Eureka County Research Articles

Identifying spatially and temporally transferrable surrogate measures of species richness

We developed a transferable method to identify indicator species and environmental variables that explain considerable variation in species richness. We applied this method to birds and butterflies and conducted novel, rigorous external evaluations of the spatial and temporal transferability of such indicator species. We collected data in the central Great Basin (Lander, Nye, and Eureka Counties, Nevada) and western Great Basin (Mono County, California and Mineral, Douglas, and Lyon Counties, Nevada), United States. We used Bayesian model selection to identify sets of five species that best explained observed variation in species richness of the same or the other taxonomic group in either subregion. We then built random forest models that included only the five identified indicator species and externally tested these models with new data from the other subregion (central or western Great Basin) or a later time in the same subregion. We compared the predictive accuracy of indicator-species only models to that of models based on environmental variables or on both indicator species and environmental variables. In external evaluations, models based on same-taxon indicator species predicted 34–52% of the variation in species richness of birds and 40–70% of the variation in species richness of butterflies. Comparable models based on environmental variables predicted 11–46% of the variation in species richness of birds and 12–67% of the variation in species richness of butterflies. Models based on same-taxon indicator species predicted more variation in species richness than those based on environmental variables in seven of eight cases. Our results suggested that the predictive accuracy and spatial and temporal transferability of models based on indicator species can exceed that of models based on environmental variables. If mechanistic responses to environmental change are consistent through time, tracking the occurrence of a subset of an assemblage during periods of environmental change may allow inference to species richness of the assemblage.

Early Permian conodont fauna and stratigraphy of the Garden Valley Formation, Eureka County, Nevada

The lower part of the Garden Valley Formation yields two distinct conodont faunas. One of late Asselian age dominated by Mesogondolella and Streptognathodus and one of Artinskian age dominated by Sweetognathus with Mesogondolella. The Asselian fauna contains the same species as those found in the type area of the Asselian in the southern Urals including Mesogondolella dentiseparata, described for the first time outside of the Urals. Apparatuses for Sweetognathus whitei, Diplognathodus stevensi, and Idioprioniodus sp. are described. The Garden Valley Formation represents a marine pro-delta basin and platform, and marine and shore fan delta complex deposition. The fan-delta complex was most likely deposited from late Artinskian to late Wordian. The Garden Valley Formation records tremendous swings in depositional setting from shallow-water to basin to shore.

Projecting current and future location, quality, and connectivity of habitat for breeding birds in the Great Basin

We estimated the current location, quality, and connectivity of habitat for 50 species of breeding birds in four mountain ranges in the central Great Basin (Lander, Nye, and Eureka Counties, Nevada) and projected the future location, quality, and connectivity of habitat for these species given different scenarios of climate‐induced land‐cover change. In the United States, such models are relevant to federally mandated management of wild animals by state‐level agencies. We sampled birds during the breeding seasons of 2001–2009 with fixed‐radius point counts. For each species, we used boosted regression trees to model incidence (proportion of years a location was surveyed in which the species was present) as a function of topography and current land cover and climate. To assess model fit, we calculated the proportion of binomial deviance explained. We used cross‐validation to estimate the predictive accuracy of the models. We applied the conservation planning program Zonation to identify locations where incidences of multiple species were maximized through time given current land cover and two scenarios of land‐cover change, expansion of pinyon–juniper woodland into sagebrush shrubsteppe and contraction of riparian woodland. Models based on a set of 13 covariates derived from remotely sensed data had some predictive capacity for 41 of 50 species. Model outputs suggested substantial changes in amount of habitat for many species following projected expansion of pinyon–juniper woodland, but less pronounced changes following projected contraction of riparian woodland. Zonation analyses indicated that the spatial distribution of the highest‐quality habitat for the avian assemblage was relatively consistent through time under both scenarios. Breeding birds in the Great Basin commonly are grouped in management plans on the basis of their general association with land‐cover classes such as pinyon–juniper woodland, sagebrush shrubsteppe, and riparian woodland. However, even within these groups, the environmental attributes that explained a high proportion of variation in species' incidences and the projected responses to different scenarios of land‐cover change varied considerably among species.

