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.

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

Introduction: The chemical character of ground water depends to a large degree upon the character of the rock formations through which the water moves. The composition of the water is the result of several solutional and decompositional processes.

From abstract: Numerous discontinuous layers of opal are interbedded with a gently-dipping series of vitric tuff and ash which is at least 300 feet thick. The tuff and ash are capped by a dark, vesicular basalt in the eastern part of the area and by a thin layer of terrace gravels in the area along the west side of Virgin Valley.