APPENDIX B ONSHORE-OFFSHORE GEOLOGIC MAP THE SHORELINE FAULT ZONE STUDY AREA, SAN LUIS OBISPO COUNTY Shoreline Fault Zone Report, Appendix B Geology Page B-1 of 112 TABLE OF CONTENTS 1. INTRODUCTION ..................................................................................................................... 5 1.1 Purpose and Objectives........................................................................................................ 5 1.2 Previous Investigations ........................................................................................................ 5 1.3 New Base Map..................................................................................................................... 6 1.4 New Data Sources................................................................................................................ 6 2. METHODOLOGY .................................................................................................................... 7 2.1 Onshore Mapping................................................................................................................. 7 2.2 Offshore Mapping................................................................................................................ 7 3. GEOMORPHOLOGY ............................................................................................................. 10 3.1 San Luis Range .................................................................................................................. 10 3.2 Continental Shelf ............................................................................................................... 11 4. STRATIGRAPHY ................................................................................................................... 14 4.1 Mesozoic Formations......................................................................................................... 14 4.2 Tertiary Stratigraphy.......................................................................................................... 15 4.3 Quaternary Stratigraphy..................................................................................................... 19 5. STRUCTURE .......................................................................................................................... 20 5.1 Tectonic History................................................................................................................. 20 5.2 Basement Structures........................................................................................................... 22 5.3 Tertiary Structures ............................................................................................................. 22 5.3.1 Deformation of the Tertiary/basement contact ........................................................... 22 5.3.2 Deformation within the Obispo Formation................................................................. 22 5.3.4 Deformation within the Pismo Formation .................................................................. 24 5.4 Quaternary Structures ......................................................................................................... 25 5.4.1 Hosgri fault zone......................................................................................................... 25 5.4.2 N40W fault.................................................................................................................. 27 5.4.3 Shoreline fault zone .................................................................................................... 28 5.4.4 San Luis Bay fault zone .............................................................................................. 39 6. CONCLUSIONS................................................................................................................... 43 7. REFERENCES ..................................................................................................................... 45 LIST OF TABLES Table B-1 Drop core samples from the LTSP Table B-2 Diver samples from the LTSP Table B-3 Diver samples from the 2010 campaign Table B-4 Characteristics of the N40W fault Table B-5 Characteristics of the North segment Shoreline fault Table B-6 Characteristics of the Central segment Shoreline fault Table B-7 Characteristics of the South segment Shoreline fault Shoreline Fault Zone Report, Appendix B Geology Page B-2 of 112 LIST OF FIGURES Figure B-1-1 Areas of previous geologic mapping Figure B-1-2 Comparison of (a) USGS topography with (b) the new LiDAR topography at San Luis Hill Figure B-1-3 Comparison of (a) LTSP bathymetry with (b) the new MBES bathymetry at Pecho Rock Figure B-2-1 Offshore samples obtained during the LTSP and in 2010 for this study