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HomeMy WebLinkAboutm1030TESTING • INSPECTION 1781 CALLENS ROAD VENTURA, CALIFORNIA 93003 PHONE (805) 642.6727 - (805) 497-2401 77-6=162 June 21, 1977 Job No. B-7699-VOI PROJECT: Equestrian Center Site Diamond Bar'J' Puente Hills, Los Angeles County, California. SUBJECT: County of Los Angeles Evaluation of Addendum 41, Conditional Use Permit No. 1030 dated February 8, 1977; and Addendum #2, Conditional Use Permit No. 1030 dated May 4, 1977. In February 8's evaluation, there are thirteen (13) items listed and five (5) items in May 14's evaluation. In answering the February 8 evaluation, all five (5) items of May 14 will be answered. The February 8 evaluation will be treated by this addendum in the order listed. Item la -requests the following data: "Geotechnical Con- sultant report of August 7, 1964, including boring logs." The writer was not able to get the report from Geotechnical Consul- tants; however, they did send us the eight (8) boring logs with their mapperi locations. These are submitted and are attached in the appendix. Item 1.b requests the boring logs of September 18, 1969 report of Stone and Associates to ascertain slide depth and geologic con- ditions. These borings are shown on two (2) cross -sections sup- plied in Stone's Stability of 20 Acre Slide, Diamond Bar. Blvd., dated Septe.niher 13, 1969. The borings are shown as straight boring logs with no details. Stone and Associates were contacted by this office a request for the logs was made. On 6/20/77, communica- tion from Stone and Associates indicates boring logs would not be released. ENGINEERNG GE-0-LG , SECTION `UL071y,7j SANTA BARBARA SAN LUIS UBISPO BC5) 495-34 84 i lEL6 OFFICES: THOUSAND Q( 805) 966-9912 (BO5) 544-6157 77-6-162 June 21, 1977 -2- Job No. B-7699-VOI Item 2: "All reports reviewed by the present soils-geoldgic consultant, Buena Engineering, must be referenced. Other pertin- ent reports which may not have been reviewed, include: September 9, 1971 Leighton and Associates --Tract 30289; Medall and Associates, Tracts 33197 and 32974, (Parent Tract 29053); 3 reports of Dr. Mer- riam." All of the above referenced reports were obtained or were reviewed at County offices in Los Angeles. All three (3) reports by Merriam were obtained and are on file in this office. A copy of Leighton and Associates Tract 30289 is also present in this office. Stone" in Item lb above was alsoThepreviouslyreferredto obtained and a copy is in this office. Two (2) reports by LeRoy Crandall and Associates were obtained and copies are in this office. The first is a report of Evaluation of Slope Stability for Proposed Equestrian Estates, Diamond Bar, dated December 26, 1963. The other is a Report of Soil Investiga- tion, Proposed Equestrian Center, Diamond Bar, dated June 2, 1964. In addition to this, following reports by James E. Slosson and Associates were obtained and copies are on file in this office: 1) Geologic Report, Equestrian Center, Diamond Bar, California, March 24, 1971; 2) Equestrian Estates Recreation Area, Diamond Bar, March 3, 1971; 3) Supplemental Review of Grading Plan for Portion of Equestrian Center, dated July 27, 1967; 4) Monthly Progress Report for Equestrian Center, Diamond Bar, California, January l to January, 30, 1966; 5) Second Addendum to Geologic Report on Equestrian Estates, Diamond Bar, California, dated April 18, 1964; 6) Addendum to Preliminary Geology Report on the Equestrian Estates, Diamond Bar, California, September 27, 1963; 7) Preliminary Geologic Report on Equestrian Estates, Diamond Bar, California, July 1963. In addition to the above reports, additional reports by labora- tories and individuals were reviewed at County offices. In this review, reports by John C. Merrill, dated 1971, Lockwood --Singh and Associates, May 3, 1974 and H. V. Lawmaster & Co., August 30, 1972 were also reviewed while at the County. BUENA ENGINEERS, INC. 77-6-162 June 21, 1977 -3- Job No. B-7699-VOl Item 3: "The soils --geologic consultant must approve prior work of others or present alternate conclusions with supporting data. discrepancies between interpretations of prior consultants must be resolved with respect to analysis of the landslide rela- tive to the proposed development. All data, including boring by others, must be shown on maps and illustrations. Existing and proposed grades must be shown and effects on slide stability analy- zed." As stated in our prior report, it is this laboratory's opinion that all prior associations and/or individuals working on this project and adjacent areas are competent soils and/or geolo- gists and in certain cases, discrepancies appear to be due to dif- ferences of interpretation which in no way distracts from the competency of work presented. Perhaps the greatest discrepancy is the delineation of slide perimeters. After reviewing work by others, data submitted by them and data collected by this labora- tory, slide boundaries were established as are indicated on the accompanying map. This delineation of slide boundaries is the result of compar- ing our field work with the results of field tests and studies per- formed by others. This indicated delineation favorably represents out consideration of attendant lines of weakness formed as a result of the slide which would then be reflected by erosional conditions. All data derived by this laboratory from other laboratories and consultants have been included on the attached map. In addition, a second map shows proposed final grades after completion of develop- ment. Item 4: "Existing graded conditions which have not been approved by prior consultant (Slosson; Leroy Crandall) for the equestrian center must be approved. Reports must be reviewed by the new soils --geologic consultant. Slosson and LeRoy Crandall reports were obtained and were reviewed by this laboratory. Per- sonal communcation with Dr. Slosson.and LeRoy Crandall revealed that upon completion of their preliminary soils and geology reports, no further work was performed by their respective organizations per- tinent to the work they reported. Mr. James L. Sanchez of the Dia- mond Bar Development Corp. was contacted and verbally assessed of the situation. Mr. Sanchez reported that grading control work was performed by Donald R. Warren Co. and reports were previously sent to the County. At the