Lake Mead - a view of the Overton Arm of Lake Mead

This view of the Overton Arm of Lake Mead is from the Stewarts Point area. Across the lake, incised alluvial fans extend into the Muddy River Valley (now reservoir) from the Virgin Mountains. The Virgin Mountains consist of complexly faulted and folded rocks of the same sequence exposed in the western Grand Canyon region (Precambrian granitic basement overlain by a mile-thick sequence of Paleozoic rocks). This same sequence also occurs in the Frenchman Mountains near Las Vegas, which has led geologists to postulate that this crustal block was once located at the southern end of the Virgin Mountains. Beginning about 16 million years ago, the Frenchman Mountains crustal block was transported westward along the Lake Mead fault and Las Vegas shear zones to its present location. This kind of tectonic movement was happening throughout the southern Basin and Range Province during this period, producing the ranges and sediment -filled basins we see in the region today (Tingley and others, 2001, Beard and others, 2007).