Intraseasonal variation in survival and probable causes of mortality in greater sage‐grouse Centrocercus urophasianus

The mortality process is a key component of avian population dynamics, and understanding factors that affect mortality is central to grouse conservation. Populations of greater sage‐grouse Centrocercus urophasianus have declined across their range in western North America. We studied cause‐specific mortality of radio‐marked sage‐grouse in Eureka County, Nevada, USA, during two seasons, nesting (2008‐2012) and fall (2008‐2010), when survival was known to be lower compared to other times of the year. We used known‐fate and cumulative incidence function models to estimate weekly survival rates and cumulative risk of cause‐specific mortalities, respectively. These methods allowed us to account for temporal variation in sample size and staggered entry of marked individuals into the sample to obtain robust estimates of survival and cause‐specific mortality. We monitored 376 individual sage‐grouse during the course of our study, and investigated 87 deaths. Predation was the major source of mortality, and accounted for 90% of all mortalities during our study. During the nesting season (1 April ‐ 31 May), the cumulative risk of predation by raptors (0.10; 95% CI: 0.05‐0.16) and mammals (0.08; 95% CI: 0.03‐013) was relatively equal. In the fall (15 August ‐ 31 October), the cumulative risk of mammal predation was greater (M(mam) = 0.12; 95% CI: 0.04‐0.19) than either predation by raptors (M(rap) = 0.05; 95% CI: 0.00‐0.10) or hunting harvest (M(hunt) = 0.02; 95% CI: 0.0‐0.06). During both seasons, we observed relatively few additional sources of mortality (e.g. collision) and observed no evidence of disease‐related mortality (e.g. West Nile Virus). In general, we found little evidence for intraseasonal temporal variation in survival, suggesting that the nesting and fall seasons represent biologically meaningful time intervals with respect to sage‐grouse survival.

Geographic Variation in Liver Metal Concentrations of Greater Sage-Grouse

Abstract Populations of greater sage-grouse (Centrocercus urophasianus) have declined throughout the species' range. We evaluated metal concentrations in livers sampled from greater sage-grouse collected from hunters in Eureka County, Nevada, during autumn of 2008 and 2010. We make local comparisons of metal concentrations between two populations of greater sage-grouse in Eureka County, as well as regional comparisons with previously reported values for greater sage-grouse collected in Wyoming and Montana. With one exception, tissue concentrations of lead, arsenic, and mercury were below method detection limits. Mean concentrations of iron, molybdenum, and zinc differed between the two Nevada populations, and magnesium, cadmium, molybdenum, and selenium differed between greater sage-grouse in eastern Nevada, and values reported for Wyoming and Montana. In contrast, we found no evidence for local variation in magnesium, copper, cadmium, or selenium, or for regional variation in iron, zinc, or copper. Of particular interest were low selenium concentrations in our study system relative to Wyoming and Montana. Some individuals in our study returned liver selenium values considered consistent with selenium deficiency in domestic poultry. This research adds to the small body of literature on background contaminant levels in greater sage-grouse, and provides evidence for geographic variation in metal concentrations at local and regional scales.

