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W-0 %A DiVI 0 OPEN FILE REPORT 80-5 SF e4 of coo S &GE GEOLOGY FOR PLANNING: GUADALUPE AND POINT SAL 7 1/2' QUADRANGLES, SANTA BARBARA AND SAN LUIS OBISPO COUNTIESi CALIFORNIA (A report to the California Coastal Commission funded in part under interagency agreement number CEIPG 79-18. Coastal Commission funds received from a Federal Coastal Energy Impact Program Grant number 308 (c) -1) by Richard To Kilbourne M and Lalliana Mualchin CALIFORNIA DIVISION OF MINES AND GEOLOGY 1416 Ninth Street, Room 1341 Sacramento, CA 95814 WASTAL ZoNp APPROVED: INFORMATION CENTER @W,james F. Davis State Geologist This publication was prepared with financial assistance from the U.S. Office QE of Coastal Zone Management, National Oceanic and Atmospheric Administration, 90 un4er the provisions of the Federal Coastal Zone Management Act of 1972, as .S26 amended, and from the California Coastal Commission under the provisions of K11 tt*a Coastal Act of 1976, 1980 *Geologist, California Division of Mines and Geology, San Francisco District Office, Ferry Building, San Francisco, 94111 **Seismologist, California Division of Mines and Geology, Sacramento District Office, :Z815 0 Street, Sacramento, 95816 `oL PO-* RE K.4 Y UA F STATE OF CAILIFORNIA EDMUND G. BROWN JR. GOVERNOR THE RESOURCES AGENCY HUEY D. JOHNSON SECRErA R Y FOR RESOURCES DEPARTMENT OF CONSERVATION PRISCILLA C. GREW DIRECTOR DIVISION OF MINES AND GEOLOGY JAMES F. DAVIS s TA 7,E GEoL ows r LIORARY Ce Coastal Commission 6.1' loward "h A. Sai@ :- ancisco. C C J T11 OPEN FILE REPORT 80-5 SF GEOLOGY FOR PLANNING GUADALUPE AND POINT SAL 7 1/2' QUADRANGLESj SANTA BARBARA AND SAN LUIS OBISPO COUNTIESo CALIFORNIA Ln (A report to the California Coastal Commission funded in part under interagency agreement number CEIPG 79-18. Coastal Commission funds received from a Federal Coastal Energy Impact Program Grant number 308 (c) -1) --9 by Richard T. Kilbourne M and Lalliana Mualchin CALIFORNIA DIVISION OF MINES AND GEOLOGY 1416 Ninth Street, Room 1341 Sacramento, CA 95814 APPROVED: James F. Davis State Geologist This publication was prepared with financial assistance from the U.S. Office of Coastal Zone Management, National Oceanic and Atmospheric Administration, under the provisions of the Federal Coastal Zone Management Act of 1972, as amended, and from the California Coastal Commission under the provisions of the Coastal Act of 1976. *Geologist, California Division of Mines and Geology, San Francisco District office, Ferry Building, San Francisco, 94111 **Seismologist, California Division of Mines and Geology, Sacramento District Office, 2815 0 Street, Sacramento, 95816 TABLE OF CONTENTS LIST OF FIGURES AND PLATES ......................................... ii LIST OF TABLES .................................................... iii ABSTRACT ........................................................... iv INTRODUCTION ........................................................ 1 GEOLOGIC SETTING .................................................... 2 PREVIOUS WORK ....................................................... 4 GEOLOGIC HAZARDS .................................................... 5 1. Fault surface rupture ...................................... 5 2. Potential earthquake faults ................................7 3. Historic seismicity ....................................... 11 4. Recurrence of earthquakes ................................. 18 5. Maximum credible earthquakes .............................. 20 6. Ground shaking ............................................ 22 7. Slope instability ......................................... 23 8. Seismically induced liquefaction .......................... 23 9. Flood inundation .......................................... 25 10. Tsunami hazard ............................................ 27 SELECTED MINERAL AND GEOLOGIC RESOURCES ............................ 30 1. Fossil fuel production ................................... 30 2. Ground water recharge ..................................... 32 44 3. Diatomite deposits ........................................ 35 4. Unique geologic features ................................... 36 ACYNOWLEDGEMENTS ................................................... 43 REFERENCES CITED ................................................... 44 LIST OF FIGURES AND PLATES Page FIGURE 1 Major Structural Provinces ................................ 3 FIGURE 2 Larger Earthquakes of Pre-1900 Period .................... 12 FIGURE 2A Epicenters of 1927 Lompoc Earthquake ..................... 17 FIGURE 3 Cumulative Frequenc'Y'Distribution of Earthquakes ......... 19 FIGURE 4 Map showing Commercial Oil Fields of the Santa Maria Province ........................................... 31 FIGURE 5 Hydrographs of water level in wells, Santa Maria Hydrologic subunit ....................................... 33 PLATE la Geology for Planning: Guadalupe 7 1/2 Minute Quadrangle(Geologic Hazards and Resources) ...... (in pocket) PLATE lb Geology for Planning: Guadalupe 7 1/2 Minute Quadrangle (Hydrologic Hazards and Resources) ... (in pocket) PLATE 2a Geology for Planning: Point Sal 7 1/2 Minute Quadrangle (Geologic Hazards and Resources) ..... (in pocket) PLATE 2b Geology for Planning: Point Sal 7 1/2 Minute Quadrangle (Hydrologic Hazards and Resources) ... (in pocket) PLATE 3 Epicenter Map of Earthquakes CM -> 3) within 120 km of the center of U.S.G.S. Guadalupe 7 1/2 Minute Quadrangle (1900-1975) ................................... 49 LIST OF TABLES Page TABLE 1 Sources of Faults depicted on Plates la and 2a of Point Sal and Guadalupe 7 1/2 Minute Quadrangles ........................................... 8 TABLE 2 Faults of Probable Seismic Significance to Point Sal and Gaudalupe 7 1/2 Minute Quadrangles ............ 9,10 TABLE 3 Maximum (Credible) Earthquakes ........................ 21 OPEN-FILr REPORT 80-5 SF GEOLOGY FOR PLANNING: POINT SAL AND GUADALUPE 7 1/2' QUADRANGLES, SANTA BARBARA AND SAN LUIS OBISPO COUNTIES, CALIFORNIA ABSTRACT \J Fourteen categories of geologic data of varying importance for plan- ning and zoning are documented in this report for the area of the Point Sal and Guadalupe 7 1/2' Quadrangles. They include: 1. active sand dunes, 2. Quaternary landslides, 3. regions of potential seisnically induced lia .uefaction, 4. unstable slopes, 5. faults, 6. maximum credible around shaking, 7. areas of fossil fuel production, 8. diatomite deposits, 9. 100-year flood plain with levee integrity, 10. 100-year flood plain with levee failure, 11. Twitchell Dam failure flood plain, 12. height of 100- and 500-year distant source tsunami runup, 13. groundwater aquifer recharge areas, and 14. unique geologic features of significant scientific or educational value. iv All categories of data, except maximum credible ground shaking are depicted on 1:24,000 scale quadrangle maps (plates la-b, 2a-b). The report represents a compilation of available published and un- published data and is not the result of extensive field investigation. It is not intended to take the place of geotechnical investigations that would normally precede any specific land-use. It is intended to be use- ful to planners, developers, and reviewers involved in land use Planning. The relative weight of these constraints in the planning, zoning, or site selection process needs to be evaluated by persons familiar with cost- benefit assessments and risk analysis. These processes are not implied in this report. The existence, description, location, and published docu- mentation, and the need for further studies of geologic constraints are presented as a data base for land use planning. v INTRODUCTION The purpose of this investigation is to identify geologic conditions significant to planning in the Point Sal and