431 "lo. Suc:hanan Clrels, 11& •Pacheco, Ca. 94553• (415) 825-3311

Henderson & Sons Construction Co . . 344 Westline Drive #107 Alameda, Ca. 94501

Subject: Seismic Refraction Data Kerrigan Drive Oakland, California

Gentlemen:

January 26, 1979 File. No. 4250-1

This memorandum summarizes the results of our seismic refraction

tests conducted at the above site on January 23, 1979.

Two lines were ran on the north side of the structure with a

signal enhancement seismograph utilizing an eight (8) pound

• hammer as an energy source. Seismic Line S-1 was ran nearly

parallel to the structure and Line S-2 was sub-parallel to S-1

on the adjoining property, (See Sketch). Data from these two

lines is discussed individually below.

•

Line S-1 - Soils or fill in the seismic velocity range of 1,100

feet/second were located on this line from five to eight feet in

thickness. High velocity bedrock (15,000 feet/second) occurs at

a depth of approximately 36 feet at the east end of the line. A

high velocity.rock zone was also found near the west end of the

line.

This feature is interpreted as being a near surface layer of high

velocity bedrock. It is not considered a significant geologic

feature since the velocities on either side of the high velocity

zone are nearly equal.

Line S-2 - Seismic data on this line was consistent and high velocity

-1-

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Henderson & Sons Construction Co. Page Two

Seismic Refraction Data Oakland, California

bedrock (12,000) feet/second at a depth of about 34 feet was

found on the east end of the line. This is considered consistent

with the bedrock data on the east end of Line s-1. Velocities

of the soil or overburden materials showed good correlation on

both lines.

An anomaly was found near the center

step

This

between rock with velocities of

of line S-2 which shows as a

3,600 and 4,800 feet/second.

could be interpreted as a fault or the profile crossed a

thin, near surface low velocity layer between 50 and 60 feet. A

large manhole was located 15 feet north of this portion of the

line.

The anomalous feature on this line is considered as being a bedrock

irregularity possibly due to weathering or erosion. These seismic

velocities fall in the medium range which are characteristic of

weathered or soft rock. Another factor in our analysis is the

proximity of the manhole to Line S-2. Excavation and backfilling

around the manhole could also have an effect in producing the

anomaly.

SUMMARY

Since the geologic structural trend in the area has a northwest

southeast trend any fault related feature should have been crossed

by our two seismic lines. The anomaly on Line S-2 was not en­

countered on Line S-1. Therefore, it is not continuous across the

site and is interpreted as being non-fault related •

-2-

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Scale: 1 inch equals approximately: 20 feet.

SEISMIC LI NE LO CAT IO.'lS . '

Kerrigan Drive, Oak1and,Ca.

CONSUL TING QUALITY CONTROL ENGINEERS FILE

4250-1 FIGURE

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1

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Henderson & Sons Construction co . Page Three

Seismic Refraction Data Oakland, California

LIMITATIONS

The conclusions and recommendations contained herein are pro­

fessional opinions based on generally accepted practices and

principles of engineering geology. This report is subject to

review by the City of Oakland and there is no guarantee that a

building permit will be issued based on the data contained herein.

This warranty is in lieu of all other warranties either expressed

or implied pertaining to this particular project.

AB:HWS:dg cc: 3

very truly yours,

CONSULTING QUALITY CONTROL ENGINEERS

tf/rrl'l ~ Alexander Buller, P.E. Civil Engineer #19648

"JJ. V-'. ~ H.W. Short, E.G. Engineering Geologist ~130

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SEISMIC REFRACTION PROFILE . Kerrigan Drive, Oakland

CONSUL TING OUALJTY CONTROL ENGlNEERS FILE 4250-1 FIGURE S-2

CITJl •CE:

431 No. auc;:hanan Circle1 116 •Pacheco. C1;1. 94553 • (416) 825-33'i1

•

•

February 5, 1979 File No. 4250-1

Henderson & Sons Construction Co. 344 Westline Drive #107 -~ Alameda, Ca. 94501 .. __

su~~: - L~r-~i~Y;~-;~-if~=~=~ Oakland, Cali -rri"a

~~t*~~ ~/M,~~~

Gentlemen: r ~:£1 '~r;K'" At your request, we are sending the logs of drilledJ;:st~

in-place concrete pier excavations. The three logs attached presen~ typical conditions encountered during the drilling }iqf1f operat~ons. .z.,

As indicated, the piers are bottomed in shale rock at the northerly end, serpe~tine in the center and sandstone at the southerly end. \

I

We trust this provid~ the information requested.