Remembering First Oil in Nevada

In June 1954 Nevada became the twenty-ninth oil-producing state in the United States (Picard 1955). Interestingly, production was from volcanic rocks from the open-hole interval 6,450 to 6,730 ft (1,966 to 2,051 m) in the Oligocene Garrett Ranch volcanics, an unexpected reservoir in the kind of rocks rarely productive anywhere in the world. The pour-point (65-80° F) and gravity (26-29° API) of the crude were high, similar to oils found in the Eocene Green River Formation of the Uinta Basin, northeast Utah. Cumulative production in the field through September 1978 was 3.3 million barrels of oil. An early estimate of ultimate primary reserves was four million barrels of oil (Bortz and Murray, 1979). The trap is a faulted truncated wedge of Oligocene and Cretaceous-Eocene rocks with a top seal of impermeable valley fill, a bottom seal of Paleozoic rocks, and an east-side seal formed by a basin boundary fault and impermeable Paleozoic rocks. The new field in Railroad Valley of east-central Nevada, finally totaling fourteen producing wells, was called Eagle Springs after the locality and the name of the discovery well drilled by the Shell Oil Company. Twenty-two years after the Eagle Springs discovery a larger oil field, Trap Spring, was discovered by Northwest Exploration Company less than ten miles west of Eagle Springs, in Tertiary ash-flow tuffs. Two hundred dry holes had been drilled in Nevada between the two discoveries. In 1982, six years after the Trap Spring discovery, Amoco Production Company drilled the first well outside of Railroad Valley at Blackburn field on the east side of Pine Valley in Eureka County. Blackburn, a structural trap above a Tertiary low-angle extensional fault, produces from Devonian reservoirs. In 1983, Northwest Production brought in the Grant Canyon field about 10 mi (6 km) south of Eagle Springs. The oil reservoir of Devonian carbonates there is entrapped in a ‘buried-hill’. The discovery in 2004 of the Covenant field in Central Utah, because of similarities to large oil fields in the thrust belt of Wyoming and Utah and some resemblance to the Nevada fields of the Great Basin, ignited a frenzy of leasing which still goes on when land is available. Located along the thrust-belt (hingeline), Covenant produces oil from the Jurassic Navajo Sandstone that apparently originated in the Paleozoic.

New and revised species of the aulacopleurid trilobite Maurotarion from the Lower Devonian (Pragian) of Nevada

Deep water silicified trilobite faunas occur in argillaceous limestones of the Lower Devonian (Pragian) Wenban Limestone in the Cortez Mountains, Eureka County, central Nevada, USA. Trilobites occur as a stratigraphic series of three low diversity assemblages, including the odontopleurids Nevadaprusia Adrain, Chatterton, and Kloc, 2008, and Kettneraspis Prantl and Přibyl, 1949, the phacopids Paciphacops Maksimova, 1972, and an unnamed new genus, undetermined dalmanitids, a tropidocoryphid, and the brachymetopid Mystrocephala Whittington, 1960. Aulacopleurids are common elements of all three assemblages and, unusually, are represented by multiple articulated silicified specimens, permitting a complete assessment of the holaspid morphology of some of the species. All belong to the genus Maurotarion Alberti, 1969, and new species are M. chrysion, M. fooi, and M. wenbanense. Maurotarion periergum (Haas, 1969) was described on the basis of a few fragmentary sclerites but is now represented by multiple articulated dorsal exoskeletons.

Use of guilds for modelling avian responses to vegetation in the Intermountain West (USA)

ABSTRACTAim Individually focused conservation management of many species is expensive and logistically impractical. Mesofilter conservation methods may facilitate the simultaneous management of multiple species. We used data on distributions of two sets of avian guilds, based on dependence on riparian vegetation and on nest location, to relate occurrence rates to environmental variables. Variables were selected by expert opinion and are likely to be affected by changes in climate and land use.Location Data were collected from 2001–06 in four adjacent mountain ranges in the central Great Basin (Lander, Nye and Eureka counties, Nevada, USA): the Shoshone Mountains and the Toiyabe, Toquima and Monitor ranges.Methods Data on occurrence of birds, vegetation composition and vegetation structure were obtained in the field. Geographical coordinates and the normalized difference vegetation index were derived from a digital elevation model and a satellite image. To construct a general model for guilds as a whole, while allowing flexibility for variation in the functional responses of individual species, we applied multivariate adaptive regression splines.Results The predictive capacity of expert knowledge of relationships between birds and vegetation was inconsistent. Latitude, longitude and elevation may constrain the response of some guilds to changes in vegetation structure and composition. Guild‐based models were useful for modelling species with sparse distributions, which are difficult to model individually. In essence, this method supplements models for the individual species with patterns for the guild to which they belong.Main conclusions Guilds of birds appeared to have predictable associations with selected attributes of vegetation structure and composition. The criteria by which species are grouped into guilds may affect the success of predictions and management interventions. Our derived models offer the potential to predict effects on the avifauna of management or climate‐driven change in vegetation.

