Authors: Sandra J. Wyld, James R. Nutaitis, and James E. Wright
Series: Open-File Report 18-7
Format: plate: 51 x 38 inches, color, with 3 cross sections and photos; text: 14 pages, b/w
This is a new geologic map of the central East Range, including bedrock and Cenozoic geology. Text on stratigraphic units and structural relations accompanies map. Panels illustrating structures and elements of stratigraphy are included. The study documents several important new discoveries. Ductilely deformed and metamorphosed rocks of the Cambrian Preble Formation underlie the Lee Peak Window, but are not as extensive as previously inferred, and Ordovician fossils thought to be from the Preble are actually from the structurally overlying Ordovician Valmy Formation. A fault between these two units is present everywhere (Lee Peak fault) and probably originated as a Paleozoic thrust (Roberts Mountains thrust?) but was later domed upward, along with Window units, during intrusion of the 165 Ma Lee Peak pluton. Unconformably overlying the Valmy Formation is the Mississippian to Pennsylvanian(?) Inskip Formation, which is extensively deformed by the newly defined Jurassic top-to-the-east Buena Vista ductile shear zone. We distinguish a new unit, the Permian Buena Vista unit, from the upper Inskip Formation. A newly defined dextral strike-slip fault (Jurassic Rockhill Canyon fault, previously shown as part of a “Willow Creek thrust”) is identified in Rockhill Canyon, and separates Paleozoic units listed above from a thin selvage of Havallah Formation overlain by Triassic strata of the Koipato, Star Peak, and Auld Lang Syne Groups. Triassic units were deformed by NW-SE shortening in the Jurassic, primarily manifested by folds and foliation. Jurassic structures (shear zone, strike-slip fault, folds and foliation) are related to shortening in the Fencemaker fold-thrust belt.
The map covers most of the Dun Glen and Natchez Pass 1:24:000-scale quadrangles and the southern portion of the Inskip Canyon and Lee Peak quadrangles.
Geologic mapping was supported by the Tectonics Program of the National Science Foundation and the Geological Society of Nevada.