Antoinette G. Papesh Maureen L. Walton James E. Conrad Daniel S. Brothers Jared W. Kluesner Mary L. McGann 20230821 polygon shapefile data release DOI:10.5066/P9IIWTYL Pacific Coastal and Marine Science Center, Santa Cruz, CA U.S. Geological Survey https://doi.org/10.5066/P9IIWTYL https://www.sciencebase.gov/catalog/item/5ef12a2682ced62aaae18f67 Antoinette G. Papesh Maureen L. Walton James E. Conrad Daniel S. Brothers Jared W. Kluesner Mary L. McGann 2023 data release DOI:10.5066/P9IIWTYL Pacific Coastal and Marine Science Center, Santa Cruz, CA U.S. Geological Survey https://doi.org/10.5066/P9IIWTYL Landslide debris aprons have been mapped offshore of Southern California. Polygons were mapped from visual interpretation of high-resolution multibeam echosounder data (MBES), single-beam echosounder data, and seismic reflection data. These data were compiled as a part of a USGS effort to understand the geologic processes of mass wasting offshore of Southern California. They are intended to provide baseline knowledge of the geology, geomorphology, and distribution of landslides debris aprons offshore of Southern California, for use by scientists, managers, and the general public. These data can be used with geographic information systems (GIS) software for research purposes. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in Esri format, this metadata file may include some Esri-specific terminology. 1998 20210730 ground condition Complete None planned -120.913005 -117.313146 34.517488 32.465078 ISO 19115 Topic Category geoscientificInformation oceans Data Categories for Marine Planning Distributions USGS Thesaurus scientific interpretation geospatial datasets earth characteristics sea-floor characteristics marine geophysics marine geology landslides hazards geologic processes oceanic lithosphere Marine Realms Information Bank (MRIB) keywords natural agents of coastal change geology geophysics geological features hazards and disasters earthquake effects geologic mapping oceanographic observations None U.S. Geological Survey USGS Coastal and Marine Hazards and Resources Program CMHRP Pacific Coastal and Marine Science Center PCMSC USGS Metadata Identifier USGS:5ef12a2682ced62aaae18f67 Geographic Names Information System (GNIS) United States of America State of California Pacific Ocean None USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data. U.S. Geological Survey, Pacific Coastal and Marine Science Center PCMSC Science Data Coordinator mailing and physical