Figure B-2-2 Comparison of (a) LTSP geology map with (b) the new geologic map near Olson Hill Figure B-3-1 Geomorphic regions in the Shoreline fault zone study area Figure B-3-2 Characteristics of the Islay and Santa Rosa Reef shelves Figure B-3-3 Structure contours on top of bedrock on the Islay and Santa Rosa Reef shelves Figure B-3-4 Channel profiles of the thalwegs of Islay and Pecho Creeks Figure B-3-5 Migration of sand sheet along the Central segment of the Shoreline fault zone between the 2009 and 2010 MBES bathymetric surveys northwest of Olson Hill Figure B-3-6 Faults and paleostrandlines in the Shoreline fault zone study area Figure B-4-1 Simplified geologic map of the Shoreline fault zone study area with seismicity Figure B-4-2 Stratigraphy of the coastline exposures and offshore area adjacent to DCPP Figure B-4-3 Faults from geologic map overlain with composite magnetic-field anomalies from marine and helicopter surveys Figure B-4-4 Generalized area of Franciscan mélange offshore compared to magnetic-field anomalies Figure B-5-1 Comparison of (a) the geology with (b) the magnetic-field anomalies in the DCPP area Figure B-5-2 Comparison of (a) the Crowbar fault interpreted from the LTSP with (b) offshore faults in the Pismo Formation interpreted from this study Figure B-5-3 Comap seismic-reflection lines CM-21 and CM-23 across the Hosgri fault zone and north ends of the North segment Shoreline and N40W faults Figure B-5-4 Comparison of (a) MBES bathymetric image with (b) the interpreted geology and (c) paleostrandlines across the N40W fault Figure B-5-5 Comparison of (a) MBES bathymetry with (b) interpreted geology and (c) paleostrandlines across the Central segment (C-1) of the Shoreline fault zone west of DCPP Figure B-5-6 Comparison of (a) MBES bathymetry with (b) interpreted geology and (c) paleostrandlines across the Central segment (C-2) of the Shoreline fault zone southwest of the DCPP entrance Figure B-5-7 Comparison of (a) MBES bathymetry with (b) interpreted geology and (c) paleostrandlines across the Central segment (C-2) of the Shoreline fault zone west of Olson Hill Shoreline Fault Zone Report, Appendix B Geology Page B-3 of 112 Figure B-5-8 Comparison of (a) MBES bathymetry with (b) interpreted geology and (c) paleostrandlines across the Central segment (C-3) of the Shoreline fault zone west of Rattlesnake Creek Figure B-5-9 Comparison of (a) MBES bathymetry with (b) interpreted geology and (c) paleostrandlines across the South segment of the Shoreline fault zone southwest of Point San Luis Figure B-5-10 Apparent offset of Cretaceous sandstone beds across the Rattlesnake fault, San Luis Bay fault zone LIST OF PLATES Plate B-1A North section geologic map, Morro Bay to Point Buchon Plate B-1B Central section geologic map, Point Buchon to Double Rock Plate B-1C South section geologic map, Double Rock to San Luis Hill Plate B-1D Southeast section geologic map, Point San Luis to Pismo Beach LIST OF ATTACHMENTS Attachment 1 2010 Dive Sample Descriptions Shoreline Fault Zone Report, Appendix B Geology Page B-4 of 112 1. INTRODUCTION This appendix presents a comprehensive geologic map from a compilation of existing and new geologic mapping and geophysical data both onshore and offshore in the Shoreline fault zone study area. The study area extends from the western slope of the Irish Hills on the east to the edge of the continental shelf at the Hosgri fault zone on the west, and from Estero Bay on the north to Pismo Beach on the south (Figure B-1-1). The geologic map is presented in four plates at 1:12,000 scale (Plates B-1A to B-1D). 1.1 Purpose and Objectives The purpose of creating an onshore-offshore geologic map of the study area is to place the Shoreline fault zone in its geologic context. The objectives of the mapping include: 1. Complete a geologic map of the study area using previous and new field mapping plus the newly acquired MBES and LiDAR images, dive samples, seismic-reflection profiles, and high-resolution helicopter magnetic field data; 2. Characterize the length, segmentation, style of faulting, and slip rate of the Shoreline fault zone; 3. Accurately locate the fault trace where it lies offshore of DCPP; 4. Assess the relation of the mapped traces of the Shoreline fault zone to the seismicity lineament that originally defined the Shoreline fault; and 5. Evaluate the evidence, if any, of late Quaternary displacements on the fault. 1.2 Previous Investigations Existing onshore geologic maps within the DCPP site vicinity are shown on Figure B-1-1. Mapping of the Irish Hills (i.e., Point San Luis and Morro Bay topographic quadrangles) was completed at 1:24,000-scale by Hall (1973a) and later incorporated into a regional compilation by Hall et al. (1979) with minor revisions at 1:48,000