AB:dg cc: 2

Very truly yours,

CONSULTING QUALITY CONTROL ENGINEERS

d,iJ . / ,ll'--//:ly/...n'- ~-/71 Alexander Buller Civil Engineer

, .. ·

•

••

CONSUL TING QUALITY CONTROL ENGINEERS

'4:n Ng, B1.1et'ltina~ (:Ire!&,# 16 • PachK.o, Cil. ~5.5a • (416) 825-.3311

Lot 182 Kerrigan or. 4250-1 7-7-78 Job.No, Drilling ·Date-------------

' S<1rnple i D~plh

(ft)

Blow-i; I

l)E."f I fc~Qt ~

I --;-

I

[.

I I

I i

Mojst1,.1r'1:1 I Dry U1,lt Content WQ"ight

(%) (!)Cf)

Depth {ft)

l~

3_

4~

Driving Weight Drop l-lmigtu

BORING LOG (Drilled Piers - typical north side)

DCSCFllPTION

Log Surfac~ Cleared ground

Brown CLAYEY SILT (ML) firm, damp

5 /"' Gray SHALE - firm, damp

.._/

6~

7,_ (grading harder below 6 foot depth)

s_ ---- -i.- -- --

'-

I_

L I

f­L

No free water encountered. Bottom varied from eight to nine feet in depth.

PLl\Tlb 1

CONSULTING QUALITY CONTROL ENGINEERS

431 No. Bue:h1111n1111'1 Clrel1111, #15 • Pilcheco, Ca. 945SJ • (415) 825-3311

Lot 182, Kerrigan Dr. 4250-1 July 7, 8, 1978 Orilling Date-------------Job.No.

Elevation------------- Dl'ivil'lg Weight 0fOP Height

BORING LOG (Drilled piers - typical center section)

S<1mp1e Blows I M[)illtul'& Dl'y Unit O<:ipth DESCFHF'TION Deptl"I plll' I Co11t1;1nt Weight (ft) L.og Cleared ground ~H) foot <%1 (!)Cf) Sur'fl:lce

Brown CLAYEY SILT (ML) firm, damp ! 1

' -2 -3 -4 -• ! 5

I -6 / Gray-green SERPENTINE, firm, damp

- y 7 -

8 -

9 -10 - (grading harder with depth below

I I nine feet) 11 -12 -

13 -No free water encountered. Bottom

14 - varied from 10 to 16 feet in depth.

--

- - - --

--

PLATE ,2

CONSUL TING QUALITY CONTROL ENGINEERS

• Lot 182, Kerrigan Dr. 4250-1. 7-8-78

---------------- ..j¢b,Ni;i, --------- Drilling Oate -------------

Elqvation ------------- Driving Weight ------- Dfop H6il;lht

BORING LOG (Drilled piers - typical south side)

Sample I Blows Moi!ture Ory Unit o~i;:itl'I DESCRIPTION Depth pl;llr Content Weight (ft) Log Cleared ground ('ft\ i foot (%1 (i:)Cf) Surf~c;:n

Brown CLAYEY SILT (ML) firm, damp I 1 I L-

I 2 .._

3 '--

4 -• 5 -

6 -7 _I

- Brown SANDSTONE, hard, damp 8 _/

9 '-

10 '-

11 '--

12 '--

13 -14

I -

15 (grading harder below 15 foot depth

-

16 -..• ·- 17 . ' -·

18 -- - -19 ~ No free water encountered. Bottom varied

between 16 and 20 feet. 20 -

?I1A1rE 3

•

•

•

Consulting Quality Control Englnoors 431 No. Budltln.n Cl!'CI•, 116 •P•(;hteO., C.. Q.\653 • (415) 825-3311

June 11, 1979 File No. 4250-1

•

Neil H. Zickefoose & Associates 3767 Dam Road P.O. Box 967 Richmond, CA 94803

Re: Section Profile Lot 182 Kerrigan Drive

Dear Mr. Zickefoose:

At the request of our client, Mr. Henderson, we are en­closing a section profile made up from the log of drilled piers.

Also enclosed are the general logs as reported on February 5, 1979. As the conditions were quite uniform, specific logs of each pier hole were not made. The general conditions encountered were recorded as indicated. Any specific pier condition should not vary by over one foot as shown on the February report.

