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474A, Construct a detached 3-car gar, Studies & Reports• MAIN 0/PICC 111S WILSHIRE BLVD.. LOS ANGELEI 10017 • 21) • 111.1110 Mr. A. E. Esser 23 Crest Road East Rolling Hills, California 1202 LAST 17TN /TRttT. SANTA ANA 111701 • 711 • 111.11t1 2.7• CAST MAIN ITRtCT. VENTURA 11001 • SO) • •41.11L1 MAURSETH • HOWE • LOCKWOOD & ASSOCIATES Consulting Foundation Engineers and Ceologisu Los Angeles, California February 3, 1967 Project No: 3891-G Engineering Geologic Investigation 23 Crest Road East Rolling Hills, County of Los Angeles Dear Mr. Esser: Pursuant to your request this facility conducted an engineering geologic investigation on the referenced property to evaluate factors perti- nent to the development of a stable site. Investigation included surface geologic mapping and examination of seven hand -dug test pits. Field work required approximately one day. Geologic data are delineated on the accompanying geologic section and 40-scale topographic map and grading plan, dated November 1, 1966, furnished by South Bay Engineering Company. SITE . CONDITIONS Location and Topography The property under discussion is situated on the south flank of the Palos Verdes Hills, at a sea level elevation of 1250 feet, approximately one - quarter mile west of San Pedro Hill. The proposed site comprises approxi- mately two and one-half acre parcel adjacent to an existing residence. Access RAY O. MAURSETH. C.C. CHARLEI 1. HOWE JR.. C.C. JOHN I. HOWE. C.E. R. IRUCC LOCKWOOD. GEOL.•P.C. ALICRT IACA ROBERT D. COUSINEAU RICHARD P COUSINCAU. GEOL Project No: 3891-G 2 to the residence is by way of a private drive from Crest Road. The site embraces the upper portion of a south -trending ridge, bi- furcated south of property. The elevation of the proposed building area.is 1220 feet above sea level. Slopes of the property within the area to be de,- veloped is about 3:1. Surface relationships of the site reflect the existance of an ancient marine terrace platform that has subsequently been greatly modified by erosion. The two relatively deep south -trending canyons parallel the east and west boundaries of the subject property. The lower canyon slopes are approximately 1-1/2:1, decreasing to about 2-1/2:1 within the site. Vegetation comprises sparse chaparral, small planted trees, and a dense growth of annual weeds and grasses. Peripheral slopes comprising the upper areas of adjacent canyons have an exceedingly dense chaparral growth. Drainage Site drainage comprises essentially sheet flow runoff of incident rain- fall derived within the property and from the fill slope of the adjacent resi- dence above. Drainage from the existing residence area is carried off by paved surface drains to discharge points east and west of the pad. Runoff is conducted to locations below the toe of the fill, retarded by rip -rap velocity breaker, and then dispersed to the canyon below. No adverse effects of erosion were noted. Soil moistures at the surface and in test pit excavations appeared normal. No free ground water was noted or is anticipated within depths that would affect the proposed grading. Project No: 3891-G 3 Proposed Development Cut -and -fill grading to develop a residence site and adjacent stable area is proposed. Both cut and fill slopes are planned at 1-1/2:1. New slopes will have maximum heights of approximately 30 feet. The graded area will be connected by a long (600 feet) drive connecting to an existing private drive. A private sewage disposal will be required. GEOLOGIC CONDITIONS Surficial Materials Fill No fill was observed on the site proposed for grading, although scatter- ed rock and boulder spoil is common on the upper slopes. These rocks, com- prising primarily blocky silicious siltstone, doubtlessly originated during development of the adjacent pad area. Soil Soil on the site is comprised principally of slope wash debris derived from up -slope areas. Test pit excavations revealed the material to range from one to three feet in thicknes$. Slope -wash is a loose mixture of shale chips, fragments, and blocks in a dark brown clayey sandy silt matrix. The similarity of the clayey fraction of this material with other soils in the area suggests a moderate degree of expansiveness may be anticipated. Expan- siveness is .that physical property in which a volume change accompanies