Keystone Thrust Trail in Red Rock Canyon NCA—NBMG Story Map

Story maps are an excellent way to share content in order to help the public, students, teachers, and researchers alike in learning about a specific topic. These story maps make it easy for us to organize our maps, photos, research, and geography to tell a story. Rachel Micander with the Cartography and GIS group at NBMG has recently created a story map featuring the Keystone thrust trail and geology of the area. The story map features photographs of the fantastic geology of the Keystone thrust fault and a short virtual “hike” along the Keystone thrust trail in Red Rock Canyon National Conservation Area! Explore this unique region in more detail here: https://nbmg.maps.arcgis.com/apps/Cascade/index.html?appid=186ff1a40b4a47e7b4ce0605b226c62c

New Geologic Map in Lincoln County

Preliminary Geologic Map of the Lower Pahranagat Lake NW Quadrangle, Lincoln County, Nevada
by Thomas Price, Michael Evans, Mahmud M. Muhammad, Max Hinson, Alexis McIntyre, Alexander Peck, Philip Hahn, and Wanda J. Taylor
Year: 2017
Series: Open-File Report 2017-03
Format: plate: 34.5 x 27.5 inches, color
Scale: 1:24,000
View/Download/Purchase:  http://pubs.nbmg.unr.edu/Prelim-Lower-Pahranagat-Lake-NW-p/of2017-03.htmThe Lower Pahranagat Lake NW quadrangle, Lincoln County, Nevada, includes Paleozoic strata, a Cretaceous-Tertiary sedimentary interval, Cenozoic units, and structures of at least two different deformations.

The exposed Paleozoic formations range from Ordovician Pogonip Group to Devonian Simonson Dolomite. These rocks are mostly carbonate, but some siltstone and sandstone, including the Eureka Quartzite, are interlayered. The Cenozoic units are subdivided into an Oligocene to Miocene section and a Pliocene to Quaternary section. The Oligocene-Miocene section contains mostly ash-flow tuffs that range from the 27.57 Ma Monotony Tuff to the ~15 Ma Kane Springs Wash tuff with minor siliciclastic intervals. The Pliocene-Quaternary section consists of clast-supported conglomerate to clayey sand that was deposited in two different ages, older and younger, of alluvial to fluvial environments.

The older of the two deformations is associated with the Sevier orogeny or associated central Nevada thrust belt and Nevadaplano. The Jurassic or Cretaceous Gass Peak thrust lies to the southeast of the quadrangle and the correlative Pahranagat and Mt. Irish thrusts are exposed to the north. In the quadrangle, this deformation is represented by one small reverse fault exposed in the north and tilting of the Paleozoic rocks. The angle across the Paleogene unconformity is about 35° in the northern and central parts of the quadrangle. A paleo-hill of Paleozoic rocks against which the Tertiary-Cretaceous sedimentary unit through the 22.56 Ma Harmony Hills Tuff are in buttress unconformity occurs in the northern part of the quadrangle. The presence of this paleo-hill suggests notable erosion. The second interval of deformation occurred in the Miocene-Quaternary as shown by normal-, oblique-, and strike-slip faults. The majority of these faults cut all of the exposed tuffs indicating that they are younger than the ~15 Ma Kane Wash Tuff. Based on crosscutting relationships, at least three ages of deformation occurred within the quadrangle: (1) 22.2 and 18.6 Ma, (2) 18.6 to 15.3 Ma, and (3) post 15 Ma. The major post-15 Ma structures are part of the NE-striking, left-lateral Pahranagat shear zone (a.k.a. Pahranagat fault system). Parts of each of three major left-lateral faults of that system are exposed: the Arrowhead Mine fault in the north, the Buckhorn fault in the center, and the Maynard Lake fault in the south. The km-scale Buckhorn syncline lies just north of the Buckhorn fault and folds rocks as young as the ~15 Ma Kane Wash Tuff. This syncline plunges gently NE and is an open fold. The Buckhorn syncline is interpreted as a fault propagation fold related to left-lateral slip along the Buckhorn fault based on subparallel orientations and timing. Small strike-slip duplexes occur along the Arrowhead Mine and Maynard Lake faults. Each duplex occurs near a bend in a strike-slip fault, which suggests that the duplexes accommodate changes in fault strike.

Partial support provided by the U.S. Geological Survey, National Cooperative Mapping Program award number G15AC00157, 2015.

A note from the authors (Department of Geoscience; University of Nevada, Las Vegas): We thank James Faulds and Angela Jayko for their support of this project. We also thank our valuable field assistants Jeremy Miera and Jeffrey Kinney.

New Report—Geology and Geophysics of White Pine and Lincoln Counties

Geology and Geophysics of White Pine and Lincoln Counties, Nevada, and Adjacent Parts of Nevada and Utah: The Geologic Framework of Regional Groundwater Flow Systems
Authors: Peter D. Rowley, Gary L. Dixon, Edward A. Mankinen, Keith T. Pari, Darcy K. McPhee, Edwin H. McKee, Andrew G. Burns, James M. Watrus, E. Bartlett Ekren, William G. Patrick, and Judith M. Brandt
Year: 2017
Series: Report 56
Format: text: 146 pages; 4 plates: color, with cross sections
Scale: 1:250,000
Download/purchase:
http://pubs.nbmg.unr.edu/Geol-geophys-White-Pine-Lincoln-p/r056.htm

This report describes the geologic framework of a >65,000 km2 area that straddles the Nevada-Utah border. The studied region includes most of White Pine and Lincoln counties and adjacent counties in eastern Nevada, as well as parts of Tooele, Juab, Millard, Beaver, and Iron counties in western Utah. This study represents more than a 20-year effort by the Southern Nevada Water Authority (SNWA) to understand the groundwater resources of this part of the Great Basin. This first step, which includes a compilation of all the information on the geologic and geophysical setting, was necessary for hydrological and biological investigations. To understand the geologic framework, we compiled all known geologic mapping at a scale of 1:250,000, and constructed 25 geologic cross sections at the same scale. We also present new geophysical data, consisting of gravity surveys and audiomagnetotelluric (AMT) profiles, plus assembly of available aeromagnetic data, contracted from the U.S. Geological Survey (USGS), as well as additional AMT profiles by the SNWA. This report focuses on two large regional groundwater flow systems: the White River and Great Salt Lake Desert systems. Although the map boundaries presented here bound these aforementioned flow systems, the maps, cross sections, and text are intended to serve as a modern multidisciplinary regional geological and geophysical review, comparable to many old county reports in Nevada and Utah.

View the geospatial PDFs for the four plates that accompany this report:
http://pubs.nbmg.unr.edu/Geol-geophys-White-Pine-Lincoln-p/r056.htm

Plate 1—Geologic map of the northern part of the study area, Nevada and Utah
Plate 2—Geologic map of the southern part of the study area, Nevada and Arizona
Plate 3—Geologic cross sections of the northern part of the study area, Nevada and Utah
Plate 4—Geologic cross sections of the southern part of the study area, Nevada and Arizona

GIS files for these plates will be available soon.

This report was prepared with support from the Southern Nevada Water Authority.

“This report is dedicated to Gary L. Dixon, who died at age 73 from cancer on January 14, 2017 as the manuscript was being reviewed and edited. Gary, a great field geologist, led the 20-year study presented here through the strength of his competence and personality. He began the study when he was a Geologist with the U.S. Geological Survey. After retirement, he continued with it as a consulting geologist. Perhaps more important to his coauthors and many others, we loved Gary and can attribute major parts of our careers to mentorship by him and to collaboration with him. To his wife, Wendy Dixon, and his children, Chris Dixon and Natalie Dixon Pique, he was a loving husband and father and a loyal friend to them and most others he met. His passions were geology, golf, and supporting Wendy’s equally extraordinary career with the U.S. Department of Energy. All of us miss him.” (Report 56)

New Geologic Maps in Clark County: Boulder City and Apex Quadrangles

bc

Preliminary Geologic Map of the Boulder City Quadrangle, Clark County, Nevada

Authors: Seth Dee, Nicholas H. Hinz, R. Ernie Anderson, and Racheal Johnsen
Year: 2016
Series: Open-File Report 16-4
Format: plate: 39 x 29 inches, color; text: 6 pages, some color
Scale: 1:24,000
View/Download/Buy: http://pubs.nbmg.unr.edu/Prel-geol-Boulder-City-quad-p/of2016-04.htm

 A 1:24,000 scale preliminary geologic map of the Boulder City 7.5-minute quadrangle in Clark County, Nevada. This quadrangle covers portions of the southeastern River Mountains, the northern Eldorado Mountains and straddles a segment of the drainage divide between the hydrologically closed Eldorado Valley and the through-flowing Colorado River Basin. Boulder City is located in the northern part of the quadrangle, as is the in-progress Interstate 11, Boulder City Bypass. This publication includes a combination of new mapping and integration with existing mapping by Ernie Anderson.

The bedrock exposures in the quadrangle are dominated by Tertiary plutonic, volcanic, and sedimentary rocks with lesser Proterozoic metamorphic rocks and Paleozoic sedimentary rocks. In the northern Eldorado Mountains the basal volcanic section includes the early to middle Miocene, intermediate to felsic composition Patsy Mine volcanics. The Patsy Mine volcanics are locally intruded by the composite, middle Miocene Boulder City pluton. This pluton is variably hydrothermally altered with actinolite present in altered groundmass and fracture-fill veins. Both the Boulder City pluton and the Patsy Mine volcanics are locally overlain by the middle Miocene Mount Davis volcanics which consist of a syn-extensional, bimodal sequence of lavas and tuffaceous sediments. In the southeastern River Mountains, the Tertiary strata are dominated by the middle Miocene, intermediate to felsic composition Red Mountain volcanics. These rocks are intruded by a middle Miocene granitic stock, which is probably related to widespread hydrothermal alteration of the Red Mountain volcanics. Locally overlying the Red Mountain volcanics are the less altered, intermediate to silicic, volcanics of Bootleg Wash, and unaltered Mount Davis volcanics.

The bedrock in the northern Eldorado Mountains is faulted by numerous north-striking, down-to-east and down-to-west normal faults. The northeast-striking, sinistral Hemenway Wash fault transects the northwest quarter of the quadrangle, separating the Eldorado Mountains from the River Mountains. The Hemenway Wash fault is one of the faults that makes up the >100 km-long, Lake Mead Fault System. In the northernmost Eldorado Mountains, fault strikes curve from N-S to NW and to E-W as they approach the Hemenway Wash fault zone, possibly due to oroclinal flexure. Provisional analysis of new geochronologic and geochemical data acquired in this study indicate that the plutonic and volcanic strata exposed in the southeastern River Mountains may correlate directly to strata in the northern Eldorado Mountain, providing a means to evaluate a range of possible displacements across the Hemenway Wash fault.

Surficial sediments in the quadrangle are largely alluvial fan and pediment deposits ranging from historic to Pliocene in age. Early Pleistocene to late Pliocene surficial deposits are characterized by 2+ m thick pedogenic carbonate horizons, which form resistant geomorphic surfaces on the east side of the Eldorado basin and cap many of the bedrock highlands in the Eldorado range. Fan deposits eroded from altered Boulder City plutonic rocks or from Miocene basin sediments may contain redistributed actinolite-bearing clasts. One possible fault scarp was observed in a late to middle Pleistocene aged fan. No other evidence for Quaternary faulting was recognized in the quadrangle.

This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G15AC00240, 2016.

apexPreliminary Geologic Map of the Apex Quadrangle, Clark County, Nevada

Author: Robert G. Bohannon
Year: 2016
Series: Open-File Report 16-3
Format: plate: 31 x 32 inches, color; text: 5 pages, color
Scale: 1:24,000
View/Download/Buy: http://pubs.nbmg.unr.edu/Prelim-geol-Apex-quad-p/of2016-03.htm

The Apex quadrangle (1:24,000 scale) is centered approximately 22.5 km northeast of downtown Las Vegas in Clark County, Nevada. Rocks in the quadrangle are exclusively sedimentary and include a mostly conformable sequence of Paleozoic continental shelf and platform rocks in its north half. The south half of the quadrangle is mostly Miocene interior-continental-basin deposits. Dissected alluvial deposits of Quaternary and latest Tertiary age, only the oldest of which are consolidated, discontinuously cover large lowland parts of the quadrangle. The Paleozoic rocks are deformed and in some places overturned by Mesozoic thrust faults associated with the Late Cretaceous Sevier Orogenic disturbance. A large east-vergent thrust fault with a northeast orientation, the Dry Lake Thrust, cuts the eastern half of the quadrangle, where it is mostly concealed by post-Cretaceous deposits. The thrust juxtaposes lower Paleozoic shelf rocks in the hanging wall above upper Paleozoic continental platform rocks in the footwall. Tertiary normal faults are also common and are mostly oriented northeast where they cut Paleozoic rocks. The Miocene beds, most of which post-date the northeast normal faults, are deformed by a few east-west or east-northeast-oriented faults and numerous small folds that are associated with them. The younger faults might be associated with very late-stage movement on the Las Vegas Valley shear zone which projects into the quadrangle from beneath Las Vegas Valley to the east, but the shear zone is otherwise concealed by the Miocene deposits.

Earthquake Faults in Las Vegas—video on News 3

Late Quaternary faults in Las Vegas are in need of a modern state-of-the-art analysis of their earthquake potential. This news clip, prepared by Channel 3 in Las Vegas, reviews some of the Las Vegas Valley faults with a local reporter and how we can wisely develop around faults with ground rupture potential. A resident is featured on the clip that was unaware of the fault and earthquake hazard potential in Las Vegas. Unfortunately, this may be the norm and not the exception. It underscores the need for all Nevadans to be aware of their earthquake risks and do what they can to reduce them (please see http://www.nbmg.unr.edu/dox/sp27.pdf for mitigation information). Practicing the safest response to the next Nevada earthquakes can help prevent injuries from those events. Thus, we encourage everyone to sign up for the annual Nevada earthquake drill, the Great Nevada ShakeOut in October, and to practice Drop, Cover, and Hold during that exercise (see http://shakeout.org/nevada/).

…message from Craig dePolo

Link to the video:

http://www.mynews3.com/content/news/story/Believe-it-There-are-many-earthquake-faults-in/C68FGas5YUyayNmbk1bPCg.cspx#.U8WG1NvZHV0.email