HomeMy WebLinkAbout6.0 General & Engineering Geology Report 01.13.1984Lincoln DeVore
1 o Box 1.1;'!
Glenwood ;il)nrn);; uukrr 1SIur)1
(303} 0d`: 6020
Mr. Dean Moffat
Sundesigns Architects
901 Blake Avenue
Glenwood Springs, CO 87601
Ia,
Dear Mr. Moffat:
January 13, I '.
GENERAL & ENGINEERING GEOLOGY
COTTONWOOD HOLLOW SUBDIVISION
GARFI E'LD COUNTY, COLORADO
Transmitted herewith is a report concerning the general and engineering
geology of a proposed subdivision located up Cattle Creek in Garfield
Co_lnty, Colorado. This report has been prepal.ed in accordance with
the provisions of Colorado Senate 13i11 ;#35 (30-28-133 C.R.S. )173 as
amended} and the Garfield County Subdivision Regulations.
Respectfully submitted,
LINCOLN-DeVORE TESTING LABORATORY, INC.
By:
Michael T. [,leaver
Professional Geolo..Iist
MTW;' d1
LDTL Job No. 5053N -GS
,Inrado Springs, Colorado Pur:krlo, Colorado
=rend Junction, Colcraa, Glenwood Sprruus, Colorado
nr1TRODUCT1O 1:
PcrSUM) el. or 1..inct,ln-1' err,,,-• :1r:•;i c•,•rrs•lr ter! •-1 <<QO10)(;i: invc _ti.;zti.t)n cif
the ]cral'ost•c1 lattont:•„trrl Itc.l 1'''.. ` ',ilcrliv15i+st,, I0r,11 r'C1 in (hr Northeast quarter
of the Sout:hwest quarter of Se".c t ir)n 12, ''.o;'In!Mtl' 7 South, R..inge 8E3 lest of
the 6th Principal Meridian, G irtiel,i C'cs•inty, Colnrarlo. rn ormation inc-luded
in this r'el)O1 t has 1),','r1 r econrlirissarlr„e, int.urE)rot..iticn
of aerial photiogt.-il h.;, I':a. i:• .1 icri of :our to ,t pits and re, -.e crc:h and analysis.
\ geologic vial is l-ro': idr i 1-i•;'.r,,2 1 csn:1 in engineering •ieo.locjy mal.: it
provided . r E' i';.)i o 2.
I t is oiil ii) : r • 1,;ll'1.1.Ili that t iii r to r'n :t °_ 1p';.icr :1n1 tt.c].y rc ,n'::re f::Ir h
are proposed on ?lu+ arrt' parcel. Two lots already have existing Le• identi{i1
structures on them. f:i iiv' !) i1 wells .In:1 ey tems are p>re;ic)f„r:cl
for the eleven ntt-
SITE DESCRIPTION:
The site is located ,ilc t, : ..'1t tle Cr,"ek, approximliely five miles c,'d_ t of
it's confluonL.e with the roughly ref tanrpul.ar. parcel
straddles both :.ides t the n 1c Ct c•d'F: Valley r:n l ] rev i'°}irr. land USQ has
been mainly iaimi nr; and ran,'list? t.
Topographial1y, the site i, ch,rrac•teri: eri by moderately sleep ::lops
descending to an dist-t,'cst t tr n lino valley incised thrc,u.:=rh an upland mr::,I.
Elevations on the site r.ui';c• 1:c ri ipcl ro:-:im.ltely (11-.20 to Jbciut (900 feel,
Slopes on the site v it 'co; side_'). ibly with ,l t=1a s.,rity c-.•r)r -10%. Slopes across
the bui ldinit sites I di neje lie:,.'1 101. and 50%.