a change in moisture content. Slope -wash debris is so widely distributed over the site that deline- ation on the accompanying map was deemed unnecessary. Geologic • • Project No: 3891-G 4 relationships are shown on the map as if no soil materials were present. Terrace Material As delineated on the geological map and cross-section, the proposed site is in part underlain by nonmarine terrace deposits, which are similar to slope -wash, but in general are firm and often lightly bonded with calcareous cement. Nonmarine terrace materials are generally cream to buff in color and poorly stratified to massive. Based on topographic considerations, the nonrnarine terrace remnant at the site is estimated to be 35 to 40 feet.thick. Marine terrace deposits, which commonly form a thin fossiliferous veneer on the underlying wave -cut bench, were not exposed by subsurface investigations, and thus, may or may not be present. BEDROCK Altamira Shale Rocks underlying the subject property are indurated marine siltstones and shales of the Altamira member of the Miocene Monterey formation. These strata are typically buff to medium brown, thinly bedded, siliceous and argillaceous siltstones. Occasional interbeds of calcargillite and highly bentonitic siltstone•are also present. GEOLOGIC STRUCTURE The area ofthe proposed grading is located in the area of noprnarine terrace materials, which are essentially massive and homogeneous insofar as gross engineering properties are concerned. Strata of the Altamira Shale have a northerly dip, numerous minor deviations of attitudes due to minor folds are common. The interpretation • • Project No: 3891-G 5 of the geologic structure is presented on the accompanying geologic section. GEOLOGIC STABILITY No evidence of recent or past instability was observed on the subject property. The northward inclinations of bedding beneath the nonmarine terrace cover are favorable for continued geologic stability of the area following grading. CONCLUSIONS AND RECOMMENDATIONS 1.0 General It is the professional opinion of the writer that the subject site is geo- logically feasible for the proposed development, subject to the following specific recommendations: 2.0 Cut Slopes Cut slopes in nonmarine terrace materials are anticipated to be geo- logically stable at slope inclinations not exceeding 1 1/2 horizontal to 1 vertical. Proposed cuts in Altamira Shale bedrocklikewise shall not exceed a slope inclination of 1 1/2 horizontal to 1 .vertical. No cuts shall be made in which there is a significant component of dip out of the slope in the absence of further investigation as the degree of anticipated stability by the engineering geologist and soils engineer. It is suggested that soil cuts be no steeper than 2 horizontal to 1 vertical. 3.0 Foundation Support Firm nonmarine terrace materials and subjacent bedrock are concluded to be geologically suitable for support of the proposed engineered fill. It is recommended that terrace materials used for support of fill be evaluated by the soils engineer in order to verify its suitability. Project No: 3891-G 6 4.0 Fill A11 fills shall be placed in accordance with the Los Angeles County Grading Ordinance, and subject to the approval of the soils engineer. Physical examination of site materials suggests them to be suitable for use in proposed fills. 5.0 Drainag Drainage shall be dispersed in a manner to preclude concentrated runoff over graded and natural slopes in accordance with the.requirements of the Los Angeles County Code. 6, 0 Se\/IY ago Disposal Favorable geologicfactors mitigate the necessity of special seepage pit design requirements. Location of the seepage pit shall be such that the possibility of future saturation of fill shall be minimal. The seepage pit location and depth of the permeable section shall be reviewed and approved by the engineering geologist prior to construction. 7.0 Inspection During Grading It is recommended that the engineering geologist inspect the site during grading to verify the findings of this report, and be in a position to make further recommendations, if required, to provide for future safe development of the site. Should you have further questions concerning this report, please feel free to contact the writer. RBL/WRM/sl Very truly yours, MAURSETH, HOWE, LOCKWOOD & ASSOCIATES eZu c( R. tgruce Lockwood Engineering Geologist