adjoining Guadalupe 7 1/2 minute Quadrangles. Section 30253 (1) of the California Public Resources Code specifically requires the Coastal Commission to see that new develop- ment "minimizes risk to life and property in areas of high geologic, flood and fire hazard." This report locates selected geologic hazards present in this portion of the coastal zone and will aid in considering this region for the siting of energy or other facilities in the future. This report is primarily an accumulation of presently available published and unpublished data and involves no significant amount of field investi- gation. It in no way is intended to take the place of detailed qeotech- nical investigations normally preceeding site certification and construc- tion for energy facilities. It is intended to identify conditions perti- nent to energy facility siting, provide references and sources of further information, and to identify information gaps. The study was conducted by the California Division of Mines and Geology and was funded jointly by the California Coastal Commission (80%) and the California Division of Mines and Geology (20%). Coastal Commission funds were ultimately derived from a Federal Coastal Energy Impact Program Grant number 308 (C) (1) The area of study was specified by the Coastal Commission as one of many within and adjacent to the California Coastal Zone where geologic hazard studies would be warranted. GEOLOGIC SETTING The Guadalupe and Point Sal 7 1/2 minute quadrangles cover an area near the northwestern edge of the Santa Maria basin (Figure 1). The geo- logic setting of the area of this investigation is that of a Neocene (Late Tertiary/Quaternary) basin in a transitional seismo-tectonic re- gion between the southern Coast and the western Transverse Ranges (figure 1). The basin has been named the Santa Maria basin after the principal town in the area. In the sense described by Woodring and Bramlette (1950), and Dibblee (1978), the Santa Maria basin is an asymmetric, deenly sub- sided Neogene trough, with an axis trending northwest through the Los Olivos area of Santa Ynez Valley, Los Alamos Valley, and the southwestern margin of the Santa Maria Valley. Offshore investigations indicate that this trough extends from Santa Maria Valley northwest offshore and south- west of the Santa Lucia Mountains for more than 320 kilometers (Hoskins and Griffiths, 1971). Under the axial part of this trough, lies a sheared Franciscan and Knoxville basement complex similar to the lithology of the Santa'Lucia Range. Oil well drilling logs indicate that up to 3,500 meters of Neogene sediments overlie this basement. Cross sections of the Casmalia Hills and Santa Maria Valley by Woodring and Bramlette (1950) and of the Lompoc, Orcutt, and Santa Maria Valley oil fields by Krammes and Curran (1959) suggest that the Santa Maria basin contains a major high angle reverse slip fault. This fault was portrayed by Crawford (1971) as the Orcutt frontal fault. 2 0,0 0 C, 1200001 +35 001 0 cap SANIA MARIA C=2 JWT ORCUTT 0 N4, @Isqu., COO) S A N T A B A R B A R A C 0 U N ..SA1v cRer K c :i PURISIMA POINT > = LOS ALAmos SANrA rn 14 84 shy -aft BUELLTON Oct L MPOC r" POINT SOLVANG ... 10 ARGUELLO rRANSVERSE OANCES PRO LAKE a > CACHUMA YNCE POINT -h CONCEPTION S1 -n M 0 -1 CL 0 00 :r3cr 0 @< 0 0 /0 20 Kilometers PREVIOUS WORK Due to the occurrence of valuable mineral resources and the proposed siting of critical facilities (e.g. the proposed Point Conception LNG site and the Diablo Canyon Nuclear site), the geology of the region, in- cluding the Santa Maria basin, has been intensively investigated. A bib- lioqraphy of the region would include hundreds of references. Discussion of all the references is not feasible within the scope of this report. A few references judged to contain useful documentation of geologic con- ditions pertinent to planning are annotated in this section. Woodring and Bramlette (1950) published a comprehensive report on the geology and paleontology of this region as part of a U.S.G.S. study of oil producing districts in California. Their report contains an ex- tensive annotated bibliography that summarizes the earlier geologic pub- lications back to before the turn of the century. Their 1:24,000 scale geologic map on a photo base of the Santa Maria basin conservatively con- tains four categories of reliability in their symbols for both faults and formation boundaries'. Later, Crawford (1971) interpreted the sub- surface structural geology of the Santa Maria basin as it pertains to oil production and reserves of the area. In a study concentrating on the sea water intrusion problems of the Pismo-Guadalupe area, Cummings, et al. (1970) have compiled and correlated much shallow water well data. The resulting maps, cross-sections, and report detail the hydrogeologic relationships of the Pliocene, Pleistocene, and recent strata of the region. 4 The siting of the Diablo Canyon nuclear facility and the proposed siting of the Point Conception LNG terminal, have resulted in the publi- cation of several detailed seismo-tectonic studies of the region. sever- al important articles and an extensive bibliography are found in CD.MG Special Report 137 of the Hosgri fault symposium volume edited by Silver and Normark (1978). In studies conducted for the Nuclear Regulatory commission, Buchanan- Banks, et al. (1978), compiled a recency of faulting map for coastal south central California including the Santa Maria area. In an analysis of geologic/ seismic hazards to the Point Conception LNG terminal site, Dibblee (1978) prepared a report covering the Santa Maria basin for Santa Barbara County. The California Division of Mines and Geology is currently evaluating these and other studies on this same sub- ject. The Final Safety Analysis Report and Appendices for Pacific Gas and Electric Company's Diablo Canyon Units I and 2 Nuclear Power Plant (Earth Sciences Associates, 1974) contains useful geologic/seismic data for a region that includes the Santa Maria basin. I. 'GEOLOGIC HAZARDS 1. Fault Surface RuDture The hazard of fault surface rupture is clearly associated with traces of active and potentially active faults. For the purpose of this preliminary evaluation, a fault is considered active if it can be shown to cut Holocene strata and potentially active if it has not been shown 5 to be overlain by strata at least 1.8 million years old (Pleistocene). Recognition and avoidance of such fault traces are generally the only reliable mitigation of surface rupture hazard. In the evaluation of this hazard for the Point Sal and Guadalupe 7 1/2' Quadrangles, geologic literature was surveyed for map locations of fault traces within the bounds of the quadrangles. Owing to the long known fossil fuel resource of the region, the geologic literature is ab- undant and often emphasizes structural geology. Though more than forty references were examined to evaluate the published details of area faults and the surface rupture hazard, the publications by Woodring and Bram- lette, 1950; Earth Sciences Associates, 1974; Buchanan-Banks, et al., 1978; and Payne , et Ll., 1978, were the principal references used in the compilation. When all this literature is compiled on one map, there is possibly an overstatement of the number of faults. This can happen when a subsurface fault recognized from drill core data is projected to the surface on one map and shown as a subsurface fault on another. It can also occur as the result of a drafting error. If a fault's exist- ence is in doubt from our limited field work and subjective evaluation, it is queried on plates la and 2a. These queries were not in the orig- inal references used in the compilation. Plates la and 2a (in pocket) show the potentially active faults (defined above) compiled for the Point Sal and