Abstract

In a report published in 1926, based on reconnaissance study in a wide area including Spring Mountains, Nevada, I suggested that a mass of sheared rubble now exposed at one locality represents rock fragments derived from and overridden by an advancing thrust plate. More recent study establishes clearly that the sheared objects are well-rounded pebbles and cobbles of resistant rock, representing the basal conglomerate unit of a sedimentary formation that was overridden and largely obliterated by movement of a thrust plate during the Sevier orogeny. Careful study of the sheared remnants reveals striking similarities to the basal conglomerate of a Cretaceous(?) formation now exposed in the Frenchman Mountain block, about 25 miles to the east.

Remnants of the Red Spring thrust plate, correctly identified in 1926, were mistakenly interpreted in a later report (Longwell and others, 1965) as a much broken part of the Keystone thrust plate.

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