David C. Twichell VeeAnn A. Cross 2003 1.0 vector digital data Open-File Report 02-478 Woods Hole Field Center, Woods Hole, MA U.S. Geological Survey, Coastal and Marine Geology https://doi.org/10.3133/ofr02478 VeeAnn A. Cross David C. Twichell 2003 1.0 Open-File Report 02-478 Woods Hole Field Center, Woods Hole, MA U.S. Geological Survey, Coastal and Marine Geology Team https://doi.org/10.3133/ofr02478 Lake Mead is a large interstate reservoir located in the Mojave Desert of southeastern Nevada and northwestern Arizona. It was impounded in 1935 by the construction of Hoover Dam and is one of a series of multi-purpose reservoirs on the Colorado River. The lake extends 183 km from the mouth of the Grand Canyon to Black Canyon, the site of Hoover Dam, and provides water for residential, commercial, industrial, recreational, and other non-agricultural users in communities across the southwestern United States. Extensive research has been conducted on Lake Mead, but a majority of the studies have involved determining levels of anthropogenic contaminants such as synthetic organic compounds, heavy metals and dissolved ions, furans/dioxins, and nutrient loading in lake water, sediment, and biota (Preissler, et al., 1998; Bevans et al, 1996; Bevans et al., 1998; Covay and Leiker, 1998; LaBounty and Horn, 1997; Paulson, 1981). By contrast, little work has focused on the sediments in the lake and the processes of deposition (Gould, 1951). To address these questions, sidescan-sonar imagery and high-resolution seismic-reflection profiles were collected throughout Lake Mead by the USGS in cooperation with researchers from University of Nevada Las Vegas (UNLV). These data allow a detailed mapping of the surficial geology and the distribution and thickness of sediment that has accumulated in the lake since the completion of Hoover Dam. Results indicate that the accumulation of post-impoundment sediment is primarily restricted to former river and stream beds that are now submerged below the lake while the margins of the lake appear to be devoid of post-impoundment sediment. The sediment cover along the original Colorado River bed is continuous and is typically greater than 10 m thick through much of its length. Sediment thickness in some areas exceeds 35 m while the smaller tributary valleys typically are filled with less than 4 m of sediment. Away from the river beds that are now covered with post-impoundment sediment, pre-impoundment alluvial deposits and rock outcrops are still exposed on the lake floor. This ArcView shapefile is used to enable correlation between the seismic-reflection profiles and the sidescan-sonar imagery, geologic interpretation, and other features represented on the lake floor. These data were collected as part of USGS field activity 2001-007-FA. Additional information about that field activity is available from https://cmgds.marine.usgs.gov/services/activity.php?fan=2001-007-FA . 20010401 20010416 ground condition Complete None planned -114.756065 -114.024584 36.484177 36.014389 USGS Metadata Identifier USGS:61ccd6a5-2ba3-483d-9b7d-197a6039b20c None seismic shotpoint navigation subbottom seismic reflection chirp SIS-1000 U.S. Geological Survey USGS Coastal and Marine Geology Program CMGP Woods Hole Field Center Open-File Report OFR02-478 USGS Thesaurus geospatial datasets seismic reflection methods marine geophysics navigational data ISO 19115 Topic Category geoscientificInformation inlandWaters None Nevada Lake Mead reservoir Hoover Dam Boulder Basin Virgin Basin Gregg Basin Overton Arm Mojave Desert No access constraints. Please see 'Distribution Information' for details. These data are marked with a Creative Commons CC0 1.0 Universal License. These data are in the public domain and do not have any use constraints. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. The U.S. Geological Survey must be referenced as the originator of the dataset in any future products or research derived from these data. David C. Twichell U.S. Geological Survey Oceanographer mailing and physical address