Guadalupe Quadrangles. No faults defined as active were documented. In spite of the possible overstatement of the.number of faults, it is still highly unlikely that all of the potentially active faults that 6 exist in the area are shown on plates la-2a. To do this would require detailed field studies usually involving trenching, age dating and geo- physical surveys that are beyond the scope of the present study. Table 1 shows references used for compilation of the faults appearing on Plates la and 2a. 2. Potential Earthquake Faults Seismib shaking can severely damage structures unless adequate pre- cautions are taken in site selection and structural design. The infor- mation on which such decisions must be based includes identification and delineation of those faults capable of generating earthquakes. This por- tion of this report is directed toward the identification of faults that are perceived to be potential sources of damaging earthquakes in the Guadalupe and Point Sal 7 1/21 Quadrangles. Table 2 is a list of these faults. The preparation of this list was guided by the philosophy that in- clusion of questionable evidence of fault hazard should lead to proper investigation, whereas omission of such evidence would lead to the infer- ence that no hazard exists. The list was prepared only from examination of geologic literature and not from original field work. When two or more maps exist in the literature with differences in a fault's length or existence, the more conservative (longer) length and the existence (rather than non-existence) were chosen for consideration. 7 TABLE 1: SOURCES OF FAULTS DEPICTED ON PLATES la and 2a of POINT SAL AND GUADALUPE 7@1 QUADRANGLES FAULT NAME NUMBER SOURCE Pezzoni 5a Woodring and Bramlette, 1950 5b Woodring and Bramlette, 1950 Pezzoni 5c Williams and Holmes, (1945) Woodring and Bramlette, (1950) 5d Woodring and Bramlette (1950) Orcutt Frontal 5e Krammes and Curran (1959) Crawford (L971) Earth Sciences Associates (1974) Payne et al., (1978) 5f Earth Sciences Associates (1974) Payne et al., (1978) 5g Earth Sciences Associates (1974) Payne et al., (1978) 5h Earth Sciences Associates (1974) Payne et al., (1978) 5i Earth Sciences Associates (1974) Payne et al., (1978) 5j Earth Sciences Associates (1974) Payne et al., (1978) 5k Earth Sciences Associates (1974) Payne et al., (1978) 51 Woodring and Bramlette (1950) 5m Earth Sciences Associates (1974) Payne et al., (1978) 5n-s Woodring and Bramlette (1950) 8 TABLE 2 FAULTS OF PROBABLE SEISMIC SIGNIFICANCE TO POINT SAL AND GUADALUPE 7 1/21 QUADRANGLES PUBLISHED DISTANCE AND AGE OF PROBABLE LENGTH IN DIRECTION TO STRATA CUT SENSE OF FAULT NAME KILOMETERS SITE (*) IN Buchanan-Banks MOVEMENT SOURCES KILOMETERS et.al., 1978 PEZZONI-CASMALIA- go+ 2.2 NE Holocene high angle reverse, Woodring and Bramlette (1950), LOS ALAMOS-BASELINE S.W. side up Krammes and Curran (1959), (= ORCUTT FRONTAL of Crawford (1971), Dibblee(1978), Crawford, 1971) Hall (1978) SANTA MARIA RIVER- 114 12 SW Late Pleistocene high angle right- Woodring and Bramlette (1950), FOXEN CANYON-LITTLE lateral oblique Worts (1951), Jennings (1959), PINE slip, northeast Dibblee (1966), Jennings(1975), side up Buchanan-Banks, et.al., (1978) BRADLEY CANYON 12 13 W Pleistocene 45* angle reverse, Canfield (1939), Jennings (= SANTA MARIA of northeast side up (1975), Hall (1978) Jennings, 1975) SAN GREGORIO-HOSGRI 400+ 17.5 E Holocene right lateral slip, McCulloch et.al. (1977), oblique N.E. side up Buchanan-Banks, Stal. (1978), Silver (1978) GAREY 25 19 W Late Cenozoic undetermined Jennings (1975), Hall (1978) (= BRADLEY CANYON of Jennings, 1975) OCEANIC-W. HUASNA 120+ 21 W Late Pleistocene high angle, possibly Hall (1973), Earth Sciences left-lateral strike Associates (1974), slip Buchanan-Banks, et.al. (1978) SAN MIGUELITO 20 22 S Pliocene predominantly dip Hall and Surdam (1967). slip southwest Earth Sciences Associates side up (1974), Hall (1978) EDNA 43 23 S Pleistocene high angle dip slip Earth Sciences Associates northeast side up (1974), Buchanan-Banks, et.al. (1978), Hall (1978) Distance to site is measured as closest point on fault to center of Guadalupe 7 1/21 quadranghe (an arbitrary point, not a site location). TABLE 2 CONTINUED SUEY 24 24 W Late Cenozoic high angle dip slip Jennings (1959) northeast side up EAST HUASNA 33 30 SW Late Cenozoic right lateral oblique Hall and Corbato (1967) slip northeast side Earth Sciences Assoclates(1974) up Buchanan-Banks, et.al. (1978) SUR-NACIMIENTO 290 35 SW Late Cenozoic high angle reverse, Page (1970) northeast side up Earth Sciences Assoclates(1974) RINCONADA 300+ 39 SW Late Pleistocene predominantly right Dibblee (1972) lateral strike slip Earth Sciences Associates(19741 SOUTH CUYAMA-OZENA ]Do 42 SW Pliocene reverse, southwest Dibblee (1978) side up LA PANZA 73 47 SW Pliocene reverse, southwest Dibblee (1973) side up SANTA YNEZ-PACIFICA 150+ 47.5 N Late Pleistocene variable dip, left Dibblee (1950) lateral oblique slip Earth Sciences Associates(1970 south side up SANTA LUCIA BANK 135+ 67 E Holocene dip slip Hoskins and Griffiths (1971) Earth Sciences Assoclates(1974 SAN ANDREAS 1200+ 73 SW Holocene right lateral strike Jennings (1975) slip An important data gap exists in this compilation in that no litera- ture was examined showing geologic structure of the offshore area in a 10 kilometer wide belt between Point Sal and Pismo Beach. This area is particularly important, in that it is perpendicular to the regional structure and, if faults exist in this region, they would probably con- nect with existing land based faults or to branches of the presumably active Hosgri fault. This offshore area is currently under investiga- tion by the U.S.G.S. Their analysis is in progress and has not yet been published (July 1, 1980). Information to fill this gap might be obtained upon publication of the U.S.G.S. data, through the purchase of proprietary oil company data, or by conducting independent seismic refraction and reflection surveys. 3. Historic Seismicity Pre-1900 The Guadalupe area probably has experienced ground shaking of dif- ferent intensities, even before recorded historical time, from earth- quakes in central and southern California. The following descriptions of pre-1900 earthquakes in the coastal region from Monterey to Santa Barbara Channel are taken from an on-going investigation of the CDMG earthquake catalog project (Toppozada, et al., 1979) and Earthquake His- tory of the United States (Coffman and von Hake, 1973). These are pre- sented chronologically to show that the Guadalupe area needs careful M 5.8 (1864) M 6.2 (1885) 6MM0853) 8 RF(1830) M 8 (1857) GUADALUPE M 7 1812) M 5.60893) 100 KM 120 KM 150 KM 20OKM PRE- 1900 LARGER EARTHQUAKES FOR GUADALUPE SITE (Post-1900 earthquakes are shown on plate 3.) j 1, evaluation of seismic hazard from coastal earthquakes for siting criti- cal facilities. Figure 2 shows seven larger pre-1900 earthquakes ([email protected]; 1>,Vl MM) from Monterey to the Santa Barbara Channel and plate 3 shows epicenters of earthquakes of magnitude greater than 3 within 120 km of the center of the Guadalupe Quadrangle from 1900 to 1975. The larger area for the epicenter map of pre-1900 earthquakes M:?, 5 is shown on fig- ure 2 because the locations are more uncertain, whereas a smaller region was selected for post-1900 earthquakes. 1812 December 21: Epicenter 34.2N; 119.7W; Magnitude 7.2.