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341, Construct a 787 sq. ft. guest , Studies & ReportsLockwood -Singh & Associates . A COflrORA rioN Consulting Foundation Engineers and Geologists 1944 Cotner Avenue: • Ins Angeles. California 90025 Telephone. (213)870-7335: (213)477-8208 ,•u,e , , , w:a•. . .. Project Ref. 3215-53 March 22, 1935 Mr. Allen Steele, Jergins Trust Building, Suite 910 120 E. Ocean Boulevard Long Beach-, California 90802 SUBJECT: REPORT OF PROFESSIONAL GEOLOGIC OPINION RESIDENCE PROPERTY NO. 7 CREST ROAD EAST ROLLING HILLS, CALIFORNIA Dear Mr. Steele: In accordance with your instructions the undersigned has examined the above referenced property to assess the general geologic characteristics. Eight test pits were excavated with a track mounted backhoe in the area to the southwest of the existing residence for the purpose of exposing bedrock strata beneath the soil profile since the only other exposures of bedrock on the property are in the low cut slope adjacent to Crest Road. A geologic sketch map is included herewith, Plate A, to delineate the location of the pits, attitude of bedrock strata, and the 'thickness of the soil cover. Pcf . 3-15-'53 March ZZ, 1985 1OC i T• I ON AND TOPOGRAPHY 'ihe subject property occupies a location near the crest of the central portion of the Palos Verdes peninsula. The existing residonce is located on a near level pad area that was created by grading off the top of a low rids: : e ,c a,s southwast from Crest Road. The place as a fringe fill around the perimeter of. tLe building pad. To the southwest the property descends about 90 feet to the adjacent ownership. A steep walled southwest trending drainage course is located b::''sveen the subject property and the adjacent property tc,: the southeast. Drainag. by sheet flow runoff down the westerly slope with a portion directed to the drainage course on the southeast. No conditions of adverse erosion due to runoff was noted at the time of the examination. Any future remodeling or reconstruction on t h r, ;itc pr>> dr• adequate facilities to control 17 , ,, , to minimize the likelihood of Project Ref. 3215-53 March 22, 1985 GEOLOGIC CONDITIONS Fill The fill encountered at the base of the fringe fill comprises a mixture of soil and bedrock fragments.' AIthough reasonable firm in character, it was probably not placed under an engineers control and thus lacks adequate compaction to meet current Code standards. Cement walkways located in the fill exhibit evidence of fill settlement and creep toward the fill slope. Similarly the top of slope at the rear of the house appears to have settled to a degree that the yard drainage is toward the slope. Any future grading or landscaping should correct this condition and control the drainage to prevent runoff over the slopes. Soil Soils overlying the bedrock strata range in thickness from a 1 foot near the pad area to a maximum of about 11 feet on the lower slope (refer to Plate A). The clayey character of the brown soil reflects the high content of bentonitic clays that prevail in the underlying bedrocks from which the soil developed. Project Ref. 3215-53 March 22, 1985 Bedrocks Bedrocks underlying the site comprise of siliceous and bentonitic siltstone and shale strata of the Altatnira member of the Monterey Formation of Miocene geologic age. At the locations exposed in the test pits these strata were noted to range from buff to orange buff in color and to exhibit well-defined bedding plane structures. The i firmer beds part readily along bedding planes. Fractures are universally present near surface that create small sub -angular shards that are characteristically found in the overlying soils and fill materials. Project Ref. 3215-53 March 22, 1985 GEOLOGIC STRUCTURE The formation of the Palos Verdes'Iiills resulted, in part, from the upward arching of the once horizontal sequence Altamira strata. The anticlinal structure thus formed has its axis approximately coincident with the topographic crest of the hills. In general, the beds to the south of the crest dip southerly, and the beds north of the crest dip to the north. Superimposed on these general regional trends are numerous minor flexures. Since the subject property is situated close to the crest of the hills, the anticipated attitude of the underlying strata is one of low dips. This condition was confirmed by the observations in the test pits. Dip angles ranged from horizontal near the lower property boundary to a maximum of 14° adjacent to the house. The directions of observed dips were predominantly to the south or slightly west of south with a dip of 4° to the northwest (Test pit 8). Dip attitudes are neutral from the standpoint of gross geologic stability of the west facing descending slope. Project Ref. 3215-53 March 22, 1985 LANDSLIDES The subject site is located north of the Flying Triangle landslide area. This ancient Landslide has be(!n r. (:i•rit ly reactivated and caused damage to several structures within the active area. Recent movements have occurred in two separate areas, one to the southwest of the subject property and the other almost due south. The southwesterly line of the subject site is an estimated 800-1000 feet northerly of the closest slide affected area on the southwest and 600-700 feet from the movement area to the south. The area of slide movements on the south is separated from the subject property by the previously mentioned drainage in the proximity to the southeasterly property line and an intervening ridge swath el" the drainage. Project Ref. 3215-53 March 22, 1985 CONCLUSIONS Geologic conditions observed at the site appear favorable for continued site stability. The property was not involved in the movements of the ancient Flying Triangle landslide nor in the recent ones. The low dip orientations observed would indicate that the likelihood of future involvement in any Flying Triangle slide movement or instability is remote. Future site development in the vicinity of the present constructions appears feasible from a geologic standpoint, subject of course to all the normal requirements required by applicable codesand good engineering practice. A detailed geotechnical report discussing a specific plan of development will undoubtedly be required by the controlling agencies prior to issuance of permits for construction. Thank you for this opportunity to be of professional service. If you should have any questions concerning this report, please contact the undersigned. Respectfully submitted, LOCKWOOD-SINGH $=,ASSOCIATES Bruce Lockwood CEG 204 7 ,3 TP1 0 LEGEND • Strike & Dip of Bedding Approx. Location of • Exploratory Test Pits ED Horizontal Bedding n Soil Thickness (in feet) 1 TEST PIT LOCATION MAP Proj. No. Date. STEELE-4.7 Crest • 3215-53 March, 1985 PLATE A 1 /'1 r•V1Ar rI fl rl_ c'rs onri 0 A r. r'r 1't It T r r'