Al3:dg cc: 2

We trust this provides the information requested.

Very truly yours,

CONSULTING QUALITY CONTROL ENGINEERS

~.,$~ Alexander Buller Civil Engineer

1 Henderson & Sons Const. Co. 344 Westline Dr. #107 Alameda, CA 94501

~-•~~~~~~~•~~~~~~---·<-­

C [] CE:

562

558

554

55() .µ <II <II ~

54 6 .;:;

~1 0

542i :;:JI

r~ 538L l>i

West Side

.•

Sea le : 1" = 8 '

Residence

~--c~ Original Ground Surface

Gray-Green Serpentine

Bottom of Pier Holes

•

East Side

SECTION THROUGH CENTER OF RESIDENCE

CONSULTING QU).UTY CONTROL ENGINEERS FILE

4250-1 FIGURE 1

•

•

CONSULTING QUALITY CONTRQ~ ;::;'l':iiklii:I:;;:;

CI E@ I 1 • o'•~

431 No. Buch.ei11jln Circle, #16 • Po11checo, Ca. 945!.iJ • {41~) 826-3311

February 20, 1979 File No. 4250-1

Neil H. Zickefoose & Associates 3767 Darn Road P.O. Box 967 Richmond, ca. 94803

Re: Section Profile Lot 182 Kerrigan Drive

Dear Mr. Zickefoose:

At the request of our client, Mr. 'Henderson, we are enclosing a section profile made up from the log of drilled piers .

AB:dg cc: 2

We trust this provides the information requested.

Very truly yours,

CONSUL~NG QUALITY_S9,T~J:_ ENGINEERS

4te_ / . ., ___ ,,{._ .... .... .,......,.,.._.. ,~;~~", J /,f"'il"fl"" tr .. .,,,, v ~

Alexander Buller civil Engineer

l Henderson & Sons Const. Co. 344 Westline Dr. #107 Alameda, Ca. 94501

• cg b~

510

5$0

Sf-0

530

szo

It I SCALE: I~ 20

N

ft

•

RESlDENCE

ORIGINAL GROUND SURFACE PRESENT GROUND SUF\ FACE

BOTTOM L\NE OF DRILLED PIERS

LOT 182 -KERRIGAN DRIVE

s

SOIL AND ROCK CONTACT

Sf!cVoN A c 1'/o~/ //L o,VG £ 115/ rf!c6

CONSUL TING QUALITY CONTROL ENGINEERS FILE .

FIGURE I 4250- I

c-~&-~f-"O~;,~NIA D~Vi.SiON Of -~H\~~S AND GfOlOGV CDMG NOT!:

...,, • ,;;,,or..: HEAi.lOUAHT::r~s

RESOURCES BUILDING ROOM 1341

1416 NINTH STREET SACRAMENTO CA 95314

NUME!ER 49

GUIDtLINES FOR EVALUATING THE HAZARD OF SURFACE FAULT RUPrURE

These guidelines are to assist geologists who.investigate faults relative to the hazard of primary surface rupture. Subse­quent to the passage of the Alquist-Priolo Special Studies Zones Act (1972), it has become apparent that fault investigations conducted in California are frequently i ncon1p I ete or otherwise inadequate for the purpose of evaluating the potential of surface fault rupture. It Is further apparent that statewide standards for investigating faults do not exist.

The investigation of sites for the possible ha2ard of surface fault rupture is a deceptively difficult geologic task. Many active faults are complex, consisting of multiple breaks. Yet, the evidence for identifying active fault traces is gener-

•

lly subtle or obscure and the distinction ctween recently active and long-inactive

faults may be difficult to make. Once a structure is sited astride an active fault, the resulting fault-rupture hazard cannot be mitigated unless the structure is re­located, whereas when a structure is placed on a lands] ide, the hazard from lands] iding often can be mitigated. Further, it is i~practical from an economic, engineering, and architectural point of view to design a structure to withstand serious damage under the stress of surface fault rupture. Thus, the evaluation of. a site for the hazard of surface fault rupture is a difficult and delicate procedure.