(Santa Barbara Channel, damage from Lompoc to San Fernando; Tsunami?) This shock was damaging in Santa Barbara, Ventura, and northern Los Angeles Counties. A strong and damaging foreshock alarmed inhabitants and sent then fleeing from buildings. This, undoubtedly, saved many lives when the main shock occurred. Some people were injured, but there were no deaths reported. The church of Purisima Mission and many of the mission buildings were destroyed. At Santa Ynez Mission, a corner of the church fell, all roofs were ruined, walls cracked, and many new hones were demolished. At Santa Barbara, all mission buildings were severely damaged and the church was later rebuilt. At the presidio, some build- ings were ruined and the remaining structures were damaged. Xt San Buenaventura Mission, the tower was wrecked and much of the facade of the church had to be rebuilt. At San Fernando Mission, 30 beams had to be used to keep the walls from falling. Strong aftershocks occurred un- til February and shocks of less intensity continued until April 1813. 13 This earthquake may or may not have generated a tsunami. A recent examination of evidence for a tsunami by Marine Advisers, Inc. (1965) neither proves nor disproves the occurrence of tsunami waves associated with this earthquake. mission records at that time mention fear of the sea, but give no details. Reports of a tsunami, which do not appear in the literature until many years after the earthquake, are based on the memory of several individuals and are poorly documented. 1830 Date unknown: Epicenter 35.5N; 120.6W. Intensity VIII RF, which is approximately VII-VIII MM. Damage at San Luis Obispo and Santa Margarita. Church was damaged in San Luis Obispo. 1852 December 17: It is doubtful that this event occurred; this conclu- sion is supported by unpublished CDMG research relative to historic Cal- ifornia seismicity and is therefore not shown on figure 2. 1853 February 1: Epicenter 35.6N; 121.IW; Intensity VI RF, which is about V-VI MM. San Luis Obispo County. San Simeon. Violent shocks damaged houses. 1857 January 9: Epicenter 35.3N; 119.8W, Magnitude 8 (San Andreas fault rupture from Parkfield to Cajon; Near Fort Tejon). violent shock. A ground crack 65 km long was observed in the vic- inity of Fort Tejon, an army post about 6.5 km from the San Andreas fault 14 between Los Angeles and San Francisco. Near Tejon, a corral was convert- ed by horizontal dislocation of the ground into an open S-shaped figure; at the Fort, buildings and large trees were thrown down. The roof of the mission church at Ventura collapsed. Artesian wells in the Santa Clara Valley (near Ventura) ceased to flow, and in other places, increas- ed their flow. Several new springs were formed near Santa Barbara. There were large fissures in a number of places. Wood (1955) and Allen (1925) have considered this shock potentially the most destructive in the Coast Ranges since the arrival of Europeans in the region. 1864 February 26: Epicenter 36.5N; 121.5W; Magnitude 5.9, possibly Monterey County. Preliminary estimates of intensity by CDfIG are: V M11 at San Jose, Stockton, San Francisco; VI MM at Monterey and Watsonville. 1885 April 12: Epicenter 36.2N; 120.8W, Magnitude 6.2 (Monterey, San Benito, and Fresno Counties). San Andreas fault M. This shock was felt strongly at Martinez, Santa Rosa,and Healdsburg, and may have originated on the San Andreas fault, in the thinly settled region east of King City, Monterey County, although the actual location is uncertain. Chimneys were thrown down at Las Tablas, 30 miles (48 km) northwest of San Luis Obispo. Slight damage occurred at Salinas, San Luis Obispo, and Monterey; felt to Marysville on the north, keller on the east, and Ventura on the south. Little damaqe. 15 1893 May 19: Epicenter, 34.2N; 119.6W.@ Magnitude 5.8 (Santa Barbara Channel, southeast of Ventura). Felt from San Diego to Lompoc and inland as far as San Bernardino. Highest intensity occurred in the region southeast of Ventura. Duration at Ventura was about 15 seconds. No damage was reported, but it may have been potentially destructive. Probable submarine origin. Post-1900 There were 39 earthquakes of magnitude greater than M5.5 and/or in- tensity greater than VI MM within 120 km of the center of the Guadalupe 7 1/2' Quadrangle for 1900-1975 (Toppozada, et al.,,1978; Real, et al., 1978). Post-1900 earthquakes within 120 km of the center of the Guada- lupe quadrangle include the 1922 Cholame Valley earthquake (M 6.5), the 1925 Santa Barbara Channel earthquake (M 6.2), the 1934 Parkfield earth- quake (M 6.0). and the M6.0 earthquake near Bryson in 1952. For the pur- pose of this study, it is considered that the 1927 Lompoc earthquake is the most significant earthquake for the study area. Hanks (1979) presented the epicenter of this earthquake as deter- mined by several authors and by himself as presented in figure 2A. it can be seen from this ficrure that the epicenter suggested by Gawthrop (1978) is closest to the study area under consideration. None of the suggested epicenters are absolutely correct due to unreliable factors (distribution of seismographic stations, observation of arrival times, etc.) and hence, it would be prudent to assume that a repeated earthquake could be located near or about the same place as was suggested by Gawthrop (1978). 16 Figure 2A. EPICENTERS OF 1927 LOMPOC EARTHQUAKE Sources (Chronological) BYERLY, P. (1930). The California earthquake of November, 1927, Bulletin of the Seismological Society of America, V.20, 53-66. NEUMANN, F. (1931). Seismological report-October, November, December, 1927, U.S. Coast Geodetic Survey. Series 503. ISS (1931). International Seismological Summary for 1927, October, November, December, University Observatory, Oxford. RANKS, T.C., J.A. HILEMAN, and W. THATCHER (1975). Seismic moments of the larger earthquakes of the Southern California Region, Bulletin of the Geological Society of America, v.86, 1131-1139. GAWTHROP, W. (1975). Seismicity of the Central California coastal region, U.S. Geological Survey Open File Report 75-134. GAWTROP W. (1978). The 1927 Lompoc, California, earthquake, Bulletin of the Seismological Society of America, v.68, 1705-1716. HANKS, T.C. (1979). The Lompoc, California, earthquake (November 4. 1927; M-7.3) and its aftershocks, Bulletin of the Seismological Society of America, v.69, 451-462. 17 Ground shaking from such an earthquake would cause significant damage in the Guadalupe and Point Sal 7 1/21 Quadrangles. More study is needed to evaluate ground shaking for such an event. 4. Recurrence of Earthquakes Seismicity data from the CDMG Earthquake Catalog for the period 1900- 1975 (Real, Toppozada, and Parke, 1978) for the area within 120 km of the center of the Guadalupe Quadrangle has been used to estimate the return period of earthquakes using the relation log'f N - a-bM. In this equation, 7N is the number of earthquakes per year of mag- nitude M and greater for the area (about 45,000 square km) considered, and "a" and "b" are constants to be determined from a plot of log,2: N versus M on semi-logarithmic paper. Pre-1900 earthquakes are probably incomplete, especially for magnitudes less than 5.0 and hence are not considered in the recurrence analysis. In the analysis* the seismicity data was normalized with respect to the time period (about 75 years; 1900-1975), but not with the area. The minimum magnitude for the analysis is M3 and it is most likely that mag- nitudes less than M4 are incomplete for the period considered. In future analysis, consideration should be given to completeness of data. The present study is preliminary and subject to revision when complete- ness of data is considered. 