'rhr M. -00r dr.linago eat I:: I:. Cal t 1f_ C oek, ':liu n cut i across thr sit
rails cast to wrst. I !! 1"Iv 1 :I c1l.• 'Il d1ri jr. '1 111y runs into Catt1r4
Creek from i.lie south and 1iiu 4th diveitr_-:E sntri .1 small bond near: the
center c:f the sit-.,. :,11. t:ie ::i1..: dEialn!';t! i.:; isltlrNst:Oly tributary to tht
TZOai in'; Fork and color..r'ire !ilk'' r
CE 1EP.ii1, CE?OE,Ut;1' :
The pro; osed Cottonwood in a geologic Getting
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GENERAL GEOLOGY, , C0i•1'I(
characterized by a sequrrnco r.;" rt•l,rLively ytaur;cl, laar:,alt lava flows overlying
a thick interval ttl rel.itivi ly old evipnrite if.t1:s. The combination of the
resistant b:lt.,.;it c:.ap and the eua..l, rlyincl body of rsoft, easily eroded ciylmsilln
has resulted in t 1u: rife'. - lc'.l:tlf rli .iI many illi er eE,L i nci .'.trilctural features,
including some ar•::as of 1.rnsl:.l 1 '.L:t;, unstable ::lopes, 1rotenl i.al.ly trustable
slopes and rockfalls. in Ir•rri• recent timc s, the site has boon subjected to
various surficial 1 roc•csse• primarily involving the weathering, 1:reak-urs and
erosion of the bisalt.
The primary hell:crck I ,:t tt is rh itnder'lyin.: the •:ito is the Eagle Valley
Evaporite (Pev) of Middle 1 l rlii. '.'1v.ini in Ago (Deposited about 295 to 280
million years before the 1 to ( 1:t) . As the name implies, the Eagle Valley
E?vaporiLe consists of quantities of gypsum, anhydrite and halite (rock salt),
together with layers ut mud..itones .and Simi l,tr Locks. The material was
dein.:asited .it ,t Lilne in r'hhc-il I.ar:;t of c:rntral Colorado—the Eagle Idisin--ws
c0vc•re::1 1>y a ti.h,t1.hw :;t.l, •::,sll Hirlltland; 10 rho northeast and southwest, and
an which an .arid or stmt.-.ar i.i . ] ;r,+ ttc• pi eva l 1 E'd. With the passage ai tlu.¢?,
the Eagle i3ar.in deeper ed ,o; ; ; rlt ::i both to Lon.ic forces and local subsi-
dence of the crust under `he loll of accumulating evaporitic _,eciiment5. As
a Consequence, a c•un:;ide:.tt?lt original thi.:kne';:. of the Eagle Valley i v.alorite
was deposited. Outcrops of 1:.t 1] Volley E vai ni ite can be readily r •cognized
throughout the lower Rd ring Fr:ri: Valley by the characteristic gray, yellow -
gray and gray -black color c:I the 1.(.11s, ail i by the contorted, eroded topography.
Outcrops within the 1 rol0 e.: .:11hiliV1,;ion ,Are found along the slopes south of.
Cattle Creek (see i'ic)ute 1) .
with the ••uttincl of tip,- ktr,,n lnl Fort. Paver Villcy, thl Eagle Valley E:vaporite
was on:::e again e%posed at li,t• giourd . tirt,1ce. 1n general, evaporite rocks are
subject Lt: 1ala7.:o_ic• t to !Andel 1= A.
As long ,a• the Eagle Valley Ev,iporiLe
was confined under the fairly uniform loading of this}: sedimentary rock beds,
it was unable to deform oul:i I 1 r.•: appreciably. When Lhe volley cutting unloaded
GENERAL GEOLOGY, G' , co:.i.
a part of the Eagle Valle.; :',t':Il Or•1te, llowe'v4't , thc^ rock:; lac-•j<in tc squeeze out
from beneath the heavy lull :1 i mount sin.; lr; l l<?1:1y 11r:iw outwards toward thc:
valley. This l;rvae"e;;.'; war; ll by (Thom t..•11 1G,Y:r1ei; pn 1he rocks which f_:1tts4:d
them to e:•;pand in volume.
