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Research about Arizona, Nevada

Source-linked reports with geographic coverage including Arizona, Nevada.

At least 37 records · Page 2Linked to original sources
USGS2010

Implications of geophysical analysis on basin geometry and fault offsets in the northern Colorado River extensional corridor and adjoining Lake Mead region, Nevada and Arizona

The northern Colorado River extensional corridor and Lake Mead region are characterized by prominent gravity and magnetic anomalies that provide insight into the geometry of extensional basins, amount of vertical and strike-slip offset on faults that bound these basins, and composition of major basement blocks. Although large-magnitude extension throughout the extensional corridor and major strike-slip faulting north of Lake Mead have highly disrupted many basins, most of the older basins (middle to late Miocene) are not associated with prominent geophysical anomalies. Instead, the most conspicuous anomalies (e.g., gravity lows) generally correspond to the younger (late Miocene to recent), structurally more coherent basins. Most of the geophysically expressed basins lie north of Lake Mead and are bounded by Quaternary normal and/or strike-slip fault zones. Both Quaternary faults and geophysically conspicuous basins are largely absent south of Lake Mead, where the only prominent gravity low corresponds to a structurally intact basin filled primarily with halite along the less extended, eastern margin of the corridor. Relatively continuous northeast-trending magnetic anomalies south of Lake Mead, presumably caused by Proterozoic basement rocks, suggest that strike-slip displacement is negligible on many of the major normal faults. In contrast, magnetic anomalies are smeared along the Lake Mead fault system and Las Vegas Valley shear zone. Offset anomalies suggest left-lateral displacement of 12–20 km for the Hamblin Bay fault zone, 12–15 km for the Lime Ridge fault, and 12 km on the Gold Butte fault. These values are compatible with or lower than published estimates based on geologic mapping.

Arizona, Nevada↗
USGS2010

Geometry and kinematics of the eastern Lake Mead fault system in the Virgin Mountains, Nevada and Arizona

The Lake Mead fault system is a northeast-striking, 130-km-long zone of left-slip in the southeast Great Basin, active from before 16 Ma to Quaternary time. The northeast end of the Lake Mead fault system in the Virgin Mountains of southeast Nevada and northwest Arizona forms a partitioned strain field comprising kinematically linked northeast-striking left-lateral faults, north-striking normal faults, and northwest-striking right-lateral faults. Major faults bound large structural blocks whose internal strain reflects their position within a left step-over of the left-lateral faults. Two north-striking large-displacement normal faults, the Lakeside Mine segment of the South Virgin–White Hills detachment fault and the Piedmont fault, intersect the left step-over from the southwest and northeast, respectively. The left step-over in the Lake Mead fault system therefore corresponds to a right-step in the regional normal fault system. Within the left step-over, displacement transfer between the left-lateral faults and linked normal faults occurs near their junctions, where the left-lateral faults become oblique and normal fault displacement decreases away from the junction. Southward from the center of the step-over in the Virgin Mountains, down-to-the-west normal faults splay northward from left-lateral faults, whereas north and east of the center, down-to-the-east normal faults splay southward from left-lateral faults. Minimum slip is thus in the central part of the left step-over, between east-directed slip to the north and west-directed slip to the south. Attenuation faults parallel or subparallel to bedding cut Lower Paleozoic rocks and are inferred to be early structures that accommodated footwall uplift during the initial stages of extension. Fault-slip data indicate oblique extensional strain within the left step-over in the South Virgin Mountains, manifested as east-west extension; shortening is partitioned between vertical for extension-dominated structural blocks and south-directed for strike-slip faults. Strike-slip faults are oblique to the extension direction due to structural inheritance from NE-striking fabrics in Proterozoic crystalline basement rocks. We hypothesize that (1) during early phases of deformation oblique extension was partitioned to form east-west–extended domains bounded by left-lateral faults of the Lake Mead fault system, from ca. 16 to 14 Ma. (2) Beginning ca. 13 Ma, increased south-directed shortening impinged on the Virgin Mountains and forced uplift, faulting, and overturning along the north and west side of the Virgin Mountains. (3) By ca. 10 Ma, initiation of the younger Hen Spring to Hamblin Bay fault segment of the Lake Mead fault system accommodated westward tectonic escape, and the focus of south-directed shortening transferred to the western Lake Mead region. The shift from early partitioned oblique extension to south-directed shortening may have resulted from initiation of right-lateral shear of the eastern Walker Lane to the west coupled with left-lateral shear along the eastern margin of the Great Basin.