18 LOG 10 E N3.17 - 0.72 M SELECTED RECURRENCE TIME YEAR MAGNITUDE 50 6.8 100 7.2 z 200 7.6 Ir w cr w 0- w a D U- 0 cn w Ic cr w U- 0 cr w m z Figure 3. CUMULATIVE FREQUENCY DISTRIBUTION OF EARTH QUAKES -GUADA LU PE SITE TIME PERIOD: 1900-1975 AREA: 45,000 SO. KM. 19 0.01 1 1 1 3 4 5 6 MAGN IT U DE (M) Figure 3 shows the recurrence curve. The constants Na" and "b" are determined to be 3.17 and 0.72, respectively. The 50-, 100-, and 200- year earthquakes are about M6.7, M7.2, and M7.6, respectively. The valuesof these magnitudes might increase slightly when completeness of data is considered. S. Maximum Credible Earthquakes (MCE) A number of methods are proposed in the literature and technical reports for estimating the magnitude of an earthquake that could be associ- ated with a particular fault. Usually, it is assumed that half the fault length ruptures in the event of the MCE (Slemmons, 1977, pp. 111, 116). The magnitudes of MCE in this study are based on equations relat- ing magnitudeand fault rupture length for different fault types suggest- ed by Slemmons (1977) and Mark (1977), and for North America faults by Slemmons (1977) and magnitude and fault rupture area by Wyss (1979). Magnitude and fault rupture length relationship may depend on geo- graphic regions (Acharya 1979). The most recent study relating magni- tude and fault rupture area (Singh et al., 1980) does not change sub- stantially the relationship suggested by Wyss (1979) for interplate earthquakes such as those occurring on faults in this report. 20 Table 3 Maximum (Credible) Earthquakes Bedrock Fault 1/2 Fault Length (Km)' Distance (Km)(*) MCE (M) Acceleration (g) Pezzoni-Casmalia Los Alamos-Baseline 45 2.2 6.8-7.5 0.68-0.73 Santa Maria River Foxen Canyon-Little Pine 57 12 6.9-7.3 0.42-0.45 Bradley Canyon 6 13 5.5-6.9 0.21-0.40 San Gregorio-Hosgri 200+ 17.5 7.5-7.8 0.40-0.42 Garey 13 19 6.0-6.3 0.21-0.24 Oceanic-W. Huasna 60 21 6.9-7.2 0.30-0.33 San Miguelito 10 22 5.8-6.2 0.16-0.20 Edna 22 23 6.4-6.8 0.22-0.27 Suey 12 24 6.0-6.S 0.17-0.22 East Huasna 17 30 6.2-6.7 0.15-0.19 Sur-Nacimiento 145 35 7.3-7.9 0.22-0.29 Rinconada 150+ 39 7.3-7.7 0.20-0.2S South Cuyama-Ozena so 42 6.9-7.5 0.16-0.21 La Panza 37 47 6.7-7.4 0.12-0.18 San Ynez-Pacifica 7S+ 47.S 7.1-7.6 0.14-0.19 Santa Lucia Bank 68+ 67 7.0-7.6 0.09-0.13 San Andreas 600+ 73 7.9-8.4 O.lS-O.19 From center of Guadalupe 7@ quadrangle. At center of Guadalupe 7@ quadrangle. Fault lengths for this report were obtained from data presented in table 2. Dip of faults Me to 96') and focal depths (10 km) correspond- ing to maximum fault depth are assumed for the calculation of fault rup- ture area. Ranges of magnitude of MCE expected from faults are given in table 3. 6. Ground Shaking Seismic waves propagate from sources of the disturban6e in all dir- ections (not necessarily with equal seismic wave amplitude). For engi- neering applications, one is concerned with strong motion experience in the near-field region, which is dominated by high frequency waves. in general, seismic waves are attenuated (diminished) by both elapsed time and distance from the source. Attenuation with distance is called spa- tial attenuation and depends primarily upon the physical properties of the propagating medium. Several studies (for example, Trifunac, 1976; Boore et al., 1980) relate magnitude of earthquake, distance from seismic sources, and ground shaking induced by seismic waves. Due to lack of recorded data, there are widely differing opinions about ground shaking within a few kilo- meters from the seismic sources. For the present site, we may apply the attenuation curves suggested by Schnabel and Seed(1973) because their study was directed to accelera- 22 tion in rock from earthquakes in the Western United States. The bedrock accelerations are shown in table 3 and range from about 0.09 g (Santa Lucia Bank fault) to 0.73 g (Pezzoni-Casmalia-Los Alamos-Baseline fault). These accelerations are estimated for the center of Guadalupe 7 1/21 quadrangle. 7. Slope Instability Three categories of areas of slope instability are portrayed on plates la and 2a. They include: (1) ireas of active sand dunes; (2) areas of Quaternary landslides; (3) areas of steep river bank slopes and of recognized sea cliff instability. Areas of active sand dunes are defined as those regions covered with unvegetated wind blown sand. These areas were compiled from topographic maps of the region and confirmed through aerial photo and field examina- tion. Areas designated as Quaternary landslides were taken from the 1:24,000 geologic mapping of Woodring and Bramlette (1950) and confirmed from examination of aerial photos. One small area of steep river bank slope was defined from closely spaced contour lines and confirmed by aerial photo and field examination. The area designated as unstable sea cliffs was subjectively defined in a similar manner. 8. Seismically Induced Liquefaction Major landslides, lateral movement of bridge supports, settling and tilting of buildings and failure of waterfront retaining structures have 23 all been observed in recent years as a result of seismically induced liquefaction. As discussed in this report, liquefaction describes a phenomenon in which cohesionless sediments lose strength during an earth- quake and acquire a degree of mobility sufficient to permit movements of several meters or more. Three criteria are needed to produce the phenom- enon: (1) water saturation, (2) well- sorted, cohesionless sand or silt-size sediments, and (3) an earthquake. This is necessarily a some- what simplistic explanation, but will suffice for the purpose of recog@ nizing where this hazard has a potential of occurring. When an actual site is chosen, pqrameters such as grain size, sorting, relative density, thickness of strata, confining pressure and recurrence intervals of cri- tical durations of earthquake stress cycles, could be obtained to better predict the likelihood of liquefaction. in designating regions of the Point Sal and Guadalupe 7 1/21 Quad- rangles where liquefaction may occur, the following assumptions and methods were used: a. The region is seismically active and earthquakes of sufficient mag- nitude and duration of ground shaking will occur in the future. These earthquakes would induce liquefaction in appropriate soil conditions. b. These soil conditions occur in non-indurated, well-sorted, sandy and silty sand units, as described on the geologic maps of Woodring and Bramlette (1950). 24 c. Liquefaction could only occur if these sediments were in a saturated con- dition below the water table. d. Liquefaction would probably not occur at a depth greater than 18 meters, due to'high confining pressure below this depth. Using these relatively conservative assumptions, areas of "Old, In- termediate and Modern dunes sand and Alluvium" Oloodring and Bramlette, 1950), where the water table is less than 18 m from the surface (Cummings et al., 1970, and personal communication, 1980) have been designated as regions where liquefaction potential exists. As with the previous sections of this report, we have been guided by the philosophy that it is prudent to include all areas where a poten- tial hazard exists. In general, the liquefaction potential would in- crease in the westerly portions of the quadrangles (shown on plates la and 2a) because of both the shallower ground water table (Cummings et al., 1970 and DWR, 1980, pers. com.) and the increase in the silt and fine sand fraction of the alluvium in this region Worts, 1951). 