Matioliite, the Mg-analog of burangaite, from Gentil mine, Mendes Pimentel, Minas Gerais, Brazil, and other occurrences

Matioliite, ideally NaMgAl 5 (PO 4 ) 4 (OH) 6 ·2H 2 O, occurs as a secondary hydrothermal mineral in the Gentil mine granite pegmatite, Mendes Pimentel Co., Minas Gerais, Brazil. Some crystals are zoned to more Fe-rich compositions with an Fe 2+ :Mg ratio of approximately 1:1, corresponding to an intermediate member of the burangaite-matioliite solid-solution series. Matioliite is intimately associated with fluorapatite, crandallite, and zoned gormanite-souzalite cystals. The mineral forms prismatic to tabular crystals, up to 1 mm long. Matioliite is transparent and displays a vitreous luster; it is blue to colorless with a white streak. It is non-fluorescent. Mohs hardness is about 5. Calculated density is 2.948 g/cm 3 . Matioliite is biaxial negative, η α = 1.597(2), η β = 1.627(2), η γ = 1.632(1) (white light), 2V (meas.) = 43(2)°, 2V (calc.) = 44°, dispersion r > v, orientation X = b, Z ^ c = 6°. Pleochroism is Y > X > Z, X = light blue to colorless, Y = blue, Z = colorless. The empirical formula is (Na 0.94 Ca 0.01 ) Σ0.95 (Mg 0.88 Fe 2+ 0.11 Mn 0.01 ) Σ1.00 (Al 4.84 Fe 3+ 0.13 ) Σ4.97 (PO 4 ) 4.03 (OH) 5.76 ·2H 2 O. The mineral is monoclinic, space group C2/c, a = 25.075(1) Å, b = 5.0470(3) Å, c = 13.4370(7) Å, β = 110.97(3)°, V = 1587.9(4) Å 3 , Z = 4. Crystal-structure determination was carried out and showed it is isostructural with burangaite, dufr énite, and natrodufrénite. Both the description and the name were approved by the CNMMN-IMA (Nomenclature Proposal 2005-011). The .magnesium analog of burangaite. described from the Gold Quarry mine, Carlin-trend, Eureka County, Nevada; “burangaite” from Hochgosch, Millstätter See-Rücken, Kärnten, Austria; and .burangaite. described from Córrego Pomarolli, Linópolis, Divino das Laranjeiras, Minas Gerais, Brazil, are probably matioliite.

A new variety of Draba pedicellata and a lectotype for D. cusickii (Brassicaceae)

Abstract A new variety of Draba pedicellata and a lectotype for D. cusickii (Brassicaceae). Brittonia 56: 107–114. 2004.—A closely related group of Great Basin endemic drabas, Draba cusickii O. E. Schulz, D. sphaeroides Payson, and D. pedicellata (Rollins & R. A. Price) Windham, are described, keyed, and discussed in order to put D. pedicellata var. wheelerensis N. H. Holmgren, var. nov. in perspective. Draba cusickii is endemic to Steens Mountain of southeastern Oregon, and D. sphaeroides is known only from three mountain ranges in Elko County, Nevada, whereas D. pedicellata is more widespread in mountain ranges of eastern Nevada in Elko, Eureka, Nye, and White Pine counties. Draba pedicellata var. pedicellata occupies most of the range of the species, with var. wheelerensis being restricted to the Snake Range, just to the east of the range of the typical variety.

NEVADAITE, (Cu2+, , Al, V3+)6 [Al8 (PO4)8 F8] (OH)2 (H2O)22, A NEW PHOSPHATE MINERAL SPECIES FROM THE GOLD QUARRY MINE, CARLIN, EUREKA COUNTY, NEVADA: DESCRIPTION AND CRYSTAL STRUCTURE

