A complex pattern of active faults occurs in the southern Amargosa Desert, southern Nye, County, Nevada. These faults can be grouped into three main fault systems: (1) a NE-striking zone of faults that forms the southwest extension of the left-lateral Rock Valley fault zone, in the much larger Spotted Range-Mine Mountain structural zone, (2) a N-striking fault zone coinciding with a NNW-trending alignment of springs that is either a northward continuation of a fault along the west side of the Resting Spring Range or a N-striking branch fault of the Pahrump fault system, and (3) a NW-striking fault zone which is parallel to the Pahrump fault system, but is offset approximately 5 km with a left step in southern Ash Meadows. These three fault zones suggest extension is occurring in an E-W direction, which is compatible with the {approximately}N10W structural grain prevalent in the Death Valley extensional region to the west.

This report summarizes results on surveys taken by the U.S. Geological Survey made to determine the seismic velocity, electrical resistivity, and preliminary geology of rock in the U12n.03 tunnel, Nevada Test Site.

This is a photo-geologic map of the Skull Mountain Quadrangle at the Nevada Test Site.

Geologic map of the Topopah Spring Southwest quadrangle, Nevada with notations for specific topographic features and profile views. Scale 1:24,000.

The Topopah Spring and Timber Mountain 15-minute quadrangles comprising about 500 square miles in southern Nye County, Nev., are bounded by longitudes 116°15' W. and 116°30' W. and by latitudes 36°45' N. and 37°15' N. (fig. 1) The quadrangles are mostly within the Nevada Test Site and are approximately 90 miles northwest of Las Vegas (fig. 1). Lathrop Wells, the nearest town, is about 10 miles south of the southern boundary of the Topopah Spring quadrangle.

The following report covers geological studies on the USGS and Rainier tunnel areas in the Nevada Test Site.