384 Woods Hole Rd.

Woods Hole MA 02543-1598 508-548-8700 x2266 508-457-2310 dtwichell@usgs.gov Microsoft Windows 2000 Version 5.0 (Build 2195) Service Pack 3; ESRI ArcCatalog 8.2.0.700 H.E. Bevans S.L. Goodbred J.F. Miesner S.A. Watkins T.S. Gross N.D. Denslow T. Choeb 1996 Water-Resources Investigations 96-4266 Reston, VA U.S.Geological Survey Water Resources H.E. Bevans M.S. Lico S.J. Lawrence 1998 Circular 1170 Reston, VA U.S. Geological Survey https://doi.org/10.3133/cir1170 K.J. Couvay T.J. Leiker 1998 Open-File Report 98-633 Reston, VA U.S. Geological Survey https://doi.org/10.3133/ofr98633 H.R. Gould 1951 SEPM Society for Sedimentary Geology Special Publication No. 2 McLean, VA SEPM Society for Sedimentary Geology https://doi.org/10.2110/pec.51.02.0034 J.F. LaBounty M.J. Horn 1997 Journal of Lake and Reservoir Management v. 13, issue 2 London, England Journal of Lake and Reservoir Management https://doi.org/10.1080/07438149709354301 L.J. Paulson 1981 Technical Report #8 Department of Biological Sciences, University of Nevada, Las Vegas, Nevada Lake Mead Limnological Research Center These data have been checked to remove obviously erroneous data points. These data represent shotpoint navigation for all the seismic lines collected on this cruise. The navigation was collected with a P-CODE GPS receiver with an assumed accuracy of approximately 10m. Additional error is introduced by undertainty as to the positional relationship between the acquisition system and the navigation antenna. Overall positional accuracy assumed to be 20 meters. 20 The navigation was collected with a P-CODE GPS receiver with an assumed accuracy of approximately 10m. Additional error is introduced by undertainty as to the positional relationship between the acquisition system and the navigation antenna. Overall positional accuracy assumed to be 20 meters. This particular seismic data was acquired with an SIS-1000 chirp subbottom system with the digital data stored on a Triton-QMIPS datalogger. Navigation is updated approximately every 10 seconds and sent to this data logging system. Once the seismic SEG-Y data is separated from the raw data files, the unique navigation points and the shotpoints associated with them are pulled from the header of these seg-y data files. These navigation points reflect the best known position of the acquisition system. In other words, the layback of the instrument is taken into account for the positional fix. *The process date was added as a required element when the metadata was updated in 2026. The process date is an assumption based on the process step itself. 2001 The shot point navigation for each line of seismic data was combined into a single file and then resampled using DigiRule's GeoCad program to a shot interval of 100. The beginning and ending shot of each line was maintained. *The process date was added as a required element when the metadata was updated in 2026. The process date is an assumption based on the process step itself. 2002 These points were then imported into ArcView and saved as a shapefile. *The process date was added as a required element when the metadata was updated in 2026. The process date is an assumption based on the process step itself. 2002 Since the original navigation was stored in the SEG-Y header in UTM, zone 11, NAD 83 meters, the file was then reprojected to the Geographic Coordinate system using ArcToolbox in ArcGIS 8.1. *The process date was added as a required element when the metadata was updated in 2026. The process date is an assumption based on the process step itself. 2002 This metadata file was updated as part of metadata maintenance when added to the web accessible folder. Edits were performed on the original text version of the metadata, then converted to XML. These edits included: Fixed all errors flagged by MP. These included (but are not limited to) adding required elements such as publication place when publisher is provided; added process dates. Additionally, added some DOI online links when possible; added supplemental information with link to the field activity; added USGS Thesaurus and ISO 19115 Topic Category thesauri and appropriate terms in each; renamed “General” thesauri to “None” thesauri; updated the use and access constraints to approved statements; updated the distribution liability to a current approved statement; updated metadata email to a generic email in the event the person leaves the USGS (20260521) 20260521 U.S. Geological Survey VeeAnn A. Cross Marine Geologist mailing and physical address

384 Woods Hole Rd.

Woods Hole MA 02543-1598 USA (508) 548-8700 x2251 (508) 457-2310 vatnipp@usgs.gov Vector Entity point 6759 0.0002 0.0002 Decimal degrees North American Datum of 1983 Geodetic Reference System 80 6378137.000000 298.257222 lm01_100sht.dbf ArcView shapefile attribute table ESRI FID Internal feature number. ESRI Sequential unique whole numbers that are automatically generated. Shape Feature geometry. ESRI Coordinates defining the features. LINENUM Line number assigned to the seismic line along which the shotpoint navigation point falls. Data processor character set SHOT The seismic shot number corresponding to that point. Software computed. 1 17143 EASTING The UTM easting position of the shot point. Software generated. 702048 767566 NORTHING The UTM northing position of the shot point. Software computed. 3989078 4040949 David C. Twichell U.S. Geological Survey Oceanographer mailing and physical address

384 Woods Hole Rd.

Woods Hole MA 02543-1598 508-548-8700 x2266 508-457-2310 dtwichell@usgs.gov Downloadable Data 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 for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. shapefile 0.494 These data were released on DVD that is currently not available online. Not documented with the original metadata. None 20260602 VeeAnn A. Cross U.S. Geological Survey Marine Geologist mailing and physical address

384 Woods Hole Rd.

Woods Hole MA 02543-1598 508-548-8700 x2251 508-457-2310 whsc_data_contact@usgs.gov The metadata contact email address is a generic address in the event the contact person is no longer with the USGS. FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998