Consic?erabl e vol c 111 t
.t;:ti'.'ity .11•;o 1.1)4.}', ',Lice in Ulf! Roaring Fork River
Val ley at about r,4'. Art i;'4' vesl' .11i!;111 had :seen present i.n the area
since about 2,1 million ye,1! Lee fore the pie.;erit; most c r the activity i.n the
immediate area 01 the plolys:-ecl :; llxlivision h�,tre•v4 r, much younger.. About
11 mill ion year..; l;a::1 ore t he i •rc•scnt , a soy ie'' 4)t et ul'tions of hasa.l t and ash
rapidly built thc: chieId vol•_11i1 now i:no'.:n as P.'as4i1e 1-kruntain (summit about
9 mi les east of t hc- ; i t c.) . 'Phis .14 t- ivi t . t•, I 01 lowed about one.-hc:I f mi lien
years later by allclth4:r r 1 01 b1 is ,r1. L lava 1 1(1'.,;;; (Tb) , which poured out onto
the f loor of the vat ley, 1t'o.l creotf d the Ill land mesa now known as the Mis otu i.
3lei9hts care.:. 'Thus( ¢ l t:: t4:sL ditc•rt1y upon :lir hackle Val ley E',v;lpor.ito-
Si nce the format inn i t 114 :i.a s,1.I t , 4r! out, :\6.1r [ I ,=]:51 iv! throu4i11 the can ie.
1oe4::: hcu; di';:11.....1ve el t h4. 1 11114• \7.:1 1 .' 1::.=1„ r t t 4 a1 Ilii' 4.4,111 .4r1 w1 1.11 t 110 11,= „11t.
Cclnsc. luucntly, the 1:.1.;,!1t h 1 r;1:1} ,i.icrcl cit1" hi. :101ut inrt a2.0,1r;, and m.lrked
disruptions of the stir t. e toi 1') tphy ,and r,1 :lin inttclrity of the basalt fl:;;,/s
have ocurrcd.
I'hc
geologic strur.:ttirs• cc: t he ,'lren i;; c1. srninated by regional feattn: es re-
la ted to the uplift itur Subfiequetr defc-rmaLI.on at the Southern Rocky t1 .;.::,tains.
`1'o the west and south::": .I are thr sr.a:f 1 x•11;1 cit the Ca -and liorlhcack, which
marks the boiindar 1.;c t::cc`r t he r•c lull lots .11111 t 114• .tdj,lc.cnt Colorado Plateau, iiid
the lata:;t-I,arami de 1.1114'111, iralrtr;. !. r• the :;rlurrt :-opti5 1accolitit. To thr.
0 1st ,1nd southeast, 11 ;.= tin: .l t;-!, .411. hi t 1;1 .n 1'•: 111,• Ford Ic 1•Ioi:11t:lin and
Castle Creel: Caul ...t ` , :•:111411 • .",nt rcll 111. 4111 :4 4i :Site Poarin(I 'or} River and
tn4IV}: the flank 01 i -a: al: '�411;41,:tt1. The rain Lr.l.,.c: of the 1'ed Ta1:1e Mountain
fault classes :trout f, :°11] to tiut 411 th4' pi4ri,W.c•:l :;uhclivinion . Tt i:,
probable that the .v,llc.,lt,irc-t i -,'i [ y' which fottnc.;l both Ba,alt Mountain and the
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GENERAL GEOLOGY, (7.o:';'
Missouri heights Li t(.l-: r• 1.g'.vl to 111.7' two fault rystrun:-., which !rear.. with
each oth421- in the Pa,7a11-11 1 .sre:. :n ,:rut(_lnj °.s �'i'1!'1 1Sl the f•11r?r')uri.
Sleights dist 'Act itsr 1F. it l:>r.• r, lhir i�; E�rnl).11:ly clue to the mec:harsictll in-
competence. c;] the under 1 ;'r; -: 1. •j1+. V,ll 1' y i"v,!I r-. t t r•, whir h t(n1 i_. Lo flow rather
than break undo! : t
DESCJI PTIt".1i Or MAP ti';l'1
The f c.l 1 owi n'; i.':.r l i ! t i „r: r . k l';+.•+l upon visual examination o E the geologic
units mapped. The location r:; ! h('$ L units can be 1 our,rl c.r; the geologic m-41 ,
Figure 1.
EAGLE VALLEY EV;lM.Pi i I: I -'fl •1A'E"< li l!