Because of the complexity of evaluating surface and near surface faults and because of the infinite variety of site conditions, no single investigative method will be the best, or even useful, at all sites. None­theless, certain investigative methods are more helpful than others in locating faults and evaluating the recency of activity •

• The evaluation of a given site w.ith regard to the pdtential hazard of surface fault rupture is based extensively on the concepts of recency and recurrence of faulting along existing faults. In a general way, the more recent the faulting t''.r ~rr~t~r rhe probgbi]icy for future

faulting (Ziony and others, 1973). Stated another way, faults of known historic activity during the last 200 years, as a class, have a greater proba­bility for future activity than faults classified as Holocene age (last 11 ,000 years) and a much gre.ater probabi I ity of future activity than faults classified as Quaternary age (last 2-3 million years). Moreover, future faulting generally is expected to recur along pre-existing fauits (Bonilla, 1970, p. 68). No doubt there are and will be exceptions to this, because it is not possible to predict the precise surface location of a new fault where none existed before.

As a practical matter, fault investi­gations should be directed at the problem of locating existing faults and then attempting to evaluate the recency of their activity. It is pointed out that data are obtained both from the site and outside the site area. The most direct method of evaluating recency is to observe (e.g. in a trench or road cut) the young­est geologic unit faulted and the oldest unit that is not faulted. Recently active faults also may be identified by direct observation of young, fault-related topo­graphic features in the field, on aerial photographs, or on remotely obtained images. Other indirect and more inter­pretive methods are identified in the out] ine below. Some of these methods are discussed in Taylor and Cluff (1973), Sherard and others (1974), Slemmons (1972), Bonilla (1970), and Wesson and others (1975), but no comprehensive manual on the subject of fault investigation and evaluation exists at this time. Other specific and general guide] ines on fault investigations and evaluations are listed in the Selected References below.

The following annotated outline provides guide] ines for a complete fault investigation that may be applied to any project site, large or small. Fault in­vestigations may be conducted in conjunc­tion with other geotechnlcal inv~stigations

(see CDMG Notes 37 and 44). Althau~h cat

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i I ~ I IJ·j L

~e employed in evaluati1lg a given site, the outline provides a check-list for preparing complete and well-documented re.ports. Since most reports on fault investigations are filed with and reviewed by locwl or St~te government agencies, it i$ necessary that the reports be adequately documented and carefully wrltten to facl]­itate. that review. The importance of the revi~w process is stressed here, because it is the reviewer who must evaluate the wdequacy of reports, interpret or set standards where they ilr"e uncleilr, and. advise the governing agency as to their acceptability.

The scope of the investigation is dependent not only on complexity and

level of risk nc~ei->i:t~u.c 1ui ·Lhc proposed structure 01· development (Joint Cornrnittee on Seismic Safety, 1974, p. 9), Obviously, a more detailed investlgation should be made for hospltals, high-rise buildings; and oth~r critical or sensltive structures than for low-density structures such as wood~frame dwellings that are comparatively safe. The conclusions drawn from any given ~et' of data, however; must be cons is tent and unbiased. Recommendations must be clc~rly separated from conclusions, since recommendations ~re not totally dependent on geologic factors. The final decision as to whether, or how, a given project should be developed lies in the hahds of the owner and the governing body that must review and approve the project.

s·uggested Outline for Geologic Reports on Faults The fol lowing subjects should be addreosed, or at least considered, in any geologic

report on faults. Some of the investigative niethods listed below should be carried out well beyond the site being investigated. However, it is not expected that al I of the methods identified would be used in a single Investigation.

I. Text

A. Purpose and scope of investigatlon

B. Geologic setting

C. Site description ~nd conditions. Include information on geologic units; graded and filled .;lreas, vegetation, exist1ng structures; etc.; that may ~ffect the choice of investigative methods and the interpretation of data.

D •. Methods of investigation

l. Review of published and unpublished literature and records concerning geologic unit~, f.;lults, ground-water barr 1i8'rs.. etc.

2. Interpretation of aerial photographs and other remotely sensed images to detect f~ult-related topography, vegetation and sotl contrasts, and other lineaments of possible fault origin.

3. Surface observations, including mapping of geologi~ units and structures, topographic features, springs; deformation of man-made structures, etc., both on and beyond the site.

4. Subsurface investigations

a. Trenching and other extensive excavations to permit detailed and direct observation of continuously exposed geologic units and features which must be carefully logged (see Taylor and Cluff, 1973).

b. Borings and test pits to perrnit collection of data on geologic units and ground water at specific locations. Data points must be sufficient in number and adequately spaced to permit val id correlations and inter­pretations .