Arizona, Nevada↗
USGS2010

Riparian vegetation response to the March 2008 short-duration, High-Flow Experiment— Implications of timing and frequency of flood disturbance on nonnative plant establishment along the Colorado River below Glen Canyon Dam

Riparian plant communities exhibit various levels of diversity and richness. These communities are affected by flooding and are vulnerable to colonization by nonnative species. Since 1996, a series of three high-flow experiments (HFE), or water releases designed to mimic natural seasonal flooding, have been conducted at Glen Canyon Dam, Ariz., primarily to determine the effectiveness of using high flows to conserve sediment, a limited resource. These experiments also provide opportunities to examine the susceptibility of riparian plant communities to nonnative species invasions. The third and most recent HFE was conducted from March 5 to 9, 2008, and scientists with the U.S. Geological Survey's Grand Canyon Monitoring and Research Center examined the effects of high flows on riparian vegetation as part of the overall experiment. Total plant species richness, nonnative species richness, percent plant cover, percent organic matter, and total carbon measured from sediment samples were compared for Grand Canyon riparian vegetation zones immediately following the HFE and 6 months later. These comparisons were used to determine if susceptibility to nonnative species establishment varied among riparian vegetation zones and if the timing of the HFE affected nonnative plant establishment success. The 2008 HFE primarily buried vegetation rather than scouring it. Percent nonnative cover did not differ among riparian vegetation zones; however, in the river corridor affected by Glen Canyon Dam operations, nonnative species richness showed significant variation. For example, species richness was significantly greater immediately after and 6 months following the HFE in the hydrologic zone farthest away from the shoreline, the area that represents the oldest riparian zone within the post-dam riparian area. In areas closer to the river channel, tamarisk (Tamarix ramosissima X chinensis) seedling establishment occurred (<2 percent cover) in 2008 but not to the extent reported in either 2000, a year when experimental summer flows coincided with tamarisk seed production, or in 1986, a year following several years of sustained flooding. The results from the 2008 HFE suggest that riparian vegetation zones subject to intermittent disturbance and near the river under normal dam operations are more susceptible to nonnative species introductions following a disturbance. This study also finds that the timing of an HFE affects the types of species that can become established. For example, HFEs conducted in March are associated with reduced tamarisk seedling establishment compared to disturbances later in the season. Additionally, early season, short-duration flooding that results in vegetation burial may favor clonal species. Along the Colorado River many of these clonal species are native; these species include arrowweed (Pluchea sericea), coyote willow (Salix exigua), and rivercane (Phragmites australis).

Arizona, Nevada↗
USGS2005

Seismic architecture and lithofacies of turbidites in Lake Mead (Arizona and Nevada, U.S.A.), an analogue for topographically complex basins

Turbidites, which have accumulated in Lake Mead since completion of the Hoover Dam in 1935, have been mapped using high-resolution seismic and coring techniques. This lake is an exceptional natural laboratory for studying fine-grained turbidite systems in complex topographic settings. The lake comprises four relatively broad basins separated by narrow canyons, and turbidity currents run the full length of the lake. The mean grain size of turbidites is mostly coarse silt, and the sand content decreases from 11-30% in beds in the easternmost basin nearest the source to 3-14% in the central basins to 1-2% in the most distal basin. Regionally, the seismic amplitude mimics the core results and decreases away from the source. The facies and morphology of the sediment surface varies between basins and suggests a regional progression from higher-energy and possibly channelized flows in the easternmost basin to unchannelized flows in the central two basins to unchannelized flows that are ponded by the Hoover Dam in the westernmost basin. At the local scale, turbidites are nearly flat-lying in the central two basins, but here the morphology of the basin walls strongly affects the distribution of facies. One of the two basins is relatively narrow, and in sinuous sections reflection amplitude increases toward the outsides of meanders. Where a narrow canyon debouches into a broad basin, reflection amplitude decreases radially away from the canyon mouth and forms a fan-like deposit. The fine-grained nature of the turbidites in the most distal basin and the fact that reflections drape the underlying pre-impoundment surface suggest ponding here. The progression from ponding in the most distal basin to possibly channelized flows in the most proximal basin shows in plan view a progression similar to the stratigraphic progression documented in several minibasins in the Gulf of Mexico. Copyright ?? 2005, SEPM (Society for Sedimentary Geology).

Arizona, Nevada↗
USGS2000

Distribution, movements, and habitat use of razorback sucker (Xyrauchen texanus) in a lower Colorado River Reservoir, Arizona-Nevada

Distribution, movements, and habitat use of 10 wild adult razorback suckers ( Xyrauchen texanus ) were examined in Lake Mohave, Arizona-Nevada, from November 1994 through July 1997. Movement rates (0.00-17.35 km d⁻¹) and ranges (x̄ = 39 km) were similar to those for riverine populations. All study fish returned to spawning sites used in previous years, but they also visited other spawning areas. Spawning females were significantly (P = 0.031) more active than males (480 vs. 87 m d⁻¹) and moved substantial distances between spawning sites during peak reproduction (1-28 February). Fish became most active (m d⁻¹, km month⁻¹) after spawning and moved to areas known to support higher algal production. Fish were typically within 50 m (F < 0.001) of shore and at average depths between 3.1 and 16.8 m (range 0.2 to > 30.0 m). Adults were detected throughout the available thermal gradient (12°-30°C), but during summer typically had body temperatures between 18° and 22°C. Vertical movements within the water column showed no correlation with depth or time of day, but seasonal shifts suggest fish may regulate body temperature by seeking specific temperatures during reservoir stratification.

