|Range of values|
|alluvial||Areas where pre-impoundment alluvial fan deposits are exposed on the lake floor. These deposits show on the sidescan imagery as moderate backscatter areas that are interrupted by thin sinuous bands of low backscatter (dark tones) shaped in a distributary pattern.|
|rock||Areas where rock is exposed on the lake floor. Rock exposures show as either uniform high backscatter (light tones) or alternating bands of high and moderate backscatter (light and moderate tones) on the sidescan imagery.|
|thick sed||Areas of the lake floor covered by post-impoundment sediment that is more than 1 m thick. These areas show on the sidescan imagery as low backscatter (dark tones) throughout the lake with the exception of parts of Gregg Basin and the area at the mouth of Las Vegas Wash which are sandy and have a moderate backscatter surface. The thickness of the sediment being greater than 1 m is determined from the seismic-reflection profiles.|
|thin sed||Areas of the lake floor covered by post-impoundment sediment that is less than 1 m thick. These areas show on the sidescan imagery as low backscatter (dark tones). The sediment thickness for much of these areas was below the resolution of the seismic-reflection system used, and in these areas the presence of post-impoundment sediment is based on the low-backscatter signature on the sidescan imagery alone.|
|Boulder Basin||The area of the lake to the west of Boulder Canyon.|
|Virgin Basin||The central basin of Lake Mead. Starts at (includes) Boulder Canyon in the west, and extends to the east until it runs into Temple Basin. The northern boundary is marked by the Overton Arm section of the lake.|
|Overton Arm||The northernmost portion of Lake Mead, where the Muddy River and Virgin River enter the lake. The southern boundary is marked by the Virgin Basin.|
|Temple Basin||Western boundary is marked by Virgin Basin. This area includes Temple Basin as well as the Virgin Canyon area to the east.|
|Gregg Basin||The easternmost portion of Lake Mead. The western boundary is at the entrance to Virgin Canyon, and the eastern boundary extends to the limits of the survey. The Colorado River enters Lake Mead to the east.|
|Range of values|
|Range of values|
This shapefile presents an interpretation of the surficial geology of the floor of Lake Mead based on sidescan-sonar imagery, bathymetry, seismic-reflection data, and geological maps of the areas surrounding the lake.
Are there legal restrictions on access or use of the data?
Use_Constraints:The interpretation was completed at map scales less than 1:10,000, and is not intended for use smaller map scales. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information.
Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
|Data format:||The WinZip (version 9.0) file contains the shapefile for the lake floor interpretation, as well as FGDC compliant metadata. in format Shapefile (version ArcGIS 9.2) Size: 0.629|
|Media you can order:||CD-ROM (Density 650 Mbytes) (format UDF)|
The user must be capable of uncompressing WinZip files. Once uncompressed, the user must have software capable of displaying ESRI shapefile format.