Nevadaite, (Cu 2+ , □, Al, V 3+ ) 6 (PO 4 ) 8 F 8 (OH) 2 (H 2 O) 22 , is a new supergene mineral species from the Gold Quarry mine, near Carlin, Eureka County, Nevada, U.S.A. Nevadaite forms radiating clusters to 1 mm of prismatic crystals, locally covering surfaces more that 2 cm across; individual crystals are elongate on [001] with a length:width ratio of >10:1 and a maximum diameter of ~30 μm. It also occurs as spherules and druses associated with colorless to purple-black fluellite, colorless wavellite, strengite–variscite, acicular maroon-to-red hewettite, and rare anatase, kazakhstanite, tinticite, leucophosphite, torbernite and tyuyamunite. Nevadaite is pale green to turquoise blue with a pale powder-blue streak and a vitreous luster; it does not fluoresce under ultraviolet light. It has no cleavage, a Mohs hardness of ~3, is brittle with a conchoidal fracture, and has measured and calculated densities of 2.54 and 2.55 g/cm 3 , respectively. Nevadaite is biaxial negative, with α 1.540, β 1.548, γ 1.553, 2 V (obs.) = 76°, 2 V (calc.) = 76°, pleochroic with X pale greenish blue, Y very pale greenish blue, Z blue, and with absorption Z ≫ X > Y and orientation X = c , Y = a , Z = b. Nevadaite is orthorhombic, space group P 2 1 mn , a 12.123(2), b 18.999(2), c 4.961(1) A, V 1142.8(2) A 3 , Z = 1, a:b:c = 0.6391:1:0.2611. The strongest seven lines in the X-ray powder-diffraction pattern [ d in A(I)( hkl )] are: 6.077(10)(200), 5.618(9)(130), 9.535(8)(020), 2.983(6)(241), 3.430(4)(041), 2.661(4)(061), and 1.844(4)(352). A chemical analysis with an electron microprobe gave P 2 O 5 32.54, Al 2 O 3 27.07, V 2 O 3 4.24, Fe 2 O 3 0.07, CuO 9.24, ZnO 0.11, F 9.22, H 2 O (calc.) 23.48, OH ≡ F–3.88, sum 102.09 wt.%; the valence states of V and Fe, and the amount of H 2 O, were determined by crystal-structure analysis. The resulting empirical formula on the basis of 63.65 anions (including 21.65 H 2 O pfu ) is (Cu 2.00 2+ Zn 0.02 V 0.98 3+ Fe 0.01 3+ Al 1.15 ) ∑ 4.16 Al 8 P 7.90 O 32 [F 8.37 (OH) 1.63 ] ∑10 (H 2 O) 21.65 . The crystal structure of nevadaite was solved by direct methods and refined to an R index of 4.0% based on 1307 observed reflections collected on a four-circle diffractometer with Mo K α X-radiation. The structure consists of ordered layers of vertex-sharing octahedra and tetrahedra alternating with layers of disordered vertex-sharing and face-sharing octahedra in the b direction. [Alϕ 5 ] chains of octahedra are decorated by (PO 4 ) tetrahedra that share vertices with octahedra adjacent in the chain. These chains link in the c direction by sharing vertices between octahedra and tetrahedra to form an ordered layer of the form [Al 8 (PO 4 ) 8 F 8 (H 2 O) 8 ]. In the disordered layer, octahedral containing positionally disordered Cu 2+ , V 3+ , Al and □ (vacancy) share trans faces to form columns that link by sharing octahedron vertices to form ribbons extending in the c direction; the resulting layer has the form {(Cu 2 2+ □ 2 V 3+ ,Al) ∑6 (H 2 O) 12 (OH) 2 (H 2 O) x }, x ≈ 2. The layers link in the b direction by sharing vertices between octahedra and tetrahedra. Although decorated chains topologically equivalent to that in nevadaite are common in many oxysalt minerals, its chain is geometrically distinct from those topologically equivalent chains. The M – M linkage along the [ M ϕ 5 ] chains in most minerals take place through trans vertices of the octahedra, with one example of linkage through cis vertices; in nevadaite, the M – M linkage involves both trans and cis vertices, as does the chain in slavikite. In most of these decorated chains, alternate tetrahedra along the chain occur either in a trans or a cis arrangement. In nevadaite and slavikite, the tetrahedra are arranged in both trans and cis arrangements; the arrangements in these two minerals are geometrically distinct, however.

