Surficial Geology and Distribution of Post-Impoundment Sediment of the Western Part of Lake Mead Based on a Sidescan Sonar and High-Resolution Seismic-Reflection Survey, Figure 1.

Figure 2. Generalized geology of the area surrounding Lake Mead. Geology of Arizona is modified from Wilson et al. (1969), and geology of Nevada is modified from Stewart and Carlson (1978). Alluvial is mostly Quaternary and recent unconsolidated alluvial gravel, sand and silt. K-T Volcanics are mostly Cretaceous and Tertiary andesitic and basaltic flows. T Intrusives are mostly Tertiary aged rhyolitic flows and shallow intrusive rocks including diorite and granite. T Sedimentary are Tertiary aged tuffaceous sedimentary rocks. Precambrian includes gneiss and some areas of undivided schist and granite of Precambrian age.