Chapter 10: Shallow crustal deformation in the Pahranagat area, southern Nevada

The Pahranagat area lies in the Basin and Range Province of southern Nevada. Paleozoic rocks in the study area were folded and faulted during the Sevier orogeny and subsequently extended prior to deposition of Tertiary strata. Middle Oligocene strata overlie the Paleozoic rocks with pronounced angular unconformity and were deposited on rocks of Late Cambrian through Pennsylvanian age in the eastern part of the study area. Middle Oligocene and Miocene strata unconformably overlie lower Paleozoic and Precambrian strata in the western part of the study area.

In the eastern part of the study area, extension occurred prior to deposition of the middle Oligocene strata; the area was relatively stable between the middle Oligocene and latest Miocene, and there was renewed extension following the latest Miocene to present. There is a significant structural and stratigraphic break in Cenozoic rocks of the western part of the quadrangle where angular unconformities in the Tertiary section indicate extension continued intermittently during the late Oligocene and Miocene.

Faulting and folding that has formed the present Basin and Range topography of the study area is latest Miocene and/or younger in age. Fault scarps in alluvial deposits, active seismicity, and warm springs indicate the area is still tectonically active. The study area lies in a zone of northeast-southwest-trending structures characterized by structural, geophysical, and igneous trends that are referred to herein as the Escalante disrupted zone.