'I'he dojos 1 t ;. ::.1 tha; :,I ta' i:. un, ie i 1.1l!1 by t he I`( nrssy1vanian !r(1c: Eagle
Va1.1ov F voix,ri I r wi1ik ia, Ott t hit, :.^4 1 •lc<' i••
lmj,(: ;ed (.1 massive, coarse to
fine grained, tit h i Lc tR ` I [. r'' ,!7p. um 1J('af', d nd w i de 1 y spaced beds 0 1 calcareous
sandstone and i.:t}: ,;r.1;' t;'.;.11" r•:h,l]' '1'llts unit is ;o1uble, .1.Ilr(rrflil'I+mt;
111x1 prone t(' r°;trrtl <1 ttkl. t Irl;. i:
DESCRIPTION or MAP U ,
TALUS DEPOSITS ()L1),,
as observed in Test 111 Pl. Tilt .4-, ibic' to pciL f•thf L
ro,Afall ha;:ard-: aWi .11: ..011-;id,"Yed pr.senti;glly nn: -;table. Construction
on 1 1t:•s 14 'hijl 1, i40.1-(1,11. by .14,1Ailled '11r. f4,1,::4iric !-ItUdiP!".; ro
delerminv petpp,r trtp,r 1 Cur.i e Vein. al a minimum ,o4id
drainage should carerully controlled.
TERRACE GRAVELS (pi)
Sttam or tivor trr.).A lrAvois Lon 5n ourill in (he .iouLh
portior of the 17it4.
dopc!:its ch1racteri'5tically consist of a
mixture of Sl11C1 1 t gravel and c.!bblc, with the particles bein9 -
rounded to well -rouh,iod, Arl .4,1; on.cuntor..1 4n le5A Pit fri„
LANDSLIDES (;lr.)
Two landslides ..-:tee :.onnd on the !..ito, one on the eastern ethic and
one on the wesrein cf the sire. The Lirr!,.-;lides are approx,imately
several hundrod year:, ,11 cd h,ive 1,-:111t,r,i from rhc failure of surfirial
mat ori a 1! .1r, 1 'Jr 1.11.. A.1.11 i ;v. t r! I1I Vomit (414 r (1U,: IP
tkiratiOn 1 1011 . t t he sl.'; -pr. Th.1.7: 11C
unstable and shoulii be ,tvi.iOnd. No construction is planned or or near
these deposits.
DEURIS FAN (Odi)
A small d(-..bri!, 1 an wa,; nri-)unt.ered near t he center of the site on the
south sia,or c. -it fan a minor deroitiorial fe-iture whin
does not pose • siqnif i c•Ant h mud I r:r 1 1ndin'i. 1Jrconntruction
is planned on or near
COLLUVIUM (Qc)
ColJuVium mItert 0 rh.1,)sited by the actions or sheet-
wa-111, erosion anA 1 r No(Ter (11 colluvlum are indirdied
1:11 the Toologic m-rp .)11 111,' southern portion of the siLe and are found
as wed9e-sharei deiTrt: o the 1:,.154ij of the slopes and in the bottom of the
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DESCRIPTION PTION OF MAP [1:;,
COI.LUVILItI (9o), ('On.
dr.-ainacjeways.