9. Flood Inundation The Santa Maria River and its major tributaries, the Cuyama and Sisquoc Rivers, have a total drainage area of approximately 4300 square kilometers. This river system is the principal flood hazard to the area 25 of study. The area drained is elongated in an east-west direction. The topographic highs which separate this basin from adjacent drainages in- clude the Caliente Range, the La Panza Range, and Garcia Mountain on the north; and the Casmalia Hills, the Solomon Hills, the San Rafael Moun- tains, Big Pine Mountain, Pine Mountain, and San Guillermo Mountain on the south. The flood hazard for the Guadalupe and Point Sal Quadrangles has been assessed using published estimates of three hypothetical floods. First is the 100-year probable flood. Data for this event were trans- ferred to the Guadalupe 7 1/21 Quadrangle (plate lb, item 1) from the same scale map prepared by the U.S. Geological Survey (1971). This haz- ard was omitted on the Point Sal Quadrangle because of the lack of a pub- lished source of data. This event is delineated through the use of readily available infor- mation on past floods rather than from detailed field surveys and inspec- tions. In the case of the Guadalupe 7 1/21 Quadrangle, portrayal of this flood assumes the flood control levees along the Santa Maria River remain intact. A second hypothetical flood is the case of the 100-year flood, com- bined with levee failure of the flood control levees along the Santa Maria River (shown on plate lb as item 2). The data for this event were obtained from the same source (U.S. Geological Survey, 1971), usinq av- ailable historic flood records. Portrayal of this hazard was, likewise, omitted on the Point Sal Quadrangle because of lack of a published source of data. 26 The flooded area caused by a third hypothetical flood, a catastrophic failure of the Twitchell Reservoir Dam on the Cuyama River, is depicted on plates lb & 2b. This map was prepared in 1975 by the Water and Power Resources Service (former Bureau of Reclamation), and is available from the California Office of Emergency Services. The area of this potential flood, assuming a full reservoir and rapid failure, is shown on plates lb and 2b as item 3. Lines of the estimated time, elapsed from the time of failure to the time of maximum water surface elevation, are shown on the maps. Both, the travel time and the elevation of the water surface would change appreciably with any variation in assumptions related to mode of dam failure. The following assumptions were made by the Water and Power Resources Service: a. The reservoir would be full, b. Twitchell Dam would be breached at the deepest point, c. The breach would take the form of a steep sided parabola, d. The breach would erode to near streambed in the time it would take for the reservoir to lose one-half of its volume, e. Maximum discharge would be produced when the reservoir loses one-half of its volume, and 3 f. Potentially damaging downstream flow equals 2832 m /s. 10. Tsunami Hazard Hazards from tsunami inundation are difficult to assess for the Point Sal area because of the short historical record and the lack of 27 definitive literature on this subject. At least five tsunamis (with a probable runup >.1.0 in) have occurred in this region since 1812. They include: 1812 (local generation), 1927 (local generation), 1946 (Aleutian trench generation), 1960 (Chile-Peru trench generation), and 1964 (Gulf of Alaska generation). The 1812 event is documented only from reports from early Spanish missions, and the precise amount of runup for this event is not known, but it is generally considered to be major. The 1927 tsunami produced a 1.8 meter wave at both Pismo and Surf (27 km north and 23 km south of Point Sal, respectively). The 1946 tsunami produced a runup of 1.2-1.5 m in San Luis Obispo Bay (Pismo?). The 1960 Chilean and the 1964 Alaskan earthquakes likewise produced tsunamis that reached the Point Sal region of the California coast. No runup data was found specifically for Point Sal, nor was any damage for the Point Sal area reported for any of these tsunamis. This is best explained by the fact that there has never been any significant population of settlers in this region. A recent study by Houston and Garcia (1978) represents the state- of-the- art in assessing the 100-and 500-year probable (distant source) tsunami runup. This study includes the Point Sal region of the California Coast. Their calculated runup values include the effects of astronomical high tide and the shoreline configuration. Their results compare well with the variations in the runup for the different locations on the Cal- ifornia coast observed in the 1964 tsunami. Their values for the 100- year and 500-year tsunami runup are sho%,m on plate 2b and as item 4. These values do not include meteorological high tide (storm surge) nor storm waves, so a tsunami that arrived during a once-ver-year storm woulA 28 probably have additional height. Assuming 0.3+ m storm surge and 3.8 m storm wave height, similar to that projected for Diablo Canyon Nuclear Power Plant by Earth'Sciences Associates, 1974, this addition would yield a total wave height of 4� m. An important information gap exists in this assessment of tsunami hazard, in that only distant source tsunami recurrence and runup values were calculated by Houston and Garcia (1978). Of the five historic tsunamis of probable wave height greater than I meter known to have occurred, only three were of distant origin. Both of the two tsunamis of local origin were higher in runup than the three distant source tsunamis. It appears that locally generated tsunamis present a greater hazard to the area of this study than distant source tsunamis. Hammack (1972) has shown that near the generation area of a tsunami, details of ground motion during the earthquake and details of the permanent deformation of the seafloor influence the form of the resulting tsunami. According to Houston and Garcia (1978), "accurate predictions of the properties of locally generated tsunamis are not possible at this tine". For the pre- sent study, no attempt was made to predict the precise runup hazard from a locally generated tsunami. The offshore extension of the Pezzoni- Casamalia-Los Alamos-Baseline fault because of its apparent activity, sense of movement, and location relative to the area of investigation, is a prime candidate for such an investigation. 29 In spite of Houston and Garcia's negative assessment of reliability of such studies, some hazard assessments have been made in this area. Earth Science Associates (1974), in studies done for the Diablo Canyon Nuclear Power Plant, have presented a detailed analysis of locally gen- erated tsunamis for the Diablo Canyon area. A 9.14 m design basis sea water flood level was accepted by the NRC (1976). 11, SELECTED MINERAL AND GEOLOGIC RESOURCES 1. Fossil Fuel Production The Guadalupe and Point Sal Quadrangles lie entirely within the well- explored and highly productive Santa Maria oil province (figure 4). In 1971, it was estimated that 100-600 million barrels of oil still remain to be found in the province mostly in the central area and near the northern and northeastern provincial borders (Crawford, 1971). Most of this oil is expected to be produced from already discovered fields, as no significant fields have been discovered since 1952 (Crawford, 1971; DOG, oral communication, 1980). Some of the reasons why commercial oil fields have been considered potentially in conflict with the siting of other facilities include: a. The fire hazard associated with oil producing operations. 30 Luis @Spo &W 0 00 20 KK 4, SAIII LUIS "o .0 -8 0 t -35 p od PT SAL 0 7e< Is ""I. -S 'kis OT *NAWCAMLLO @Ivk PT SANTA "RBARA CONC.Eprold Figure 4 MAP SHOWING COMMERCIAL OIL FIELDS OF THE SANTA MARIA PROVINCE Vertically hachured areas are oil fields; solid black areas Jurassic - Lower Cretaceous outcrops; open circles are wells that penetrated "effective basement." (From Crawford, 1971) 31 b. Differential settlement and the potential reactivation of faults due to fluid withdrawal associated with oil production. c. Induced seismicity associated with secondary recovery methods such as steam injection (usually micro-seismicity when compared to the region- al seismicity of this province). d. The loss of petroleum resources if production is stopped to mitigate the previous three problems. All of these potential reasons for conflict are directly associated with the oil fields and are not regional in their effect. Severe settle- ment problems, such as those that have occurred in the area of Long Beach, have not been reported in the literature for this area. This could be due to lack of study of this problem in the Santa Maria Province. Second- ary recovery methods using steam injection are being used in the fields on the Guadalupe and Point Sal Quadrangles (DOG, oral communication, 1980, and field observation). Areas of known present day fossil fuel production are shown on plates la and 2a as item 6. 