5. Geophysical investigations. These are indirect methods that require i3i

knowledge of specific geologic conditions for reliable interpretations.. They should seldom, if ever, be employed alone without knowledge of the geology. Geophysical methods alone~ prove the absence of a fault nor do they identify the recency of activity. ·The types of equipment and techniques used should be described.

•

•

•

a. Seismic refraction

b. Magnetic Intensity

c. Other (e.g. electrical resistivity)

6. Other methods should be included when special conditions permit, or requirements for crltlcal structures demand, a more intensive investigation.

a. Aerial reconnaissance overflights.

b. Geodetic and strain measurements, microseismicity monitoring, or other monitoring techniques.

c. Radiometric analysis (e.g. Cl4, K-Ar), stratigraphic correlation (fossils, mineralogy), sotl profile development, paleomag~etism (magnetostratigraphy), or other age-dating techniques to identify the age of faulted or unfaulted units or surfaces.

E. Conclusions

I. Location and existence (or absence) of hazardous faults on or adjacent to the site.

2. Type of faults and nature of anticipated offset: direction of relative displacement, and m~ximum displacement that is possible.

], Probability of or rel~tive potential for future ourface ~isplacement. The I ikelihood of future ground rupture can seldom be stated mathematically, but may be stated in semiquantttative terms such as low, moderate, or high.

4. Degree of confidence in and limitations of data and conclusions .

F. Recommendations

l. Set-back distances frOm hazardous faults, if appropriate. State and local law may dictate minimum standards (e.g. see Hart, 1975).

2. Need for additional studies.

3. Risk evaluations relative to the proposed development--oplnions are acceptable. But remember that the ultimate decision as to whether the risk is acceptable lies with the governing body.

I I. References

111.

A. Literature and records cited and reviewed.

B. Aerial photographs or images interpreted--] is.t type, scale, source, index numbers, etc.

C. Other sources of inform~tian including well records, personal communications, and other data sources.

lllustrations--these are essential to the understanding of the report and to reduce the length of text.

A. Location map--identify site locality, significant faults, geographic features, seismi~ epicenters, and other pertinent data; 1:24,000 scale is recommended .

B. Site development map--show site boundaries, existing and proposed structures) graded areas) streets, exploratory trenches, borings, geophysical traverses, and other data; recommended scale is l Inch equals 200 feet, or larger.

3

•

•

•

C. Geologic map~~shows distribution of 9cologii; unit~ (if mof"e than one), faults and other structures, geomorphic features, aerlal photo lineaments, and springs; on topographic map l :24,000 scale or larger; can be combined with Ill (A) or Ill {B) •

D. Geologic cross-sectionsf if needed to provide 3-dlmensional plcture.

E. Logs of exploratory trenche>, and borings--show details of observed features and conditions; should not be generalized or diagrammatic.

F. Geophysical data and geologic interpretations.

IV. Appendix--supportlng data not included above (e.g. water well data).

V. Signature ~nd registration number of investig~ting geologist.

Selactcd Reforoncou

Association of Engineering Geologists, 1973, Geology and earthquake hazards -- Planners guide to the eeismic safety element: AEG, Southern California Section, 44 p. (See Section II on Evaluating the Problem.)

Bonilla, M.G., 1970, Surface faulting and related effects in Wiegel, R.L. (Edit.), Earthquake Engineering, Prentice-Hall, Inc., Englewood ITiffs, N.J., p. 47-74. (Contoins an extensive bibliography on surface faulting, fault· patterns and types, width of f~ult zones, creep, etc.)

California Division of Mines and Geology, 1973, Guide! ines to geologic and seismic reports; CDMG Notes 37.

California Division of Mines and Geology, 1975, Recommended guidelines for preparing engineering geologic reports, CDMG Note 44 .

Hare, E.W., 1975, Fault hazard zones in California: California Oivlolon of Mines and Geology, Special Pub] ication 42, 37 p. (revised yearly; information on state low and zoning program for regulating development near hazardous faults).

Joint Committee on Seismic Safety, California Legislature, 1974, Meeting the earthquake challenge: California Division of Mines and Geology, Special Publication 45, 223 p.

Sherard, J.L., Cluff, L.S., and Allen, C.R., 1974, Potentially active faults in darn foundations: Geotechnique, v. 24, no. 3, p, 367-428, Institute of Civil Engineers, London.

Slemmons, D.8., 1972, Microzonation for surface faulting in Proceedings of the Inter­national Conference on Microzonation, Seattle, Washington, October 30 ~ November 3, 1972, p. 348-361.