Arizona, Nevada↗
USGS1999

Spring-summer movements of bonytail in a Colorado River reservoir, Lake Mohave, Arizona and Nevada

The bonytail Gila elegans is a large-river minnow (Cyprinid) endemic to the Colorado River system of western North America. The species is federally listed as endangered, its biology poorly understood, and relatively little is known of its movements. Two short-term telemetry studies were conducted during 1996 and 1997 to assess spring-summer temporal and spatial movement patterns in Lake Mohave, Arizona and Nevada, where the largest remaining population of bonytail persists. A total of 20 bonytail were implanted with 90-day sonic transmitters. Ten fish (5 wild-caught from the Lake and 5 cove-reared: 5 females and 5 males) were implanted in May 1996 and additional 10 (7 wild-caught and 3 pond-reared: 2 females and 8 males) were implanted in April 1997, released into the lake immediately after surgery, and tracked approximately weekly through August of both years. Eight fish dispersed immediately after release in 1996, two moved up- and six moved down-lake. The five wild-caught fish moved down-lake as much as 42 km, and four of these (all males) remained in the lower most 5 km while the other (female) occupied an area about 10 km below the release site. Two cove fish moved up lake 15 and 43 km, respectively, while a third moved 4 km down-lake. Two fish were never contacted. Most locations were in shallow water along shorelines, in some instance within inundated stands of riparian vegetation. In 1997, three pond fish were surgically implanted with transmitters and released at Cottonwood Cove, Nevada. Two were not contacted again, and the other was lost 12 days post-release after moving approximately 1.4 km across the lake. Seven wild fish were captured and released at two sites in the lower portion of the lake, and all moved to downstream areas where they remained for the duration of study. Contact was lost with one fish after 3 days and another remained stationary after 13 days; the five others were tracked for 62 to 119 days. These last fish remained in the lower lake and had net movement (displacement from release site to last contact location) that averaged 5.4 km and ranged from 4.7 to 6.9 km. All net displacements were downstream. Cumulative distance traveled averaged 28.9 km and ranged from 19.9 to 33.0 km. Most fish locations during daylight hours were in deep water adjacent to the steep Nevada shore, while nighttime locations were in shallow water along gently sloping Arizona shorelines. Bonytail can move substantial distances in a short time (10s of km in a few days). Fish in both years apparently favored the same areas, where they may remain for weeks. Unmarked bonytail were observed or captured by setting nets in places favored by tagged fish, a significant result since future use of the technique may enhance our ability to monitor reintroductions, locate and document spawning, examine habitat use, and acquire desperately needed brood stock for this critically imperiled species. External tagging techniques developed for juvenile razorback sucker may provide a method of minimizing telemetry induced stress while allowing us to focus sampling on congregation sites.

Arizona, Nevada↗
USGS1999

Principal facts for gravity stations and physical property measurements in the Lake Mead 30' by 60' quadrangle, Nevada and Arizona

The U.S. Geological Survey (USGS) collected 811 gravity stations on the Lake Mead 30' by 60' quadrangle from October, 1997 to September, 1999. These data were collected in support of geologic mapping of the Lake Mead quadrangle. In addition to these new data, gravity stations were compiled from a number of sources. These stations were reprocessed according to the reduction method described below and used for the new data. Density and magnetic susceptibility measurements were also performed on more than 250 rock samples. The Lake Mead quadrangle ranges from 360 to 360 30' north latitude and from 114° to 115° west longitude. It spans most of Lake Mead (see index map, below), the largest manmade lake in the United States, and includes most of the Lake Mead National Recreation Area. Its geology is very complex; Mesozoic thrust faults are exposed in the Muddy Mountains, Precambrian crystalline basement rocks are exhumed in tilted fault blocks near Gold Butte, extensive Tertiary volcanism is evident in the Black Mountains, and strike-slip faults of the right-lateral Las Vegas Valley shear zone and the left-lateral Lake Mead fault system meet near the Gale Hills. These gravity data and physical property measurements will aid in the 3-dimensional characterization of structure and stratigraphy in the quadrangle as part of the Las Vegas Urban Corridor mapping project.

Arizona, Nevada↗
USGS1975

Catalog of earthquakes in the Lake Mead area, Nevada-Arizona, for the period from July 10, 1972, to December 6, 1973

Lake Mead is one of the world's largest reservoirs and was created by the construction of Hoover (formerly Boulder) Dam in the 1930's. Earthquakes were felt in September 1936, a few weeks after Lake Mead had reached its annual peak of about 100 m in maximum water depth. At the request of the Bureau of Reclamation, the Coast and Geodetic Survey began seismic investigations in 1937. A quadripartite net of short-period seismographs was installed in 1942 and operated until the early 1950's. Results of these investigations were reported by Mead and Carder (1941), Jones-(1944), Carder (1945), Carder and Small (1948), and Carder (1970).

Arizona, Nevada↗