writer's request, Mr. Sanchez agreed to re- submit copies of Donald R. Warren's report to the County. On June 7, 1977, a transmittal form was received by this laboratory indi- cating a copy of the final grading report by Donald R. Warren Co., dated 3/7/67, was mailed to the County of Los Angeles. A review of the proposed grading plan will indicate that most of this equestrian site as it is now will be graded out. BUENA ENGINEERS, INC. 77-6-162 June 21, 1977 -4- Job No. B--7699-VOI Item 5:' "Stability analysis for the landslide must assume \ the worst conditions relative to future potential high ground water, unless an adequate drainage system, including at and below Diamond Bar Boulevard is presented." Attached please find sta- bility analysis using worst possible conditions for slide units and using regular test results for buttress and/or shear key. Since the south portion of this area will experience cut, the design fac- tor used was for a buttress. Where that portion is not cut, then the buttress will continue to stabilize the upper slide as a shear key. All testing was performed utilizing 100% saturation of samples during tests. Additionally, since this is a shear key and buttress combination, a French drain system will be required at the slide plane on the upslope side of the buttress or shear key. Buttress - shear key design factor is based on containing the slide that now exists above the proposed facility. Within the proposed improvement area, an exceedingly deep cut area will result and this will elimin- ate surcharge on that area involved in the existing slide's lower portion. Reference is hereby made to the CDMG California.Geology May 1977 to the following article: "Radiocarbon Dating of Landslides in Southern California" by Martin L. Stout, Department of Geology, California State University Los Angeles, pages 99-105. Following quotes are from this article (copy is attached): Page 99, first paragraph, second sentence: "The results.show that most of these landslides occurred between 16,000 and 20,000 years ago during a period of known heavy precipitation which was partly contemporaneous with widespread late Wisconsin glacial ac- tivity (referred to as Tioga stage in California) and greatly lowered sea level." Second paragraph, same page: "Climatic and geomorphic factors usually have a greater effect on subsequent sta- bility. Older landslides may'have had extensive alluvium deposited against the bottom or t-t' thus increasing the stability, or may have been subject to further erosion and undermining, in essence, decreasing the stability. Generally, the degree of consolidation is better in older landslides." Page 102, third paragraph: "Diamond Bar Landslide - The oldest landslide, dated at 19,075 ±510 carbon-14 years BP is.just off Golden Springs Drive near Sycamore Canyon Park in Diamond Bar, east- ern Los Angeles County." Page 104: "Where glacial chronologies are well established with radiocarbon dates, a glacial maximum (furthest advance of gla- ciers) is usually noted between 15,000-20,000 years ago (article gives references). As noted above, the radiocarbon dates of most ancient landslides in southern California coincide with that age range. This most recent glacial advance in California is known as the Tioga stage. It also represents a time of greatly lowered sea level BUENA ENGINEERS, INC. 77-6-162 June 21, 1977 -5- Job No. B-7699-VOl and generally wetter climate. Most scientists agree that sea=level was at least 400 feet Lower during the Tioga than it is at present more references). Some data suggest that it was at least 575 feet lower than present." CDMG report seemingly verifies conditions found by exploration and statements made in this and prior reports, that the landslide is currently stable. Also, it is being buttressed by alluvial materials in its lower portion and in its present condition it ap- pears to be stable. Proposed grading should further stabilize this slide by remov- ing a portion of surcharge from the lower slide portion that will not be stabilized by buttressing and/or shear key. Item 6: "Landslide stability analysis must include effects of proposed grading." This has been answered in No. 5 above. Item 7: "Thickness of alluvium offsite, if influential to stability analysis of slide and grading, must be determined." It is our opinion that due to the fact that a large portion of surcharge is being removed, California Division of Mines & Geology article in- fers that alluvium is helping to stabilize the slide and that the slide has been stable for a considerable period of time, the lower portion below the buttress -shear key will remain in a stable condi- tion. Item 8: "Approval of grading plans and associated reports of Medall and Associates for the proposed development to the south, peripheral to the slide, must be reviewed relative to this proposed development and landslide stability. (See Tract No. 29053)." While reviewing reports at Los Angeles County, the writer reviewed the above report, Tract 29053's proposed development and landslide stability factors. It is our opinion that this is off the site, out of the area and above our proposed shear key so that properly sta- bilized, Tract No. 29053 development would have no effect whatsoever on the proposed buttress and shear key within this area. In fact, it would increase the safety factor, if"anything. Item 9: "Show areas of drainage trenches, etc., recommended by the consultant (Buena Engineering) on plan and sections; consider future development irrigation." Drainage is shown on attached development plans. It is our belief that indigenous type plants would be used for development; however, irrigation is always a prob- lem in that either not enough irrigation is used to keep plants alive or it is over -watered (in this case, this could be a disaster). One alternative would be to use constructed and sealed planters above and underground. Item 10: report: a. Is 'non' water type 'snow' proposed; The following questions should be discussed in the BUENA ENGINEERS, INC. 77-6-162 June 21, 1977 -6- Job No. B-7699-V01 M Are seismic considerations in stability analysis recommended by the consultant?" Aero-Recreation Properties, Inc. informed this laboratory that a non -water type snow will be used. Seismic shown on the Item.11: must be shown as -built map plans. considerations in stability analysis were used and are attached calculations for buttress and shear key. Details of proposed grading and landslide limits on an appropriately scaled and complete topographic, adequate for analysis." This is shown on attached Item.12: "Sections by Stone and Associates indicate variable slide plain dip angles, therefore effects of re -distribution via grading should be considered." In performing analyses for slide stability calculations, a very low angle :'slide plane was used and this was carried from the buttress upslope undercutting the slide section. Since this is below the slide plane, it would eliminate . the variable dip angle. This projection is along the base of the maximum depth of slide as shown by Stone and Slosson in their sec- tions. Accordingly, the projection is a straight line effect, in- creasing the critical plane of the slide whereas irregularities would have a tendency to lock the slide. Therefore, our analysis would assume a more critical condition than actually exists. Item 13: "'A stability analysis of the entire slide must be nerfnrmPel - T— ,, a --- ._T. - Item 13: "A stability analysis of the.entire slide must be performed. In accordance_ wi-th Section 308 of the Building Code, it' muit be shown that their_ is no hazard to proposed structures or adjacent property. We feel that this should be done as a part of the EIR, sine most of the buildable areas are on the landslide. It muss: be shown, that the slide will meet stability stand n itions established by the County. Mere improvement of existing is not satisfactory.' Stability analyses performed for this study will effer.t i°e1y in r. se stability factors for that portion of the slide aba': e --he buttT'rss-shear key. It is our opi.TI.ion that the above c.i._ed aj-.,ticle trom California Geology correctly identifies a slide situat:ior, el, -''where in Diamond Bar; both slides are similar in that the Equestrian Slide is a fossile slide that has been stabilized. Respect fully submitted, „[ :+ E C-f { ON BUENA El.GINEERS, INC. Reviewed and Approved lot H a 11 4 nNorman C. E. 7370 c, . 7 3 LLDJcc-c ion; 4 - Ervin Engineering; Cop, esAeiti-Recrea:: Li =. tsA ENGINEERS, INC. e ey - Des, ;r, rJ .,4 C_ A101 cl.-awn / SC1rle a z LI * /47" Gly t B ,,( -241 '= x j_ = IA'7 = 7 y'tz 6 G Uri r 6z l Uz.11 x o.9 7r kf o, 74 /71 4/ 6 Owl Z rrJf]ZrJrrkr;dice zo /67 x p 2 7 3n • 9! JI2, a 424 Cj.15Y35'1,58y',37007XI76 114 Z so 1F4 g /v 2, 12 Y 0, r- e•Unifs YIW ra;i1$ L)! = D73,75 f --; L, z r e 8 Z T 4177• zz /12 - S • /, 09 Z94, 7-S f Z72,2U DEFINITION: Carbon-14 dating (synonym: radiocar- bon dating). A method of determining an age in years by measuring the concentra- tion of carbon-14 remaining in an organic material. usually formerly living matter, but also water bicarbonate, and other sub- stances. The method, worked out by Wil- lard F. Libby, U.S. chemist (1908- ). in the years 1946-1951, is based on the assump- tion that assimilation of carbon-14 ceased abruptly on removal of the material from the Earth's carbon cycle (such as the death of an organism) and that it thereafter re- mained a closed system. Most carbon-14 ages are calculated using a half-life of 5570 t 30 years, thus the method is useful in determining ages in the range of 500 to 30,000 or 40.000 years, although it may be extended to 70,000 years by using special techniques involving controlied enrich- ment of the sample in carbon-14. From. American Geological Institute GLOS• SARY OF GEOLOGY. 1972 edition. During the past few years, carbon-14 dating methods have been used to deter- mine ages of several large landslides in southern California (Stout, 1969, 1975). The results show that most of these land- slides occurrzd_between ]6.00k3 and 20 o00_vears ago durinQ a .of known heitvy-pcet_tson t hich_ wasn-rtl contetnporaneo_ls wlth WWn. Dread c• _Y- w._ _e_. late Vv isconsinglacial activity-(referred_t_o as Tioga stage in California) and -greatly wered sea level. The heavy precipitation caused faster rates of erosion than at present, and highly saturated ground con- ditions. Lower sea level allowed the stream systems, paniculary coastal streams, to cut down well below present sea level, and this, coupled with high run off resulted in saturated, oversteepened slopes -conditions very conducive to large scale landsliding. ANCIENT LANDSLIDE STABILITY An older age for a landslide does not necessarily indicate a lower risk or a lower likelihood of potential landslide move- ment. Climatic and geomorphic factors usually have a greater effect on subse- quent stability_ Older landslides may have had extensive alluvium deposited against the bottom or toe, thus increasing the sta- Qity, or may have been subject to further erosion and unde_rmining,-in essenez_de- creas i11gtFie—stability. grely, the de- e of_ consolidation is better in older landslides. RADIOCARBON DATING OF LANDSLIDES IN SOUTHERN CALIFORNIA By MARTIN L. STOUT Department of Geology California State University, Los Angeles SAMPLING ORGANIC MATERIALS Radiocarbon dates ranging from 500 to 40,000 years before present (BP) can usu- ally be made on organic materials con- taining carbon ( wood, charcoal, peat, shells, bone). These materials may be as- sociated with ancient slides, and thus pro- vide the means to date the landslide events. However, it is necessary to under- stand the geomorphic changes that occur as a result of landsliding in order to locate organic material which will yield a radio- carbon date closest to the age of landslide movement. In most of the sampling locali- ties described below, the organic matter may contain live rootlets which will con- taminate the sample, resulting in a young- er age. Every effort should be made in the field to avoid this type of sample, particu- larly where there is a large quantity of organic material avaiiable for selection. Stream and Lake Deposits When a landslide of several -tens of acres occurs, it most frequently will move into an established drainage system and may cause local blockage and derange- ment of the main stream course (figure 1). In this case, a pond or lake will usually form on the stream course, and the in - flowing stream will deposit deltaic debris, possibly containing organic materials such aswater -saturated tree limbs and brush. Reeds and other water --loving plants may begin to grow in the pond, and organisms