Taylor, C.L., and Cluff, L.S., 1973, Fault activity and its significance assessed by· exploratory excavation in Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System: Stanford University Publication, Geological Sciences, v. XIII, September .1973, p. 239-247,

Wal lace, R.E., 1975, Fault scarp geomorphology and seismic history, north-central Nevada (abstract): Geological Society of America, Cordllleran Section, ]lst Annual Meeting -- Abstract with Programs, v. 7, no. 3, p. 385,

Wesson, R.L., Helley, E.J., Lajoie, K.R., and Wentworth, C.M., 1975, Faults and earthquakes in Studies for Seismic Zonation of the San Francisco Bay region: Geological Survey Professional Paper 941-A, p. A5-A30 •

future U.S.

Ziony, J.I., Wentworth, C.M., and Buchanan, J.M., 1973, Recency of faulting; A widely applicable criterion for assessing the activity of faults: World conference on Earthquake Engineering, Fifth (June 1973), Rome, Italy, p. 1680-1683.

EWH 10/?5

•

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•

the delta region between the hills in the Stale Po1rk and the levee of th~ no1·1hern· most distributary (figure 8). As a result of the damming etTect, water wa5 ponded in the upper portions of the old tidal chan­nel drainage system, salinity has in­crc:a.sed, the Salicornia has died, and a significant amount of the salt marsh's or­ganic productivity has been lost.

Several very large salt pans exist along Los Osos Crcekj between the SoutlJ Bay Boulevard bridge tind the site of the old bridge (seen in figure 3) which w•·•S washi;d out in 1969. The salt pans lie bctwi...-e11 the levee and thC hill beside .T url'i Road. This. area of the salt marsh can be seen frorn the hillside. The salt pans have e)l.panded since the new bridge was built, because the bridge ha.s dammed off the bnck-levee drainage.

INTERTIDAL MUDFLATS

The pickleweed salt n1arsh rerresents an almost flat plane th~1l 1narks. the top sud'"a.ce of the delta. llowever, the delta is a three din1ensional landforn1, and has a. frontal region that is advancing into the bay. The frontal region is i11l intertidal mu<lllnt that is submerged for periods too extensive for the survival of Sa.Jicornia, <-l.rid it is barren of most other marine plan.ts (figure 3). Sirnilar mudflats in San Francisco Bay are described a11 high tidal flats (l'estrong, 1972).

Rl:G ISTRA TIO N BOARD'S POLICY

GUIDELINES The Sti'1te Hoard of Rcgi!;tr11tior\ for

(.leologists and G1..'0physicl~t!T. nH~t with rcgulaiory geologists fron1 cities and counlies throughout California, wjth Di­vision of Mines and Geology personnel, with representatives of ussociations, and with individual co11sultants to discuss possible vioh1tion ... of the Act and prac­tices which n1ay not be violations of 1hc A<.:l h1Jt sub~tantially alTccl the ('lublic. Three meetings were held .1111d over 20 p.artlcip.arH~ di!i.Cuss~d Ilic 11dequncy of .'l:\~Oiov,ic rep01'1!>11 Juhl the rcsponsihilitj' of llic ho11l'tl 1 the rl~Vit:w agcucic~. and the cu11;,11h11n1s 10 lhe puhlii:.

As a rl·sull of tht:se n1ecli11g:>i1 the bottrd !11·\·id~·al 11101 1'Csp1111:i1ihlc Jott•ol1i~ic w11rk is n·pl'~~1;1•111cd hy Ilic ~uh.Jclin~s for praclicc

The high tidal flat within the Chorro dcltn is well developed at the nloulh of Los Osos Cr~k (figures 3, 4). Jlete the region is extensively gullied by fan-like grou1,ings. of small rills or channels that cut across the: lc:vees of the main distribu­taries. The rills appear to· be caused by erosion of sediment recently deposited on the levees during floods. Apparc:ntly very large amounts of sediment an: deposited in the area at high tide during floods, The sedi1ncnt is ei·oded by t.hc s:1.1n~ floods during low tid~. Gullit--s ~ri:: therefore cut during floods, but rcrnni" open aft.er t.he flooding: because of the enhanced ~idal flow within the gullies con1parcd to the shallower intcrgully areas. The rills are a~sociated with bends in the distributary channel as it crosses the tidal fn.lt, and arc genetically related to the fact that fast flowing wnter will bank us it passes around a channel bend, thus flooding out of the channel at th-ilt point.