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Santa Cruz CA 95060 831-427-4747 pcmsc_data@usgs.gov debrisaprons_offshore_socal_2023_thumb.png Southern California location map with bathymetry and mapped debris aprons PNG Mac Pro, Late 2013, with macOS High Sierra, version 10.13.6 running Parallels Virtual Machine; ESRI ArcGIS 10.7. No formal attribute accuracy tests were conducted. No formal logical accuracy tests were conducted. Dataset is considered complete for the information presented, as described in the abstract. These data and associated attributes have been created from several bathymetric datasets. Landslide debris apron mapping was cross-checked where more than one bathymetric dataset spanned a suspected landslide debris apron. The accuracy of debris apron mapping correlates to the highest resolution dataset that spans a particular debris apron. Peter Dartnell Neal W. Driscoll Daniel S. Brothers James E. Conrad Jared Kluesner Graham Kent Brian D. Andrews 2015 Raster Digital Data Set Scientific Investigations Map DOI:10.3133/sim3324 Reston, VA U.S. Geological Survey https://doi.org/10.3133/sim3324 Digital Resource 1998 2014 ground condition Dartnell and others, 2015 High resolution multibeam bathymetry was used as a base layer to begin drawing polygons for landslide interpretation. Peter Dartnell Emily C. Roland Nicole A. Raineault Christopher M. Castillo James E. Conrad Renato Kane Daniel S. Brothers Jared W. Kluesner Maureen A. L. Walton 2021 Raster Digital Data Set Scientific Investigations Map DOI:10.3133/sim3473 Reston, VA U.S. Geological Survey https://doi.org/10.3133/sim3473 Digital resource 1998 2018 ground condition Dartnell and others, 2021 High resolution multibeam bathymetry was used as a base layer to begin drawing polygons for landslide interpretation. This is a compilation of publicly available multibeam bathymetry data published at various resolutions ranging from 2-30 meters. Data sources used are shown on Figure 1 of the report and links to the data are provided therein. Seafloor Mapping Lab of California State University Monterey Bay 2018 Raster Digital Data Sets Seaside, CA California State University, Monterey Bay http://seafloor.otterlabs.org/SFMLwebDATA.htm Digital resource 2000 2018 ground condition Seafloor Mapping Lab, 2018 High resolution multibeam bathymetry was used as a base layer to begin drawing polygons for landslide interpretation. High resolution multibeam bathymetry data at resolutions ranging from 2 – 10 meters from survey datasets H11875, H11876, H11877, H11878, H11879, H11880, H11881, H11882, H11883, H11891, H11950, H11951, H11952, H11953, and the 2014 Southern California Data Gap Project (Dana Point, San Onofre Blocks 01-03, La Jolla, Mission Beach, Point Loma North, Point Loma South, and Imperial Beach) were used. MBARI Seafloor Mapping Team 2001 Raster Digital Data Set online MBARI https://www3.mbari.org/data/mapping/Santa_Barbara_Basin/ Digital resource 1998 2001 ground condition MBARI Seafloor Mapping Team, 2001 High resolution multibeam bathymetry was used as a base layer to begin drawing polygons for landslide interpretation. This is 20-meter resolution bathymetry data. NOAA 2012 Raster Digital Data Sets online NOAA https://doi.org/10.7289/V5V985ZM Digital resource 19990101 Present published 2013-07-08 National Geophysical Data Center, 2012 The NCEI 3-arc-second elevation grid (approximately 90-meter resolution) was used as a base layer to begin drawing polygons for landslide interpretation where no high resolution multibeam bathymetry data (listed above) were available. Ray W. Sliter James E. Conrad Holly F. Ryan Peter J. Triezenberg 2017 seismic-reflection data in SEG-Y format Data Release DOI:10.5066/F7QN64W8 Pacific Coastal and Marine Science Center, Santa Cruz, CA U.S. Geological Survey https://doi.org/10.5066/F7QN64W8 https://cmgds.marine.usgs.gov/data-releases/datarelease/10.5066-F7QN64W8/ Digital resource 20100601 20100612 ground condition Sliter and others, 2017a Seismic reflection profiles were used to map extent of debris apron for the Del Mar slide. Ray W. Sliter James E. Conrad Holly F. Ryan Peter J. Triezenberg 2017 seismic-reflection data in SEG-Y format Data Release DOI:10.5066/F7SF2TCV Pacific Coastal and Marine Science Center, Santa Cruz, CA U.S. Geological Survey https://doi.org/10.5066/F7SF2TCV https://cmgds.marine.usgs.gov/data-releases/datarelease/10.5066-F7SF2TCV/ Digital resource 20110608 20110622 ground condition Sliter and others, 2017b Seismic reflection profiles were used to map extent of debris apron for the San Gabriel Slide Complex. A compilation of existing bathymetry data was used as a base layer to map landslide features. Data from listed sources was downsampled in ESRI ArcMap and merged into a single 30-m grid to create the base layer. In some cases, the source swath data was higher resolution than the 30-m compilation and was used to map landslide features. A list of source swath data is detailed in the Source Used Citations. Where high (<30 m) resolution data was unavailable, the 90-m resolution NOAA Coastal Relief Model was used as the base layer. Using this base layer, landslides, headwall scarps, and areas of mass-wasting were mapped. Mapped landslide bodies were divided into evacuation zones and debris aprons based on negative (i.e., evacuation zones) or positive (i.e., debris aprons) seafloor relief associated with the landslide masses. Dartnell and others, 2015 Dartnell and others, 2021 Seafloor Mapping lab, 2018 MBARI Seafloor Mapping Team, 2001 NOAA National Geophysical Data Center, 2012 Sliter and others, 2017a Sliter and others, 2017b 20230202 Vector GT-polygon composed of chains 63 0.0001 0.0001 Decimal degrees D_WGS_1984 WGS_1984 6378137.0 298.257223563 debrisaprons_offshore_socal_2023 polygons representing mapped landslide debris aprons U.S. Geological Survey FID internal feature number Esri automatically generated sequential unique whole number identifier Shape feature geometry Esri feature type name_id the name of the debris apron U.S. Geological Survey and California Geological Survey The names of the landslide debris aprons are identical to the names of the landslide feature in which the debris apron belongs (see landslides_offshore_socal_2023.shp, available elsewhere in this data release). We define prefixes as follows: CB is Catalina Basin; CI is Catalina Island; GSC is Gulf of Santa Catalina; PA is Point Arguello; SBB is Santa Barbara Basin; SClB is San Clemente Basin; SCB is Santa Cruz Basin; SDT is San Diego Trough; SG is San Gabriel; SNB is San Nicolas Basin; SPB is San Pedro Basin. area_m2 Area of debris apron in square meters Esri 19963 196388611 square meters 1 area_err Estimated uncertainty of debris apron area from data resolution and user interpretation, values in square meters. GIS-calculated area was approximated as a circle geometry with radius uncertainty of plus or minus 50 meters and plus or minus 20 meters for areas greater and less than 100,000 square meters, respectively. These values are based on 2 pixels of the likely resolution of bathymetric data used for mapping (25-meter and 10-meter resolutions). The calculated error is the standard deviation of the maximum, minimum, and picked geometries. U.S. Geological Survey 10043 2481440 square meters 1 Polygon shapefile containing outlines and attributes of landslide debris aprons offshore of Southern California U.S. Geological Survey U.S. Geological Survey - ScienceBase Mailing and Physical

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Denver CO 80225 1-888-275-8747 sciencebase@usgs.gov debrisaprons_offshore_socal_2023.zip contains the shapefile and associated files, and is accompanied by a browse image and CSDGM FGDC-compliant metadata. Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. Shapefile ArcGIS 10.7 polygon shapefile Zip file contains the interpreted polygons shapefiles and the associated metadata Winzip, 7-zip, or Winrar are free software that will open .zip files. 0.04 https://www.sciencebase.gov/catalog/file/get/5ef129c982ced62aaae18f67 https://www.sciencebase.gov/catalog/item/5ef129c982ced62aaae18f67 https://doi.org/10.5066/P9IIWTYL Data can be downloaded using the Network_Resource_Name links. The first link is a direct link to download the zipped file of data and metadata. The second link points to a landing page with metadata and data. The third link points to the landing page for the entire data release. None. These data can be viewed with GIS software. 20230821 U.S. Geological Survey, Pacific Coastal and Marine Science Center PCMSC Science Data Coordinator mailing and physical

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Santa Cruz CA 95060 831-427-4747 pcmsc_data@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998