with calcareous shells may thrive. Depending on the nature of the land- slide debris and the regimen of the stream, a pond or lake may be in existence for only a few days or for as long as several hundred years. The longer the lake is in existence, the greater the possibiiity is of organic matter being deposited and pre- served. If organic materials are found in a deposit of an ancient lake which was formed by landslide movement, it is im- portant to know how soon the organic debris wasdepositedafterformationofthelake. The debris closest to the age of movement of the landslide will be found at the bottom of the sedimentary section of the deltaic or alluvial deposits. Organic material higher in the section «'ill be more difficult to correlate with the time of landsliding, and determination of age will usually involve subjective judgment on the rate of deltaic or alluvial sedimenta- tion. After a landslide debris dam is breached, subsequent stream erosion may leave the deltaic deposits preserved as up- stream "terraces". With continued ero- sion, it is possible that these earlier sedimentary layers could be exposed in the bank of a stream gully (figure 1, local- ity A). If this happens, organic material may possibly be obtained without subsur- face trenchingorboringequipment. If blockage of the main channel is followed by rapid breaching of the slide debris dam, it is possible that some org2n c material will be caught up by mudIlOw debris and deposited downstream. Sam- pling and mapping in this type of material California Geology May 1977 . oti Figure 1. Sketch map. of a landslide. established drainage system. showing for carbon-14 dating of landslides. which has moved into an possible sampling areas i POSSIBLE POND OR ALLUVIAL A DEPOSITS UPSTREAM WHICH fWCONTAIN ORGANIC DEBRISDEFLECTED STREAM t I - BSECTIONSHOWN j IN FIGURE 2 r i I i ORIGINAL I i PULL-AWAY ZONE STREAM WITH INFILLED COURSE ORGANIC MATERIAL must be done with extreme care because older, organic -bearing alluvium may also be found in this area giving a much older date than the age of landsliding. Pull -Away Zone Organic materials for radiocarbon dat- ing can be obtained in the pull -away zone sometimes called transverse crack or graben) at the top or head of the land- slide. To obtain samples in a pull -away zone (figures 1, 2, locality 13), it is usually necessary to use equipment for subsurface trenching or boring. During the actual movement of landslide debris, or shortly after, trees or brush may fall into the crack or tumble to the bottom of the slide scarp. Tree limbs, other organic debris, and soil may fall or be washed into the pull -away zone (photos 1, 2d). A pond can also form here with abundant vegeta- PULL-AWAY ZONE —BROKEN ROOTS, INFILLED SOIL WITH BRUSH, LIMBS, POND ROTATED TOE OR HUMMOCKY DEPOSITS, REEDS, SHELLS TERRAIN —POSSIBLE POND ESTABLISH MINIMUM AGE DEPOSITS, VEGETATION OR CALCAREOUS ORGANISMS ORGANIC I ALLU ViUM MAXIMUM SLIDE, BU AGE OF f0- T NOT NECESSARILY MOVEMENT BRUSH OR LIMBS BURIED BY LANDSLIDE MOVEMENT ESTABLISH EXACT AGE OF LANDSLIDE Figure 2. Cross section of landslides sketched in figure 1, show- ing possible sampling areas for dating landslides by the carbon- 14 method. tive growth which would provide organic materials. The organic debris may be pre- served beneath other sedimentary materi- als washed in later. Thus, the best sampling area for age determination pur- poses is near the bottom of the sediments in the pull -away zone. Organic material higher in the section of pull -away zone will again involve subjective judgment on the rate of sediment infilling. Landslide Toe Organic material which will best repre- sent the age of sliding is usually found near the toe or lower portion of the land- slide and is usually buried beneath slide debris. When a slope fails, the debris over- rides and collects organic material grow- ing on the hillside or dead organic material lying near the foot of the slope, which normally is not much older than S k 4it • c _ t'S 4y,. tit :, Y ' fib ` a - '%` z. *r i ad.,:.:-i5k3aita ti`...•.::4.1 - _ ^Tr:i'.bc.:`.. .k- - 4s..a.: Photo 1. Infilled soil shown above dashed line in a pull -away zone of an older landslide in the Puente Formation. San Jose Hills, Los Angeles County. This slide was not dated. but abundant organic material was available in the soil. the landslide movement. Climatic factors that affect the rate of wood decay should also be considered before an age determi- nation of the slide is made. Samples for age determination should be obtained directly beneath the landsiide debris, and preferably near the original boundary between the valley side slope and alluvium of the canyon (figure 2, lo- cality Q. It is usually necessary to obtain samples here with subsurface exploration equipment. If, in the sampling locality, the land- slide had actually reached stream valley alluvium, alluvial and slide debris can be mixed in such a complex manner that it is not possible to determine the original source of the organic material. Thicker sections of alluvium could contain wood possibly several thousand years older than landslide movement (figure 2, locality D). However, undisturbed alluvium con- taining organic materials just under the slip surface would give a fairly representa- tive maximum age of movement for a landslide. On -Slide Ponds and Cracks Organic debris which could be of value in determining the age of sliding may also be found in local pond deposits on the landslide mass itself, with reeds and other vegetation, or possibly shells, preserved in lake bed deposits. If landslide movement caused blockage of local stream tributar- ies in addition to the main channel, or- ganic materials in alluvial deposits pond- ed in those local streams may determine a minimum age. In more complex slides, cracks within the slide mass (not in pull - away zone) may also contain organic matter. 100 California Geology May 1977 UM tf ace._:.....:.`_.c.•,o.f.i-'.L""`:3a'r:.%ii.Z id Bar land - photo 2. Southerly views ofn 9-000 ynaforld bDiailiza on and parko slide show chronology odevelopment. Note same oak trees in each photo. Sai Diamond1972. Bar landslide (below dashed Isnel. Photobby Ft- tress WotStl sample shearofb) Two boys on backwall of shear key - for dating was obtainedlowfillalreadypacedKeyway here w sbackf Iled afterexcava- tion for stability. Photo taken October 1975.