Mapping the floor of Lake Mead (Nevada and Arizona): Preliminary discussion and GIS data release, USGS Open-File Report 03-320

INTRODUCTION

The U.S. Geological Survey in cooperation with the Lake Mead/Mohave Research Institute, University of Nevada, Las Vegas completed a detailed geophysical mapping of the floor of Lake Mead during 1999, 2000, and 2001. The 1999 survey covered the Boulder Basin section of the lake, the 2000 survey focused on the northwestern portion of Las Vegas Bay, and the 2001 survey covered the eastern

Figure 1. Map showing the location of the study area and survey tracklines.

part of the lake (Fig. 1). Results from these surveys have been presented in several reports (Cross and Twichell, 2003a; 2003b; 2003c; Twichell and others, 1999; 2001); however, here the three data sets have been integrated and are presented as a composite of the entire lake. This Geologic discussion section provides a brief geologic overview of the floor of Lake Mead, as well as summarizing some of the findings resulting from these surveys. This information is provided to provide a geologic perspective for the GIS that accompanies this report.

Lake Mead started to fill following the completion of Hoover Dam in 1935, and since then has supplied water to agricultural, industrial, and municipal users. The multiple uses of the lake have led to a high degree of interest in the lake. Although much of the interest is in the quality of water within the lake, there is also interest in the geology of the lake floor. Water managers are interested in the distribution and amount of sediment that has accumulated in the lake since impoundment to understand changes in the holding capacity of the reservoir. For these reasons, this geophysical mapping program was designed to create a near-complete coverage of the lake floor using sidescan-sonar in water depth greater than about 5-10 m, and to map the distribution and thickness of post-impoundment sediment throughout the lake as derived from high-resolution seismic-reflection profiles. The map and data products derived from these datasets are intended to serve as base maps for other geological and geochemical studies of the lake.

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