Poracanthodid acanthodian from the Upper Silurian (Pridoli) of Nevada

ABSTRACT Dissociated remains of the acanthodian Poracanthodes punctatus are described from Upper Silurian (Pridoli) limestones of the Roberts Mountains Formation at Pete Hanson Creek, Eureka County, Nevada. The vertebrate microremains in sample residues comprise scales, a dentigerous jaw bone fragment, and a fin spine fragment assigned to P. punctatus, plus one possible acanthothoracid placoderm scale. Some macroremains from the same locality are also assigned to P. punctatus. This taxon has been nominated as a zone fossil for the Silurian vertebrate biozonal scheme, and its presence has been recorded throughout the circum-Arctic region. Identification of the taxon in Nevada extends its known geographic range.

Structural Controls on Carlin-Type Gold Mineralization in the Gold Bar District, Eureka County, Nevada

Structural Controls on Carlin-Type Gold Mineralization in the Gold Bar District, Eureka County, Nevada

Structural Controls on Carlin-Type Gold Mineralization in the Gold Bar District, Eureka County, Nevada

The Gold Bar district in the southern Roberts Mountains, 48 km northwest of Eureka, Nevada, contains one main deposit (Gold Bar), five satellite deposits, and other resources. Approximately 0.5 Moz of gold have been recovered from a resource of 1,639,000 oz of gold in Carlin-type gold deposits in lower plate, miogeoclinal carbonate rocks below the Roberts Mountains thrust. Host rocks are unit 2 of the Upper Member of the Devonian Denay Formation and the Bartine Member of the McColley Canyon Formation. Spatial and temporal relations between structures and gold mineralization indicate that both pre-Tertiary and Tertiary structures were important controls on gold mineralization. Gold mineralization occurs primarily along high-angle Tertiary normal faults, some of which are reactivated reverse faults of Paleozoic or Mesozoic age. Most deposits are localized at the intersection of northwest- and northeast-striking faults. Alteration includes decalcification, and to a lesser extent, silicification along high-angle faults. Jasperoid (pervasive silicification), which formed along most faults and in some strata-bound zones, accounts for a small portion of the ore in every deposit. In the Gold Canyon deposit, a high-grade jasperoid pipe formed along a Tertiary normal fault which was localized along a zone of overturned fault-propagation folds and thrust faults of Paleozoic or Mesozoic age.

Clay alteration and gold deposition in the Genesis and Blue Star deposits, Eureka County, Nevada

The Genesis and Blue Star sedimentary rock-hosted gold deposits occur within the 40-mile-long Carlin trend and are located in Eureka County, Nevada. The deposits are hosted within the Devonian calcareous Popovieh Formation, the siliciclastic Rodeo Creek unit and the siliciclastic Vinini Formation. The host rocks have undergone contact metamorphism, decalcification, silicification, argillization, and supergene oxidation.Detailed characterization of the alteration patterns, mineralogy, modes of occurrence, and associated geochemistry of clay minerals resulted in the following classifications: least altered rocks, found distal to the orebody, consisting of both metamorphosed and unmetamorphosed host rock that has not been completely decalcified; and altered rocks, found proximal to the orebody that have been decalcified. Altered rocks are classified further into the following groups based on clay mineral content: silicic, 1 to 10 percent clay; silicic-argillic, 10 to 35 percent clay; and argillic, 35 to 80 percent clay. Clay species identified are 1M illite, 2M 1 illite, kaolinite, halloysite, and dioctahedral smectite.An early hydrothermal event resulted in the precipitation of euhedral kaolinite and at least one generation of silica. This event occurred contemporaneously with decalcification which increased rock permeability and porosity. A second clay alteration event resulted in the precipitation of hydrothermal 1M illite which replaced hydrothermal kaolinite and is associated with gold deposition. Silver and silica deposition is also associated with this phase of hydrothermal alteration.Hydrothermal alteration was followed by supergene alteration which resulted in the formation of supergene kaolinite, halloysite, and smectite as well as the oxidation of iron-bearing minerals. Supergene clays are concentrated along faults, dike margins, and within rocks containing carbonate. Gold mineralization is not associated with supergene clay minerals within the Genesis and Blue Star deposits.Rocks classified as silicic-argillic in the Popovich Formation represent the most significant gold host. Silicic-argillic rocks commonly exhibit bedding-parallel alteration zones. This pattern of alteration indicates that stratigraphy as well as northwest-trending structures played a significant role in the migration of gold-bearing fluids. Based on K-Ar age determinations of hydrothermal 1M illite associated with gold, the main event of mineralization in the Genesis and Blue Star deposits occurred between 93 and 100 Ma, during mid-Cretaceous time.