2. Ground Water Recharge The entire study area, especially the Santa Maria Valley, is devot- ed primarily to agricultural use. 37% of this land within the Coastal Zone on the Guadalupe 7 1/2'Quadrangle is irrigated, presumably by ground water. Because of this, ground water becones a very valuable mineral resource. According to hydrologic studies (Cummings et al., 1970), the 32 1*45 is4o 104T 11040 4040 toga I tost tou toga 10444 too% toga Ito a? Ito&* IS&* toga Im I too* Ito& too 4 toga 1*441 pw Its%% so to 44 40 j 'vvv x so v `L04 so DEPT 14 KAMA PIERPOPINTto STATE WELL MONS N FEET IN FFEET Eft rv V Ilkw/ -wl ns 00-444 aw - N I I I I -T UMKP Ac"r LINE VATE WILL DEPTH PCPFO04ATIONS pt"FORATEF To MINI 1614ENQ NUMSER IN FEET IN FEET AOUIPICR -IIN/35*-3301--14t 135-141 001L 01; as so lownw-allml 1?$ 21:311: OPPA-8 00 fi L so 40 A 40 A N J) Oil i IN 30 v 'kil U I T4 V -0 vvv v v to v U v ILV so so @J Vi A A 40 so vl\ / 'A 30 I V w to STATEWELL j,NEPTK JPEAFORATiONSIPERFORATED@-- to w WOBER FEET IN FEET AQUIFER U. tON/35W-TFII 24 0 IGO,, -OPTA I Z ?a ?a so so 0 50- so At > 40 40 OF STATE -J PERIOD WELL DEPTH IPERFORATIONS PEFIFORATE.L-- W So RECORD "LAWR IN FEET I IN FEET AOUIFER 30 1 1110::19 'q 1945-1956 ION/350-9FI 198 52 95 001L w 20 1959- ION/350-9FI* - 400 1 228-240 20 C.) I WELL DEEPENED JANUARY 1959 di so so ix 70 70 I L cr to so w A A ]SO 50 U v q R A 40 40 -STATEWELL DEPTH PERFORATIONS PERFORATED NUMBER IN FEET IN FEET AOUIFER v N U V t02-106 34-136 30 10141,35110-21114 310 :45-175 OGIL-OprA-v re 246:248 251 300 952 1195311 1966 11967 ligse I IT .",!1 -5 -1-711964 11965 1 1949 11950 11951AI 954 11955 __1956 1.5-1 r1l It .959 STAY @EE NUM W LL BER 9" J14 1 Figure 5. HYDROGRAPHS OF WATER LEVEL IN WELLS - SANTA MARIA HYDROLOGIC SUBUNIT DEPARTMENT Of WATER RESOURCES. SOUTHERN DISTjiCT. 1969 after Cummings, It al., 1970) 33 area north of the Casmalia Hills, in the Guadalupe Quadrangle, is part of the Santa Maria hydrologic subunit. There are already problems in this hydrologic system - ground water level decline and salt water intrusion. Water level measurements in wells from 1945-1968 (Cummings et al., 1970) show a decline in the ground water level of this aquifer subunit (figure 5). The cause of this decline is considered to be the heavy pumping for irrigation. Salt water encroach- ment is already beginning to be a problem. Increases in groundwater use or decreases in fresh water recharge to the system would allow greater encroachment. The principal recharge of ground water to this aquifer system occurs at the surface outcrops of the Paso Robles Formation on the north flank of the Casamalia Hills. For this reason, the area of outcrop of the Paso Robles Formation on the Guadalupe 7 1/21 Quadrangle has been portrayed as a valuable geologic resource on Plate lb (Item 5). As the quantity and quality of the groundwater in this hydrologic subunit decreases, the value of this mineral resource will increase due to an assumed constant or increasing demand for water in this agricultural region. Any major development in this region should require further study of the impacts by a hydrologist. The hydrology of the region has been studied by Cummings et al, 1970 and is being monitored by the California Department of Water Resources. 34 3. Diatomite Deposits Portions of the Guadalupe 7 1/21 Quadrangle contain extensive de- posits of commercial quality diatomite. Based on the assumption that any high value non-renewable mineral resource could be considered a con- straint on other use of the property, areas of diatomite deposits are designated on plate la as item 7. More information on these deposits is available in a recent article by Clark (1978). California, for many years, has been the largest pro- ducer of diatomite, supplying approximately 60% of the total production in the United States. Western Santa Barbara County contains the most extensive known deposits of high-quality marine diatomite in the world. Diatomite and bituminous diatomaceous shale have been mined in the Casmalia Hills (Guadalupe Quadrangle) at the Airox Corporation, NTU, and Waldorf Mines. These deposits were mined both for diatomite products and f6r petroleum by-products. Extensive building on top of a valuable, or potentially valuable, non- renewable mineral resource can effectively eliminate that resource as a mineable commodity. Such a land use policy can lead to future shortages, higher prices, and potential elimination of the comwdity. In this respect, the potentially mineable diatomite resources are designated on plate la as item 7 as a geologic element significant to planning. 35 In addition to the constraining aspects (loss of mineral resources), some of the diatomaceous deposits of this region can be considered a positive factor in the siting of certain facilities. The location of the Casmalia Class I disposal site on the adjoining Casmalia quadrangle is such a case. Here, the absorptive, filtering and impermeable nature of a diatomaceous porcelaneous mudstone are positive factors in the selection of a site as a stiorage dump for highly toxic waste materials. The nature of the Todos Santos Claystone member of the Sisquoc Formation as described and shown on the map of Woodring and Bramlette (1950), in general, shows these absorption, filtering, and impermeable character- istics. This deposit extends onto the Guadalupe Quadrangle in the south central portion adjacent to the purer diatomite shown as item 7 on plate la. To avoid confusion, the claystone unit has not been separately desig- nated on the hazard/constraint maps but is well illustrated at the same scale on Plate I of Woodring and Bramlette (1950). 4. Unique Geologic Features Many unique geologic features can be found in the area of the Point Sal and Guadalupe 7.51 Quadrangles. A few of these features have been subjectively selected as important enough to be considered in regional planning (plates la and 2a, items 8a-j). The features depicted are con- sidered by the authors of this report to represent a unique geologic feature of significant scientific and/or educational value. All of the features selected have been described in the literature and are 36 used by teachers, students, and professional geologists for educational field trips. Only geologic criteria were used in selection though some of the areas also contain botanical, archeological, zoological, recrea- tional, and scenic values. Several of the features designated are unique fossil occurrences, but not all fossil sites have been designated as unique. In fact, only a few of the more than 46 fossil localities described by Woodring and Bramlette (1950) for the subject quadrangles were classified in this report as unique geologic features. Criteria such as: species diversity, quality of preservation, accessibility for study, species type localities, number of literature citings, uniqueness of the fossil assemblage, and importance to stratigraphic definitions were subjectively weighed in choosing the fossil localities that have been put on plates la and 2a. The value of these localities is hard to estimate, but would include the fact that they constitute the principal basis for regional correlation and age dating of stratigraphic units within the Santa Maria basin, and to a lesser extent, the world. They have value as natural educational exhibits and sources of material for paleontological research. Section 6222, Part 1, Title 14, of the California Penal Code, which is commonly thought to protect fossil localities, though possibly applicable to these sites does not appear to protect them adequately from destruction. 