(c) Completed overing. Note borrow site cut in upper right; photostabilizationgradtakenJanuary1976.1d1 Upper borrow site cut shows Pull -awayofsecondaryslidemarkeabydarksoilsbungexaminedby geolog'st. The darkerercentageof monders" are c tmoTillon te. let Detail ked soils neros anal higher percentage bedding in the infilled soils- Upper - channel shows homost bed ishighlycalcareous. possibly reflecting high evap- oration rates. Photos taken October 1976. FYes e, le W. . wow r. 1Ve ` fir . 1 ,_ .' .. . .. ,_r:. f., i 4--..Y"z+ a.`r3:RhuafL l..,.a.a. 101 California Gea4o9Y May 1977 2--SJ628 SLIDE/SAMPLE RELATIONSHIPS Materials containing organic debris should be carefully mapped prior to dat- ing in order to determine the exact rela- tionship of the sample to the landslide event. At this point, the degree of infer- ence between sample and event should also be established. Otherwise, misleading interpretations can be made. For example, organic material in alluvium several thou- sand years older than the sliding, or material deposited in a pull -away zone several thousand years after original movement, cannot be used to determine the age of landslide movement. Land- slides may also have several periods of movement and it is very important to de- term;ne which period is represented by the organic material. AGE AND LOCATION OF DATED LANDSLIDES Four landslides have been dated by the author in southern California, and two additional landslides have been dated by others (Stout, 1969, 1975; Morton and others, 1974). The hummocky topo- graphic features of the ancient landslides have been largely obscured by erosion of the slide masses, but scarps are readily discernible. Four of the dated landslides are in coastal southern California, one is in an interior valley, and the other is in the Mojave Desert (figure 3). Diamond Bar Landslide The oldest landslide, dated at 19,075±510 carbon-14 years BP is just off Golden Springs Drive near Sycamore Canyon Park in Diamond Bar, eastern Los Angeles County (f igure 3). In 1975, grading for park expansion and landslide stabilization buried the lower portion of this landslide (photos 2a, b, c). The primary landslide apparently moved along a synclinal axis when the stream in Sycamore Canyon lowered its bed below unstable clays of the upper Mi- ocene Puente Formation. Total move- ment of the main landslide was 80-120 feet as indicated by the width of infilled soil in the pull -away zone at the head of the slide. Secondary sliding above the larger slide covered part of the older in - filled soil, creating a pull -away zone fur- ther up slope (photos 2d. e). During grading operations to construct a compacted fill shear key -buttress, a standard landslide stabilization tech- nique, a large trench" was excavated photo 2b) and small pieces of wood were found in relatively undisturbed alluvium just below the slip surface of the slide. Here, the age of the sample should be con- sidered a maximum age of slide move- ment because the organic material predated the landslide event. Most of the erosion after slide movement approxi- mately followed the original pull -away zone. Deposition of soils within the pull - away zone amounted to at least 13-17 feet of what now appears to be well con- solidated clayey soil. Alluvial deposition against the toe consisted of about 12 feet of sand and cobbles forming a small ter- race. The terrace in turn had been eroded locally with an incised channel about 6 feet deep. Blackhawk Landslide The second oldest landslide is the 17,400±550 year old Blackhawk land- slide, which covers about 5.5 square miles in the Mojave Desert along the northeast- ern side of the San Bernardino Mountains near Lucerne Valley, San Bernardino County (front cover; figure 4). The 1 enesraw 0 SANTA BARBARA ,6 LOS ANGELES O 5 34 LSAN JUAN CAPISTRANO t5T0l11.1969r, I zSAN JUAN CAPISTRANO @1p0.TD4CTII 974T., 3.PAL0S VERDES HILLS 1STOUT,i9691 4.PALOS VERDES HILLS {EML,G,19611 SAN DIEGO -_ DIAMOND BAR dSTWJT,+969t _ - --- GeLACKHAWK LANDSLIDE tSTOUT,19757 1 i Figure 3. General location of landslides in southern California which have been dated by radiocarbon methods. Blackhawk slide is unique because it is the only dated slide located in what is now an and area. Shreve (1968) contended that the land- slide debris, consisting largely of lime- stone breccia from the Paleozoic Furnace Formation exposed on Blackhawk Moun- tain, was the result of a huge rockfall which generated enough momentum to be launched into the air. It then rode upon a low friction air -cushion to its final resting place on gentle alluvial slopes of less than. 3°. Hsu (1975) has taken exception to the air -rafting concept, contending that lo- bate features similar to and including the Blackhawk landslide can be produced by flowage without an air cushion. The age of the Blackhawk slide indi- cates that movement occurred during a period of known heavy precipitation. Therefore, highly saturated ground condi- tions probably contributed to sliding con- ditions. Other landslides in the San Bernardino Mountains, such as the Bar- ton Flats landslide (Stout, 1976a), and many other large landslides throughout the now generally arid Great Basin and southwestern United States probably also moved during this time of heavy precipi- tation, 16,000 - 20,000 years ago. Extensive alluviation from Blackhawk Canyon occurred over the landslide de- bris following slide movement, resulting in the almost complete burial of the tipper portion of the Blackhawk landslide Stout, 1976b). Local depressions farther down on the landslide allowed ponds to form (flat white areas on front cover photo). One pond was at least 7 acres in size, 20 feet deep, and -was subject to rapid deposition of fine grained sediments. Figure 4. General location. Blackhawk landslide, northeast San Bernardino Mountains. See front cover for aerial view. BLACKHAWK LANDSLIDE SAN GABRIEL r MTNS SAN BERNARDINO N MTNS. s SAN 83ERNARDINO 0 10 20 30 miles 102 Californlu Geology May 1977 r Y •„r- J- r R A j Y v r t• c c '- a '+' t''4 -•e,•' •. lit ,...rih. a- aim... ',,..,-_ ..:.e.si'-....r•. • - ._ . colo one ick. lens Photo 3. (a) Lake beds resting re cLlhewB lyingal7kfeeltofdebris. bedded m caceous siiltstoest The rmudstonecalcareous s largely tmater alcontainspde uls veriz s. There are no fossils present movement