These cv11,1:1.11 c1 1t);;lt': ['1)11':1°:1 Of d 1l1::tlll:e of .1r1:1, 5Ll.t,
C1.iy .and gravel rl,: t i ve'd 1 r can t h,. l•:eat Il r i n<i r)1 the various other geologic
[;nits present o11 the • Itr. '1'yl,iv:,tl ly, thctar rinl r}sltF: e?e Eine-•;rained
in nature. i4 . I1 ;htii -.,unit', fine, ;i 1Ly c:l°ly w<v t:rs n•;,ntered in T»st
Pi t fl2 to a de; t it 111 lc} r r t . C'ol 1. 1Iv 1-s1 rl:rmr
1 t 1 1 1 1 hav(_: v3rial:1.e
thicknesses 01, the si tc , tic; ending ()11 ktci r 1c)C t ion :incl size r;f their
,-1k! 11".11111.1 n ar'A0l t I+:; 111 1T)e -/f an
t.tnatak lc an:1
site spec- i1i, °:t.•'11I
ALI,UVIUt',I Wail
$ 1 'JIM tr.> rr,n• trncl.[.1111 oil thrs:{-
1?Cent all Ivil.srl de! 0si tcci along :'rrLl le {'rer i.: consists of. low elr n..:ity,
line tjralllC(1 rill[:,, SLi li .111rt cl.lys r1Vt I1yi!H1 lIIriCif.r.ltely r1erlSc', Silt
sandy rtI aye] S 1.111 11 01'('.1:,1r)t .11 1)0111(1t ! : l'llo'.o 111 Iii't ::,oft clays wc!rr) on-
counter- 1 to ! :Jittl: 01 n !t'tt in '14' 1 lit 1. 1I;oCie deposits ,ire Chr1I.-
neter-t.,ed l)y h) 111 1[14,1 11 t lrlr'turlti'?ns.
12!-1CI Idf ER1 rIC 1 !.01.c)C;Y :
Geologic fact which 11( 1 iku1',• t.e) ;$1 tect. carvel.•;)rr,:nt .lr c1rIencle'nt Ipork
several factors incluiillrl: 14)10.1r-.ii)hy, :;tJ1:lace and --;11b:;lirf,lce_ drai.n.ule ct,ndit-irons,
en<ji.neer.incF of the imiteri.i1 types and Clio development which is proposed.
The severity of each typo of will depend on tho nature of the hazard arv.l
the nature of the pl. 14•secl ti• 0.(01 i':grit. The fol di :;_llSsl 1 cic .crihe the
geologic hazards m.iplserl 011 1•'itjur.--' 2.
'.111,01 t.°t°Ak t i.1 `1"-:"
Stal,i 1 is y . f 1,: I h 11.11 .11 i t l ,i,r0 , Ind k.11. air.1 i i 11 slopes i:: , facl:clr
t1: r,rl,Q_.i�ltr. A11h• ingli , 1• n, � I �IrOvi ,c•.Itc'rl rust:�thi].i.tir;: •1F the hed-
Lock units found .on the- :;I.t. lel 1110 1c:I1n :)f landslides indicates unstable
slopes are i l=:`(!r r rttw r ILLr41,-1 jou !C-':1':'Lt:LC. h.1L'e boon planned on or [)fll;
the affected slt•l.•o° .a;5,1 .a..iiw15n4t is the br'•;t mitigation for these areas.
ENGINEERING GEOLOGY, F'1'..
SLOPE STABILITY, CONT.
The areas o1 active 1.1n®islr:ll.ng have ler-re indicsated as atr::.tattle or .land-
slide on Figure 2.
Other slope: cn the site have been mapped as potentially unstable.
These slopes, althcuyh in a relatively st ib/e :.ondition at present., could
become unstable depending on proximity and inappropriate development,
grading and changes in moisture conditi ncc. Presently, most of these
slopes are dry and tllr'retorc, arc: not of a major concern. Depending on
proposed dew, 1c.pr.. itt., t:nciJntrnl lLcl ,trl.i1 tion
of w.ltez to these slopes,
they could 14...imo len ;t,,l,', .111,1 ,r, 1 eve 1;erl.k,1 e.liny etr+1l(1 ru:sult. rt,utur.11ly,
it. is wise t(; _IVC) t.: the 1�,k e:i ii 4 i 1'Y. rI1.5C;ll.l.tive or urlresLi cted
.Jevu1.,1,rncnt. 11ow,•vt t, It:Vt•l:.i uu r!t nrry !)t .1f:l:r411 ::i,tt1. i f precede.] by a
thorough site in-.e;tiyatiore, so that stable construction -_.an proceed.
flOCKFV\LL IIe'1ZN D
k?ocktall 1i t:.'si, ,.. : :nge l:r(:,m minor to moderate on the site. The main
area posessinq rs rockfal1 hazard is :re tkt, northerly portion of the site
at tate base 0t. the .,,t+'r. rr ;lope desccndinu from the mosa top. In thew
areas, blocks of h•.;;alt weather out of the lava flow which cap the rreesa
top.
