Abstract: Tertiary Structural Development of Southern Egan Range, Nevada
The lower Tertiary Sheep Pass Formation lies unconformably on rocks of Mississippian through Early Permian age. Prior to deposition of the Sheep Pass at least part of the area had been broken by near-vertical reverse faults and by the large east- and northeast-trending Shingle Pass normal fault. An erosional topography of moderate relief had developed and large blocks of upper Paleozoic rocks had slid into the incipient lake basins. Renewed structural activity during Oligocene and Miocene times, the initial phase again marked by the emplacement of large slide blocks, resulted in great displacement on the Shingle Pass fault and newly developed, moderately dipping (31 to 56°) normal faults. Displacement of about 3.9 mi (6 km), including a major component of strike slip occurred on the largest of the new normal faults (Ninemile fault).
During late Tertiary time the older fault system was superseded by the present Basin-and-Range pattern, the rocks were tilted an average of 22° to the east-southeast, and the range began to achieve its present form. Displacement on the main Basin-and-Range faults has continued to the present, as shown by the presence of a fault in the recent alluvium all along the west front of the southern Egan Range, and has resulted in an additional 9° eastward tilt of the range during the Quaternary.
AAPG Search and Discovery Article #90964©1978 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah