Abstract

A flat thrust fault of middle or later Tertiary age, believed to have followed roughly the contact of later pre-Cambrian sediments with earlier pre-Cambrian metamorphic rocks, is well exposed throughout the Virgin Spring area, about 10 miles square, in the Black Mountains east of Death Valley. On this thrust later pre-Cambrian, Cambrian, and Tertiary rocks have moved relatively westward for an unknown distance. The rocks of the overthrust plate are broken into innumerable blocks and slices, which are thrust over one another to form an extremely complex mosaic. This assemblage of blocks is named the Amargosa chaos, and the flat fault upon which the chaos lies is named the Amargosa thrust. The chaos is divided into the Virgin Spring, Calico, and Jubilee facies, each characterized by certain kinds of rock. The Amargosa thrust and chaos are folded into several plunging anticlines, of northwesterly trend, along whose crests the earlier pre-Cambrian rocks below the thrust are exposed.

Lying unconformably upon the folded thrust and chaos is the Funeral fanglomerate, probably of late Pliocene age, which consists of fanglomerates and basaltic lava flows.

These rocks are deformed by folds and faults so recent that they are still reflected in the topography; Death Valley in the Virgin Spring area is primarily a syncline, modified by faulting, in the Funeral fanglomerate.

Features similar to the Amargosa thrust and chaos occur throughout an area of at least 8000 square miles that borders and includes the Death Valley trough.

The present paper deals mainly with the structure of the Virgin Spring area but it, also notes related structures elsewhere in the Death Valley region, outlines the stratigraphy of the region, and describes a geologic section across it.

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