1it:ic Li on of the hazard on this :,ite appears relatively simple in
most cases. !•UtigAion could conFi.st of simply taking off or pullin(r down
loose and perche:i boulders from above the building sites, or by providing
sere sort of catchment, armament, or deflection structures where necessary.
The best method can kph dotyiminod in the pr.elirninaty design stages nnre the
site_ and type struc t 11. h(.en piec.ir,ely located.
FLOODING A1'1D St11:1 :1c'L Ue?It 111i,;) :
Due to its tremendous cu: u-ity for damage, flooding must he considered as
a potential ha::ard affectimj tl,, portions of the site adjacent t.o the major. and
FLOODIN6 ?1'1I) SURFACL
minor drainagew.-kys. p halt a dot a I f 1 oorl plain and
drainage study i ht -t ngp 1.d ..fl by a •i 1t 1 I enc.; i neer flonar 1 ly, the
best mi +la t . -1 : ' 1 1. t d 1'; r:1-111111.3.1 ILI on
or the t 1,4 01 II m!. ,•,i11, .11 Q., •.; II•r 1;41 'Hi ILO this
hazard.
E.:1V RC.N•lEfll'A I, HAEARI) :
A certain derin • ( t ! i • thrown:, Alt- •del,tern Colorado. Al though
the R.7.7.-1 ri ForY. Rivat ey 1 r.u1 :1 CO. i ...31 1 h tikc Lvit y on the same
scale as some pa rtf:, 1 h.• ti; 11 y 1 .- 1 42' t "0; :lig f sijru f irant na'j i.tudo
have 1)0011 fel t. ill th i arca wi thin ! e, df..d h I y. act iv 1. ty seems to
be concentrated along,-.-•. 1 (*.ritent!• t he Cast I.• Fan 1 t zone in the Aspen arel
and in he Whi te River 1m1 1 t he not LI) I en...:o4-xl Springs. Al though the
Red Table iouritain F tult tic,(-•.. n.)1 ::ecm ti, be r...n 1 ar 1 y active at the pres'ent
time, the poten 1 [O 1110Veiii1::111 1 1 1_ app,ars that there is •i chance
that earth tremors of Nodi i :101 1 1 i ntenity VI or VI :I i ma Le 1 y
Richt et magn it ark. • 1 11 thin he 1 1 t' r1 t he cicL.velopment
Accord' i y , i1 1:, -trti•il: 1 yc, 111.11 "1, I -Oil wi 111 I Ihe ]Lr)] osecl
subdivision be de!--.i.uni(:,1 ik•c(y....::.ant.c. WI 1 h 1 ho the Lln.i form IluiLding
Code for se ismi c
There do rif.::t ape -r to bt• any Jot o.7.; tts o rad loaLL ive minerals or otfler
S01,11 COF 1 aticmia I cr.'s rad a 1 1 t y 1.111‘r (11 I )1' itti 1.,. proposed c -:b11
Furtliet more, there not elI1i 1 t: •)nom 1 1 y extractable mineral
deposits eithor on or nelr the to erty.
Although sand and gravel forms 0
component of the stir_ 1 lei .0i I r mei enormous i!natit i L i of gyp!7.7u1fl are found
within t. he E t le Vt 1 ley i vai 4:1 11,121 [1101 1 hose mi nera 1 deposi t s is of
quality suitable for •t 11 OL use.
SIMMARY :
The lollcwitol sioratiary L. fd 1he hazarLts associated with each
SUMMARY , CONT.:
lots' building envelope ar:;i
'.: Le Ti t.i.,iLton it? chnigthe s:
Lot No. 1 is to.iLOC: uta t.alu:; air.lsorit:; iloci may Le t.tvr;cep tiblc Lo instabilities
or settlement i f arol,c.r ii _;iyn techniques ale not f2mployecl. ii Subsurface Soils
Explora tion to es tab! ish Lur:n._kita on des i lri soil par.ame L r+; and prop^_, dra :i,z,yn
measures will be ner'' to ru.tr. to t iu i oLe ntial lha:.arra.