ceased. ver; zed during landslide movement and deposited been shortly cutfinr8lackhawk slide debris seinceetf,eof t akehe hbeds ells swereformed.ose to the age Side hslolpes movement. (b) An arroyo 70-100 feet across, underlain bylimestoneslidedebris (to right of truck) are the same lake beds shown in (a). Radiocarbon dating of fresh water gas- tropod and pelecypod shells from one of these pond bed deposits indicates a late Wisconsin age of 17,400} 550 years BP stout,1975). The shells were taken from a 3- foot thick calcareous mudstone rest- ing directly on Blackhawk landslide de- bris (photo 3a). The basal mudstone, without layering, is interpreted as consist- ing of material pulverized during land- slide movementanddepositedbystreamsshortlyafter the slide came to rest. The age oftheshellsdepositedwiththemud - stone is, therefore, probably very close to the time of movemcnt. The pond existed for only a short time before a rapidly growing alluvial apron, derived primarily from the extensive post -landslide erosion of Blackhawk Canyon, reached the basin and filled it with thinly bedded layers of micaceous fine -- grained sediments (photo 3a). The absence of evaporite minerals in the sedimentary section suggests the pres- ence of a perennial lake. The stream draining the basin finally breached the landslide debris exposing the entire lake bed section by cutting an arroyo about 70-100 feet across and 25 feet deep. The channel now provides easy1 drive access to the lake beds (photo 3b ) San Juan Capistrano Landslides 750 A.large landslidedatedat1'1,180 4- years BP (Stout, 1969), is in the Capis- trano Formation about 1.5 miles south- east of San Juan Capistrano (figure 5, slide 1 ). The landslide debris has been extensively eroded since movement, re- sulting in some gullies being cut at least 41 feet deep (photo 4). About 35 feet of allu- vium has been deposited against the toe or bottom) of the slide, in effect buttress- ing the slide mass. The presence of this alluvium suggested, even before the radio- carbon date was obtained, that sea level had to have been considerably lower at the time of the landslide event (Stout, 1969), The rise in sea level, subsequent to landslide movement, possibly coupled with drier climate, caused deposition of alluvium in San Juan Valley and its tribu- taries.. Another landslide about 2 miles northeast of San Juan Capistrano in the Capistrano Formation (figure 5, slide 2) has been dated at 10,880± 160 years 11P his land - Morton and others; 1974). slide is a long, lobate mass with gullies measuring as much as 25 feet ir. death eroded into the slide mass. Gradingtflr agricultural purposes has comp y obliterated the upper portions of the slide. The organic material is described as "a carbon -rich soil horizon which was over- ridden by a large landslide" (Morton and others, 1974; p. 5). However, several sec- ondary landslides above the sample local- ity, are even now still active along the edge of theoriginalslidemassinthisval- N LOS ANGELES AL DES ORANGE',. COUNTY HILLS ` SANTA ANA LONG BEACH SCALE SAN JUAN zO 10T ° 20 CAPISTRANO Figure 5. General location of landslides nearSan Juan Capistrano and in the Palos Verdes HMIs. ley. Without subsurface exploration, it cannot be determined whether the organic material represents soil buried by original slide movement, soil developed on back - filled alluvium, or soil developed after the original slide movement, but prior to renewed movement of the peripheral landslides. Palos Verdes Landslides Two landslides have been dated on the southern side of the Palos Verdes Bills figure 5). The slides are 0.5 mile apart and their age difference is about 13,500 year*. The time ip.terval, as related to tl`e present geomorphology of the two slides, gives perspective tolong-term rates of erosion and depositionwithinthePalosVerdesHills. The older slide ( figure 5; photo 6)un- derlies a large portion of Palos Verdes Drive Bast near its intersection with i'alns Verdes Drive South. Organic material in alluvium ponded behind the slide gave a minimum age of 16,200 ± 240 Years B P p L Ehlig, unpublished report. 1967). Several terrace -like levels on this slide suggest possible periodic movement photo 5). The slide is believed to have moved on bentonitic tuff within the Alta Mira Member of the upper ;4iocene ;`fon- terey Formation (Ehlig, personal com- munication, 1969). The younger slide ( figure 5, slide 3) was dated 2915± 205 years BP (stout, 1969). The recency of movement is shown by the lack of erosion on the slide scarp and within theslidemass. Althoush enough slope wash had occurredtofill Ill depressions with loose and poorly solidated debris, the pull - away _10" «as still clearly defined topntraphically before grading buried the slide inabs. California Geology May 1977 103 CLIMATIC SVGNIFICANCE Where glacial chronologies are well es- tablished with radiocarbon dates, a glacial maximum (furthest advance of glaciers) is usually noted between 15,000-20,000 years ago (Suggate, 1965; Wright and Frey, 1965; Easterbrook, 1969, 1973). As noted above, the radiocarbon dates of most ancient landslides in southern Cali- fornia coincide with that age range. This most recent glacial advance in California is known as the Tioga stage. It also represents a time of greatly lowered sea level and generally wetter climate. Most scientists agree that sea level was at least 4W feet lower during the j ioga than it is at.present (Curray, 1969; Curray and others, 1970; Guilcher, 1969). Some data suggest that it was at least 575 feet lower than present (Veeh and Veevers, 1970). Precipitation data for southern Califor- nia have been determined from studies of flora from the La Brea tar pits in west Los Angeles (Templeton, 1964; personal com- munication, 1968). These data suggest that precipitation during a 44-year e.rcle about 14,000 years ago was occasionally 5 times higher than the present mean annu- al precipitation rate in Los Angeles, with the mean annual precipitation for a 40 year period more than twice what it is at present (table 1). Glacial melting, with increased humid- ity, filled many lake basins in the Mojave Desert and Great Basin. For example, the Photo 4. View eastward, showing 17.000 year old landslide(be4ow dotted l,ne).just south of San Juan Capistrano, Orange Counly.Sample used for age determination camefroma