At the base of the advancing sedin1ent pile of the delta, reprc5e11ted by the high tidal Out, is the lower tidal flat which is exposed only at- low tide. The area is a mudflat, contains less silt and more clay than the higher tidal flat., and has very little slope. The lower tidal flats of the Chorro dc:ltn. are actu~lly seditnent ponds trapped between the delta front and the tidal levees that border the main tidal ch~1.n11els of Morro Bay. Two channc:ls from the delta area have been kept open into the main Morro Bay channel through

issued by the California Divi~ion or Mines and Geology for lhc invi:stiga.tion of geo­logic hazards ~'nd the preparation of re­ports a.s C:1lifor11ia Division of Mines and Gc.~ology Notes Numbers. 37, Guidelines to Ueologic/Seismic Reports; 4], Rtco1n­incndcd Guideline!!. for Deter1nining the Maximu11'I Credible and the Maxin1un1 Probable Earthquakes; 44, Rci;Ommend­ed Guidelines for Pttpariilg Engineering Geologic Repo1·ts; 46. Guidelines for Geologic/Seis1nlc Considerations in En~ viro111nental l1npact Reports; 47. R(.'1;0tn-1nended Guidelines for Geologic Rcpt)tts. on O!Tshore Operations and facilitie:s: 48, Checklists for the Review of Gi:ologic/ Seisn1ic Reports; and 49, Guidelines for Evaluating the Ila:.e.a.rd of Surface Fault Rupture.

1'h\! b~\ard has adopted these guidelines i1s its roli\.·y stat ... ~111cnt on thi.: 01dcquacy t)f profc:-;~ion.al g..:ological work \11u.lc1 Scc-1io11 7~60(c) of lhc Business ond Prt)ft.:s­s~1)us (,~ndc fnr lhc gcologk· pn)fc-ssioo io Culit;)rni11, Th..: guic.Jc-liocs will be u~d to

March 1979

the ti~lal levee. One channel is supplied by the northern nlost distributary of Chorro Creek, and the other by Los Osos Creek and other distributaries of Chorro Creek. The channels in this area -.re permanently .submerged.

SUMMARY

Chorro delta displays all of the geomor­pholo,gic features associah .. -d with large deltas. ·One cn.n see distributaries, tidal i::h~~nnel$, levees1 and the classic topsct, roreset~ and bottomset areas within a few square miles. The outer regions of tl1e del­ta can best be viewed fron1 the north end of 9th Street in the community of Hay­wood Park.

REFERENCES

Ocrdc:s, G.L., Primbs, E.R.J .. and Browning, B.M., 1974, Nall.Ital resour~ of Morro Day; their stat.u!lo and future, Coastal Wet­lands Series No. 8: California Dcp.arhnent Of Fish and Game.

Gilbert, G.K., P~85, "I'hc topographic features. of lake shores: U.S. Geological Survey, 5th An11ual Report, p. 87.

Morgan, J.P., l970, Dcposition11l proc-~~C!l. and products in the deltaic cnvironmi::nt iJJ Del­taic sedimentation, 111oder1l and. :ancient: S(l(;:icty of EtoI101nic Paloontologists and Miileralog(st.s, Special Publication 1-'~ edi­tor, J.P. Morgan, p, 31--47.

Pestrong, R., 1972, San Francisco Bay Tide· lands: Califoroia Geology, v, 25, no. 2, p. 27-40_ ~;;

facilitate a screening of the geologic re­ports for violations of SectiOII 7860(c).

The boo.rd suggests that all regulatory agencies considc:r·a.cto1~tion of these not(..i§. or i::quivalency as guidelines for inve~lig;:i.­tion and for rcporl prc:pun1tio11. Also, ir urges all geologists to utilize the proce­dures t)Ulli11ed i11 the notes when they iil­vestigate conditions at a project a11d when preparing rcPQrts.

Agel1cies can establish more stringeI1t guidelines for reports and arc not restrict­ed by the policy statement from develop· ing additional requirements for specific geologic conditions.

The policy became elTective January l, 1979. Rtports dated subsequent to th~t · dute will be reviewed for their adequacy when they are submitted 10 1he bourd. Re­ports submitted to governmental agencies befure January 1 will not be revic:wed for adequacy unless a complaint is filed with the board. ~

57