fonnation - Pleistocene i!nd Pliocene age.

....... ...... Fall] t' SCf'lWTll 5 or

J\Jf - Franciscan Fonnation - Mesozoic :ige '- brJnchcs of Serra fault.

Sources: Topogr<lphy - ~!ontara MDlmtain Qt1:iclr;lnglc, 1: 24, 000 Geology - Bu111b Jnd himpeyan, J.972; Lajoie <LilO othns, 1974,

Faults - State of California S1>ecial Studics Zone, Alquist-Piolo Act, h.mtara ~!ountnin l)u;idritn.~le, 1~74