boring located near the truck right center). ` last filling and spillover of the ancestral Great Salt Lake (Lake Bonneville) oc- curred about 14,000 years ago (Morrison, 1975). These lake basins are mostly playas today. Comparing the volume of oceanic wa- ter lost during the lower sea level of the late Wisconsin glacial stage with the gla- cial maximum at that time leads to the conclusion that considerable water was tied up in the near surface sediments and that they were probably saturated (Dill, 1969). This saturated condition coupled with increased precipitation probably caused more rapid rates of erosion and oversteepened slopes, forming an ideal setting for landslides, h-.zr-c Photo 5. View northwest, showing 15,OW year old landslide in Palos Verdes Hills. Los Angeles County. Sample for dating was obtained just up stream from pipe bridge span- ning canyon (right center). Grading is for Palos Verdes Drive East which winds up the surface of the slide. ram y • .,''+.} - Photo 6. Oblique view of 2900 year old landslide (center); grading is underway. The sample for dating was obtained from the canyon on lower right side of landslide. Photo byJ. McNey. This late Wisconsin glacial climate was not unique to coastal or high mountain areas. In the United States, heavy precipi- tation during that time probably accounts for many of the large scale ancient land- slides in Arizona, Nevada, New Mexico, and Utah, areas which are generally and regions today. Rates of local erosion were almost certainly significantly increased then with this higher total precipitation. Precipitation and erosion rates probably decreased about 5,000-7,000 years ago, as reflected by a slower rise of sea level since then (Curray, 1969). There is still much to learn regarding glacial -interglacial paleo-climates. De- tailed studies of pollen (palynology), cou- 4t, it a 104 California Geology Mcy 1977 Comparative precipitation values in Los Angeles. 1877 to 1966 and approximately 15,000 years B.P.' Pp[. Ppt• Year Pvt. Year(inches)Year(inches)B.P.(inches) 10 20 30 40 1966 12.91 1965 26.81 1964 7.98 t963 12.31 1962 15.37 1961 5.83 1960 9.57 1959 6.23 1958 17.49 1957 13.24 1956 13.62 1955 11.59 1954 13.69 1953 4.08 1952 24.95 1951 14.33 050 7.38 1949 10.63 1945 7.59 1947 4.11 1946 16.22 1945 12.7E 1944 17.4! 1943 22.5; 1942 7.4( 1941 31,2E 1940 20.2E 1939 12.0t 1938 27.11 1937 17.9 1936 1 B.2 1935 14.4' 1934 14.6 1933 18.7 1932 '10.7 931 1v n 1930 13.0 1929 8.3 1928 8.E 1927 18.E 1926 18.`. 1925 8.5 1924 6.1 1923 6.; 1922 15.: 921 19.85 920 II.I8 919 8.82 918 17.49 9t7 8.45 1916 23.29 1915 16.67 1914 23.21 1913 17.17 1912 9.78 1911 17.85 1910 4.89 1909 23.92 1908 13.74 t907 15.30 1906 21.46 1905 19.19 t904 11 .88 1903 14.77 19C2 13.12 1901 11.96 t9oo 11.30 1899 7.91 1898 5.55 1897 7.0E 1896 16.8E 1895 8.5i 1894 16.1 1893 6.7, 1892 26.2' 1891 It.8' 1890 13.5 1889 34.8 1688 19.2 1887 13.8 1896 14.0 1385 72.3 1884 9.2 1883 38.1 1882 12.1 1881 10.4 1880 13.1 t679 70.'. 1 878 1 1 .: 1877 21.1 10 20 30 40 4.861 14,662 14,863 14,864 14,865 14,866 t4,Pb7 14,868 14,869 14,870 14,871 14,872 14,873 14,874 14,875 14.676 14,877 14,878 14,879 14,8Bo t4,881 14,882 14,SB3 t4,884 14,585 14,886 14,867 14,888 14,889 14,890 14,891 14,892 14,693 14,894 14,895 14,996 14,897 14,698 14,899 14.900 20 15 40 20 3n 50 50 40 20 20 40 20 40 40 30 20 20 10 15 15 IC I`. 1`. 4C 2( 2` 2`. 2' 2( 61 7 7, 7 6 5 4 6 e 10 20 30 40 50 60 70 80 Data are based on U.S. Weather Bureau records. and analysis of tree -ring data {Templeton) is from cypress tree in La Brea tar pits. pled with radiocarbon dating, provide the opportunity to obtain these data (Adam, 1967; Hansen and Easterbrook,1974). For practicing geologists and engineers, the estimation of age based on the erosion- al features of fault scarps and landslides, particularly in regions that are desert en- vironments at present, must be evaluated in light of these changing climatic regimes. For example, a present day fault scarp exposed in the Mojave Desert, was probably not there during the Tioga glaci- ation; the feature could not have survived under the climatic conditions of that time. Thus the fault scarp may be no more than 10,000 years old, not 100,000 years old as would be possible under the pre;ent cli- mate of the Mojave Desert. ACKNOWLEDGMENTS Funds for all radiocarbon dating of samples came from National Science Foundation Institutional grants, and all age determinations were made by Geo- chron Laboratories, Massachusetts. REFERENCES CITED Adam, D.P., 1967, Late Pleistocene and recent palynology in the central Sierra Nevada, California: in Quaternary Paleoecology, INQUA, v. 7, p. 275-301. Curray, J.R., 1969, History of continental shelves: in New Concepts of Continental Margin Sedimentation, American Geologi- cal Institute Short Course Lecture Not Lecture 6). Notes Curray, J.R., Shepard, F.P., Veeh, H.H., 1970, Late Quaternary sea -level studies in Mi- cronesia: Geological Society of America Bullctin, v. 81. p. 1865-1880. Dili, A.F., 1969, Submerged barrier reds on the continental slope north of Darwin, Aus- tralia: Geological Society of America, Ab- stracts with Programs, Annual Meeting, P. 48-49. Bsterbrook, D.J., 1969, Pleistocene chronol- ogy of the Puget Lowland and San Juan Island, Washington: Geological Society of America Bulletin, v. 90, p. 2273-2286, Easterbrook, D.J., 1973, Age and extent of the Olympia Interglaciatio n: Geological Socie- ty of America, Abstracts with Programs, Cordilleran Section, p. 36-37. Ehlig, P.L., 1967, South Shores Mobile Home Park, Palos Verdes, California: unpub- lished. Guilcher, A., 1969, Pleistocene and Holocene sea level changes: Earth Science Review, V. S. p. 69-97. Hansen, B.S., Easterbrook, D.J., 1974, Stratig- raphy and palynology of Late Quaternary sediments in the Puget Lowland, Washing- ton: Geological Society of America Bulle- tin, v. 85, p. 587-602. Hsu, K.J., 1975, Catastrophic debris streams Sturzstroms) generated by rockfalls: Geo- logical Society of America Bulletin, v. 86, p. 129-140, Morton, P.K., Edgington, W.J., and Fife. D.L., 1974, Geology and engineering geologic as- pects of the San Juan Capistrano quadran- gle, Orange County California: Caiif6mia ! Division Mines and Geology, Special Re- 41 port 112, 64 p. Shreve, R.L., 1969, the Blackhawk landslide: y Geological Society of Arnenca, Special Pa- per 108, 47 