The hexactinellid spongeCyathophycusfrom the Lower-Middle Ordovician Vinini Formation of central Nevada

The new speciesCyathophycus pseudoreticulatusand a fragment ofCyathophycus reticulatus? Walcott, 1879, are described and reported from the lower part of the Upper Member of the Vinini Formation from black shale of late Whiterockian age. The sponges were collected from the north fork of Vinini Creek, in the north-central part of the Roberts Mountains, Eureka County, Nevada.

Nevada's Little Smoky Valley: A High-Potential Valley in the Paleozoic Fairway

Little Smoky Valley, located in east-central Nevada between Railroad valleys, has been demonstrated to have all of the elements essential for oil production: generating source rock, fracture-porous reservoir rock, tight top and lateral seals as the trapping mechanism, and closed structure. The valley lies in the heart of a mature Chainman (Mississippian) oil-generating fairway, which is coincident with the western part of the Antler foreland basin, and runs from Pine Valley in the north to Railroad Valley in the south. A southeastern Little Smoky Valley prospect, at the point where Eureka, White Pine, and Nye counties converge, was defined by using a combination of geological, geochemical, and geophysical methods, as well as remote sensing. There was 880 ft of shows in the first of two stagecoach wells, which is now interpreted to be just below the oil-water contact within the freshwater drive zone of the carrier beds. Minor Sevier hinterland overthrusting was demonstrated to have occurred in this mostly extensional province. The immediate subthrust in the first Stagecoach well contains palynomorphs dated as earliest Tertiary, and a syntectonic conglomerate exists at the very lip of the thrust just 1500 ft to the east. Thus, neither Antier (Roberts Mountains) thrusting normore » post-Sevier low-angle normal detachment faulting is indicated. Although Sevier thrusting does exist, the west-east offset is minor.« less

Resumed Water Use Cures Forfeiture

In July 1989, Eureka County in Nevada transferred water rights to the town of Eureka to augment the latter's decline in the yield of water. The town also had applied for a change in the point of diversion to use another well, which was less degraded. Two county residents protested, claiming the town had forfeited the purchased water rights by failure to use for five consecutive years, 1983‐1988. The state engineer held a hearing and concluded that 440 acre‐feet of water had been forfeited because of nonuse. The town appealed. The trial court ruled against the town, finding that the state forfeiture‐and‐abandonment law was constitutional and could be applied retroactively. The appeallate court agreed the forfeiture statute was constitutional; however, it reversed the trial court because the town's resumption of substantial use cured the forfeiture.

Petroleum Potential of Antelope Valley, Eureka County, Nevada

Petroleum Potential of Antelope Valley, Eureka County, Nevada

New hexactinellids from the Siluro-Devonian of the Snake Mountains, Elko County, Nevada, and a new locality forGabelia

New specimens ofGabelia pedunculusRigby and Murphy, 1983, and of the new speciesGabelia gigantaandGabelia fasciculaare described from the Siluro-Devonian(?) Roberts Mountains Formation from Loomis Creek Canyon in the Snake Mountains, northeastern Elko County, Nevada. Stalk fragments ofG. pedunculusare similar to the holotype from the northern Roberts Mountains, Eureka County, Nevada.Gabelia gigantan. sp. is a large species with skeletal elements in the stalk twice the size of elements inG. pedunculus. Gabelia fasciculan. sp. is based on thick-walled, cup-like upper parts where a gastral layer of coarse, diagonally oriented spicules contrasts to a dermal layer of regular vertical and horizontal bundles of hexactine-based spicules of at least two orders around parietal gaps. The specimens are all part of a probably transported seafloor assemblage.