Lot No. 2 is a the roc of the t.a1u:. doo1>ot.its and o Subsurfa..0 :;oils Explora-
tion will be neceasa ry to prey] dc- foundaLiran design. The cri.feria buildi . f
envelope on Lot No. 2 i..; also in a rock fall haz..rrd area ,:,nd the presence of
several large boulders in.lic.ites ,a model at.c;l.y :,eve re hazard may exist. ft site
specific investigation i.s recommended to determine the severity of the hazard
and moat effective rni,Li a Lior,. tie presence of the county road above the site
may be used t.a advvintage an toppiny ros r•)cl:_; or at lea_ t removing most o f the
momentum of the larger boutde.:-s...
Lot No. 3 ti -s hc,en placed in thi a11uvium olony Cattl^ Creek and indications
from the soil:: exposed in '1'c:; t. 1 i.t - E are that s1a4a1loy:: foundations mr.y be suitable
for foundation!; on t h i:. lc: L. A Iiia t.iilrl.11 Stil);;lrl I 1'::171orwiii.on will be
required to es tab 1isit appropri a to design 1,u:mete rs on Lot 1.1o. 3. :surface boul-
ders indicate rock fai 1 tray <LIF.o affect this site and should be addressed. The
flatness of the site, the set back from the toe of the slope and the presence of
the county road may aIready effectively mi tigate the rock fall hazard.
Lot 11o. 4 alrccr.l• hail ,:n c..;;istiny ;.La.ucture built on it and is not addressed
in this report.
Lots No. 5 and :o. 6 arc: Io •.1 ted on p...aten Li4111y tin:, table talus depof;i tf.3. A
de tailed Subsist face Soils L :u1oiiLion and a buii.diny and foundation proper design
should mi tiyate nrol loms for cons Li uction.
The building etwelopt:. on Lot N. 7 I i i n an .apparent hazard free .one and con-
s truction
on-str'ucli-Un should rant eraa,c",arn.t r ,any yt:ulogic- hazard:;. However, a Subsurface Soils
Exploration to establish prc!p( r foundation design criteria and drainage control
is recorru;tended.
-9-
SUMMARY, CONT.:
Lot No. 3 has .r to i hui 1 dins, envelope located on top of a long, narrow ridge,
which may not have any :.Mar f wont her::,ltd:: ,.r;soci:rtod tri th it, provided a proper
ret back is main t.a.ined ft.orn the poten Ii.a1.iy urt:;table slops. A site specific
inves Liya lion i:; r common de t to de t:c: rmi ne how close to the s lopes cons Lx.ucti-on
can be safely accomplished. 'Phe dense terrace gravels encountered in Test Pit
41 should provide adequate bear in for conventional shallow foundations.
Logs tao. 9 and No. 16 are both Located on coL1uvial slope wash clays, as
indicated in 'Test Pit. c: Z. Foundations may need to be designed to overcome the
expansive properties of t e;—e clays and site specific investigations are
recommended to deLer.mine propel design criteria for both foundations and otiter
Structures such as retaining walls, pavements, etc.
Lot No. 11 has on 0x.is t i nej .. t.r'uciur e and will not be addressed in tiei
report.
Lots No. 12 and No. 13 rose the more serious con:. Lr.ucLion problems in this
subdivision and :dill requite dci ailed site specific investigations to overcome
the f-:otent ia1ly trns,tahLe .nl,e.: and rockfa11 IL1zarcl. ,1 hi 11.si-:1n torraced type
of architectural solution may be appropriate in cicveloning these sites. Possible
mitigation recommendations may include, but are not limited to: shallow cuts,
terraced box -like const:.ur.-tion, heavily reinforced foundations, elimination of
uphill doors and windows, deflection berms or walls, special drainage precautions
and special septic disposal construction to eliminate introduction of water to
the subsurface.
We hope this has provided you wi th the infor.ma1lon you require at this
time. If questions :;houle: art ;e, please do not hesitate to contact our office:
at your convenience.