p. Stout, M.L., 1969, Radiocarbon dating of land- slides in Southern California and engineer- ing geology implications: Geological Society of America, Special Paper 123, p. 167-179. Stout, M.L., 1975, Age of the Blackhawk land- slide, Southern California: Geological Soci- ety of America. Abstracts with Programs, p. 379-379. Stout, M.L., 19763, Barton Flats landslide: in Geologic Guide to the San Bernardino I '/ Mountains, southern California, AEG V Spring Field Trip - 1976, p. 67-Eii7. Stout, M.L., 1976b, Age and engineering geo- logic observations of the Blackiuiwk land- slide: in Geologic guidebool: to southwestern Mojave Desert rceion, SOull" Coast Geological Society, P. lo4-109• Suggate, R.P., 1965, Late Pleist-enc geology of the northern part of the SCUth Island, New Zealand: New Zealand Geological Survey Bulletin 77, 91 p. Templeton, B.C., 1964, The fruits and seeds of the Rancho La Brea Pleistocene Deposits, unpublished Ph.D. thesis, Oregon Stale University. Veeh, H.H. and Veevers, J.J., 1970- Se" level at 175 m off the Great Barrier Recl 13,600 to 17,000 year ago, Nature, v. 226, P. 536- 537, Wright, H.E., Jr., and Frey, D.G., 1965, The Quaternary of the United States: Princeton University Press, 922 p. 'SZ California Geology May 1977 105 DRILLED July 14, 1964 B O R IN G I BY Rotary Bucket SURFACE ELEVATION 7111 DIAMETER 2011 DATU M GEOLOGICAL z O ENGINEERING TEST DATA CLASSIFICATION o- CLASSIFICATION AND M-D--O DESCRIPTION J o N DESCRIPTION D) w cn TOPSOIL 10 CLAYEY SILT (NIL), dark gray, 14.2- 92 soft to firm. Large amount of sand. 12.3- 97 STREAIYI DY CLAY (CL) , black, SA medium a DEPOSITS a. firm. 19.2-103 x: i 10 27.6- 93-c k 00 Seepage, gray, gritty, wet. WEATHERED l CLAYEY SAiTD (SC) , gray and 21-7-108 PUE21TE qr and tan, m. edium firm. C FORMATION I Tan colored, moist, firm. 20 19.3--110 O X 25 Bottom of boring at 251. No caving. Water @ 121. o Boring backfilled. LOG OF BORIN G LEGEND ON PLATE A-2 JOB NO.4513 GEOTECHNICAL CONSULTANTS, INC. PLATE A-1-I DRILLED Jury 14 A 1964 BY Rotary Bucket DIAMETER 20" BORING Z SURFACE ELEVATION 716' D A T U M GEOLOGfCAL ` z CD J o Uj ENGINEERING CLASSIFICATION j CLASSIFICATION AND DESCRIPTION J o y a DESCRIPTION Lis FFILL E.black, mL) , gray, firm. CL) black, TOPSOIL irmS-LREAM CL), gray to DEPOaITS oist, medium furl. Gritty 9 I4z' Seepage ILTY CLAY CL , gray,mottled plastic, soft. MMM TEST DATA DM ^( D)_ D 13.3-110 CP AL EX i8.3--1o8 27.5- 99 27.3-100 Sandy streak 20 AiIDY CLr.Y (CL) , graY, plas tz , medium firm. 28.8-- 95 MAY (CL) , gray --green, Mottled, plastic, medi= 25 , firms. 28.6- 95 30 Bottom of boring at 33'. PTO caving. a t Yr ^-t . LOG OF BOR« G I LEGEND ON PLATE A-2 I 3 .SOB NO, 4513 GEOTECHNICAL CONSULTANTS, INC. PLATE A-I.2 DRILLED July 15, 1964 BY Rotary Bucket DIAMETER 20" BORIN G 3 SURFACE ELEVATION 720' DATU M GEOLOGICAL z o J o ENGINEERING CLASSIFICATION Q CLASSIFICATION AND DESCRIPTION LU o a ESCRIPT10N w v' FILL SILTY SAND (SM), gray, medium firm. 715 TOPSOIL STREA14 DEPOSITS 1 R 20 E7 i C r Y CL , b ack, fig with roots. SILTY CL.Y (CL) , g.r ay-broTrm, mediums firm, slightly sandy. CL."Y (CL), dark gray to black, silty and candy, plastic, medium fzrrl. CLAYEY SAND (SC) , gray, plastic, soft, running water. Fim. er @ 13, . Becoming pore clayey Bottom of boring at 261. Water at 15' . No caving. Boring baGkfilled. TEST DATA DM --( D) 0 9.8--108 21.8- 94 22.4-100 24.0-103 27.8- 97 23.1-102 LOG of BORING LEGEND ON PLATE A-2 i fp-3 ,SOB NO.4513 GFOTECHNlCAL CONSULTANTS, INC. PLF'TE A-1.3 DRILLED July 15, 1964 BORING 4 BY Rotary Bucket SURFACE ELEVATION 725' DIAMETER 20" DATU M GEOLOGICAL o = O w ENGINEERING TEST DATA CLASSIFICATION Q a~ a CLASSIFICATION AND M-D-O DESCRIPTION J o 2 DESCRIPTION D) w t" FILL SA_TFDY SILT YIL buff, loose. TOPSOIL SA-•IDY CLAY (CL) , black, 22.0--100 silty, medium firm. 0 921.3-106 STREAM DEPOSITS SILTY CLAY (CL), Gray and black, mottled, Lardy, medium firm, moist. CLAYEY SAND (SC)., gr ay-bro:,m, 1 medium firm. 19.2-105 SILTY CLAY (CL) , dark bro-im, gritty streaks. N SANDY CLAY (CL) , gray and tan, medium firm. Sandy streaks. Bottori of boring at 261. Water at 121. 1•10 caving . Hole backfilled 23.1-101 23.1-105 25.6- 97 LOG OF BORING LEGEND ON PLATE A-2 i P-3 JOB Na.4513 -_ GEOTECHNiCAL CONSULTANTS, INC. PLATE A-l•4 DRILLED July 15, 1964 B 0 RA is G 5 BY Rotary Bucket SURFACE ELEVATION 729' DIAMETER 20" DATU M GEOLOGICAL J o ENGINEERING TEST DATA CLASSIFICATION a a~ CO 0. CLASSIFICATION AND M-D -O DESCRIPTION w o >- < DESCRIPTION D) LLJ TOPSOIL SILK SAIM (Sm) , gray, firm. 7.6-107r STREAM DEPOSITS SANDY SILT iy1L , light bro,m, SANDY CLAY (CL), gray -brown, 14.4-lOQ moist, firn, mottled. M Light bro .,;r., f i-2M . 7_ Sand and gritty 9 14, ,Prater 10 20 25 Brot•m, wet, plastic, medium firm. Large amount of sand. Bottom of boring at 261. No caving. Water C 12' after 1 hour. Boring backfilled. 21.6-104 23.8-101 25.1- 99 26.0--•100 LOG OF BORIN G LEGEND ON PLATE A-, JOB NO.45I3 GEOTECHNICAL CONSULTANTS, «c. PLATE A-1-5 DRILLED July 15, 1964 BORIN G f BY Rotary Bucket SURFACE ELEVATION 727' f DIAMETER 20" DATU M GEOLOGICAL 2 J o w ENGINEERING TEST DATA CLASSIFICATION m CL CLASSIFICATION AND M_D -0 DESCRIPTION J o r < DESCRIPTION D) w TOPSOIL SANDY SILT (MIL), dark gray, 2 7-7 firm. Z4.2-- 92 ST=1M DEPOSITS 5 QiVIi Y CLAY (GL) , with shale 14.4-io4--mlchips, bro-vn, plastic, f irri . 10 18.2-106 1 Mottled brown and gray, nedium firm. 15 _ Sandy streak, rurming water.33.5- 88 10 20 . J.: ;; 24.6-104 705 25 _: , 25.5- 98 Bottom of boring at 26}. No ca.vingr. Water at 141. Boring backfilled. LOG OF BORING LEGEND ON PLATE A-2 JOB NO.4513 GEOTECHNICAL CONSULTANTS, INC. PLATE A-1.6 DRILLED July 15, 1964 B O R IN G 7 BY Rotary Bucl,Lct SURFACE ELEVATION 724, DIAMETER 20" DATU M GEOLOGICAL Z J o w ENGINEERING TEST DATA CLASSIFICATION a a~ a CLASSIFICATION AND _ D 0 DESCRIPTION J o DESCRIPTION (D) u TOPSOIL I I Si1NDY CLAY (CL), black, firm. 112,4-111Fl.A4 STREPM DEPOSITS WEATHERED PUF FORMATION Very in- distinct beddin T3.-, - -i - 1 f JOB NO.4513 10 IM S f J.MY CLAY (CL) , bro{m, silty, firm. 16.2--115 AND (SP) , small ,_amount of 8. 1--119 clay, bro.-,m, r ediuzn gr npd firm. sof t, bro.., 19. 6-110S.TDSTOXE, massive. Ba tto: of boring at 16 . No caving. Water at 10P after 2; hour Boring bacicti Alec. LOG OF BORIN G LEGEND ON PLATE A-2 GEOTECHNICAL CONSULTANTS, INC. PLATE A-1 T