37 Individual features occuring in the Guadalupe and Point Sal Quad- rangles are described below: Plate la Plate 2a Number Quadran2le. Significance of Feature 8a Guadalupe The area, shown on Plate la, encompasses three fossil assemblage sites as described by Woodring and Bramlette (1950). All three contain abundant mollusc specimens and all three have been assign- ed permanent United States Geological Survey locality numbers (14934, 14896, and 14608) registered in the Cenozoic Invertebrate Register. Locality 14609 appears to be the type locality for the gastropod species Bittium casmaliense (Bartsach, 19111. About 40 molluscan species were identified from this area by W.P. Woodring and Bramlette, 1950). 8b Guadalupe Area Bb, as shown on Plate la, constitutes a well known and described complete section of the Plio- cene Foxen Mudstone (Woodring and Bramlette, 1950). The section contains several fossiliferous strata and has a total thickness of 175 meters. one of the fossiliferous beds has been assigned a permanent 38 U.S. Geological Survey locality number (14877) re- gistered in the Cenozoic Invertebrate Register. 27 species of benthic Foraminifera and 5 species of molluscs have been identified as occurring in this section by Woodring and Bramlette (1950). 8c Guadalupe Area 8c, as shown on Plate la, is a rare fresh water gastropod fossil locality in the Plio-Pleistocene Paso Robles Formation. The locality has been des- cribed by Woodring and Bramlette (1950) and has been assigned a permanent U.S. Geological Survey locality number (14887) registered in the Cenozoic Inverte- brate Register. 8d Guadalupe Area 8d, as shown on Plate la, is the mine dump of the abandoned Waldorf asphalt mine. The mine start- ed operation before the turn of the century and is shown on a map by Eldridge (1901). The site is a very important fossil locality in the Pliocene Foxen Mudstone and has been extensively collected and de- scribed in the literature by Dall (1903), Arnold (1907), Bartsch (1911), Carson (1926), and Woodring and Bramlette (1950). In the latte@ report, the lo- cality is described in the following manner: "The dump is an important locality, not only because of the large number of well preserved fossils, the ex- ceptional preservation of which is due principally to 39 impregnation with asphalt, but also because it is the type locality of five forms: Nassa waldorfensis, Ocinebra micheli var. waldorfensis, Drillia waldor- fensiso, Leda orcutti, and Venericardia californica. More than three quarters of the known Foxen fauna is recorded only from this locality". The site has been assigned two permanent U.S. Geological Survey numbers (4473, 14879) registered in the Cenozoic invertebrate Register. 8e Guadalupe Area 8e, as shown on plate la, is the site of the NTU Co. oil mine. The mine operated from 1923 to 1928. Based on tonnage mined and average grade of the de- posit as estimated by Williams and Holmes (1945) and Gore (1923) it can be estimated that the NTU mine produced 27,000 bbls of oil. Williams and Holmes (1945) estimate that 100,000 bbls of oil are left in the part of the Sisquoc Formation actually visible in the NTU quarry. Fossils from the NTU mine site have been collected and described by Woodring and Bramlette (1950). They state: wonly two unusual localities", (within the basin facies of the Sisquoc Formation) *the NTU mine in the Casmalia Hills and the dump of the old Pennsylvania asphalt mine in the Orcutt field yielded more than 10 species" of molluscs. This site (the NTU mine) has yielded 16 40 species of molluscs and has been assigned a U.S. Geo- logical Survey locality number (14878) registered in the Cenozoic Invertebrate Register. 8f Point Sal Area 8f, as shown on plate 2a, is the largest re- gion designated in this category. The reasons for its scientific and educational significance are multiple. The sea cliff and canyon exposures in- clude outcrops representing more than 100 million years of Santa Maria Basin stratigraphy. The ex- posures include: Franciscan Formation, Knoxville Formation, Lospe Formation, Point Sal Formation, Monterey Formation, Sisquoc Formation, Older and Modern dune sands (of Woodring and Bramlette, 1950), and at least three late Pleistocene marine terraces. These units are selectively complexly folded and faulted and contain classic exposures of a multitude of geologic structures that students and profession- als of geology and natural history seldom see outside of the textbook. The section includes well exposed examples of normal and reverse faults, fault gouge, slickensides, drag folding, asphalt seeps, angular unconformities, disconformities, nonconforruties, overturned bedding, cross bedding, graded bedding, fossil localities, anticlines, synclines, landslides, a well documented ophiolite sequence, gypsum and dia- 41 tomite deposits, and even minor sulfide mineraliza- tion. The section exposed along the sea cliff and Mussel Rock Creek Canyon constitutes a unique outdoor classroom for structural, petroleum, and general geo- logy students. This area has been used for educational field trips by organizations as diverse as the Geolo- gical Society of America, Mobil Oil Corporation, and Cal- ifornia Polytechnic State University. A unique section of exhumed marine terrace topography is exposed in the lowest 0.5 km of Mussel Rock Creek Canyon. At least three Late Pleistocene terraces are well ex- posed in an exhumed topographic setting caused by erosion of modern and older dune sand. The lowest wave cut terraces contain trace fossils of burrow- ing pelecypods. Carbon-14 analysis of mollusc shells collected from beach deposits at an an- proximate elevation of 10 m, lying above the low- est terrace, have yielded a preliminary age determi- nation of 25,460+ 470 years before present. (Kenneth Lajoie, personal communication, 1980). This strongly suggests an Oxygen-18 Stage 3 correlation for the youngest terrace, an unusual occurence for the Calif- ornia Coast.. At a locality approximately 100 m NW of the mouth of Mussel Rock Creek and an elevation of 30 meters an aboriginal kitchen midden site was discovered containing abundant Mytilus californianus These shells are being Carbon-14 dated and probably are derived from the Chunash Indian village of Kasriali. 42 ACKNOWLEDGF14ENTS The authors wish to acknowledge the help of Robert Strand of the California Energy Commission, Richard McCarthy of the California Coastal Commission, Roger Sherburne, Richard Stewart, Carl Hauge, and Dave Beeby of California Division of Mines and Geology (CDMG) for their critical review of this manuscript. George Saucedo of CDMG assisted in office studies and JAm s Moreno assisted Kilbourne in field qhecking the map portions of the report. The manuscript was typed by Delores Patterson of the CDMG San Francisco Office and Irene Turner of the CDMG Sacramento office. 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Worts, G.F., Jr., 1951, Geology and groundwater resources of the Santa Maria Valley area, California: U.S. Geological Survey Water Supply Paper 1000, 169 p., pi. 1, map scale 1:62,500. 48 ISTA f OF CALIFO"IA ws@fs @Kl CAL Wo"m W."m or 0".r$ AW $mod, or, fsfw.s votatatows, A-tw or @m..Tmw MAGNITUDE .::::.11?0 Tpo 34?9 (D .& ... 5.0 TO 5.9 (D ..... 6.0 TO 6.9 (D ..... 7.0 TO 7.9 + 36-000 DIGIT/LETTER ..... MAXIMUM REPORTED INTENSITY, 9..... ROSSI-FOREL e 5 ..... MODIFIED MtRCALLI 0. (D &' 0 0 00 0 %D + 35.000 + e 00 S 'p too 0 0 + 34-000 a 0 a w w 40 wm EPICENTER MAP OF E ARTHOUAKES (M>-3) WITHIN 120KM OF THE CENTER OF THE USGS GUADALUPE 71/2'QUADRANGLE (1900-1975) I I I @ 3 6668 14109 6265