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Abstract-Ground penetrating radar (GPR) has become a popular geophysical tool for locating subsurface karst features such as cavities, conduits and solutionally enlarged fractures. This study examines the usefulness of GPR [...]

Intrafragment ecology is little studied for imperiled riverine fishes although river fragmentation and habitat loss increasingly threaten sensitive species. A long-term population-monitoring program in the Pecos River, New Mexico, provided detailed data for 15 annual cohorts of speckled chub (Macrhybopsis aestivalis), which were used to assess intrafragment patterns in recruitment and year-class strength in relation to distributional patterns, flow-regime characteristics, and air temperature. Cohorts avoided a degraded upstream reach. Age-1 and older individuals had distributions consistently centered within a central, relict-ecosystem reach that contained high-quality habitat. Age-0 individuals were widespread within the relict- ecosystem reach and a channelized reach downstream. Distributional patterns suggested that some individuals that recruited in the channelized reach dispersed upstream into relict-ecosystem habitat thereafter. One cohort always numerically dominated the population because cohorts never lived beyond 2 years. Recruitment was density-independent and predicted year-class strength. No aspect of the flow regime explained variation in recruitment. Year-class strength was consistent among cohorts because of densitydependent mortality. High-quality habitat in a centralized location, potential for dispersal between channelized and relictecosystem reaches, and diffuse distribution of pelagic-broadcast propagules throughout both reaches combined to facilitate successful annual recruitment and population persistence. L'ecologie intrafragment des poissons fluviaux en peril est peu etudiee, meme si la fragmentation des cours d'eau et la perte d'habitats menacent de plus en plus les especes sensibles. Un programme de surveillance a long terme des populations dans la riviere Pecos, au Nouveau-Mexique, a fourni des donnees detaillees sur 15 cohortes annuelles du cyprinide Macrhybopsis aestivalis, qui ont ete utilisees pour evaluer les motifs intrafragment du recrutement et de la force des classes d'age par rapport aux motifs de repartition, aux caracteristiques du regime d'ecoulement et a la temperature de l'air. Les cohortes evitaient un troncon amont degrade. Les individus d'un an et plus presentaient des repartitions uniformement centrees dans un troncon d'ecosysteme relique central renfermant des habitats de bonne qualite. Les individus de moins d'un an etaient repandus dans le troncon d'ecosysteme relique, ainsi que dans un troncon canalise situe en aval. Les motifs de repartition donnaient a penser que certains individus recrutes dans le troncon canalise se dispersaient par la suite vers l'amont dans l'habitat de l'ecosysteme relique. Il y avait toujours une cohorte dominante dans la population sur le plan du nombre puisque les cohortes ne vivaient jamais plus de 2 ans. Le recrutement etait independant de la densite et predisait la force des classes d'age. Aucun aspect du regime d'ecoulement n'expliquait les variations du recrutement. La force des classes d'age etait uniforme d'une cohorte a l'autre du au fait que la mortalite dependait de la densite. Combines, des habitats de bonne qualite dans un lieu centralise, le potentiel de dispersion entre les troncons canalise et d'ecosysteme relique et la repartition diffuse de propagules a dispersion pelagique dans les deux troncons facilitaient un recrutement annuel efficace et la persistance de la population. [Traduit par la Redaction], Introduction River fragmentation, altered streamflow regimes, and habitat loss threaten riverine fishes (Zwick 1992; Mims and Olden 2013; Hoagstrom 2015). Identification of critical habitat features is necessary to conserve imperiled [...]

New U-Pb zircon ages, geochemistry, and Nd isotopic data are presented from three localities in the Paleoproterozoic Mazatzal province of southern New Mexico, United States. These data help in understanding the source regions and tectonic setting of magmatism from 1680 to 1620 Ma, the timing of the Mazatzal orogeny, the nature of postorogenic magmatism, Proterozoic plate tectonics, and provide a link between Mazatzal subblocks in Arizona and northern New Mexico. The data indicate a period from 1680 to 1650 Ma in which juvenile felsic granitoids were formed, and a later event between 1646 and 1633 Ma, when these rocks were deformed together with sedimentary rocks. No evidence of pre-1680 Ma rocks or inherited zircons was observed. The igneous rocks have [[epsilon].sub.Nd](t) from -1.2 to +4.3 with most between +2 and +4, suggesting a mantle source or derivation from similar-aged crust. Nd isotope and trace element concentrations are consistent with models for typical arc magmatism. Detrital zircon ages from metasedimentary rocks indicate that sedimentation occurred until at least 1646 Ma. Both local and Yavapai province sources contributed to the detritus. All of the samples older than ca. 1650 Ma are deformed, whereas undeformed porphyroblasts were found in the contact aureole of a previously dated 1633 Ma gabbro. Regionally, the Mazatzal orogeny occurred mainly between 1654 and 1643 Ma, during final accretion of a series of island arcs and intervening basins that may have amalgamated offshore. Rhyolite magmatism in the southern Mazatzal province was coeval with gabbro intrusions at 1633 Ma and this bimodal magmatism may have been related to extensional processes following arc accretion. Keywords: Mazatzal province, New Mexico, Proterozoic, U-Pb geochronology, zircons, neodymium.

We studied the alluvial histories of eight small ( Keywords: alluvial stratigraphy, valley fills, Younger Dryas, Holocene, millennial scale, climate change, southwestern United States, High Plains. doi: 10.1130/B26034.1

Bomburia and Ellipsodon are poorly known taxa from the early Paleocene of western North America. New fossil material from New Mexico expands morphological information and allows taxonomic revision of these taxa. Bomburia is a valid genus, whereas Platymastus palantir, previously considered to be a loxolophine arctocyonid, is probably a junior synonym of B. prisca and as such reveals the upper molar morphology of this taxon. Ellipsodon is highly derived relative to other mioclaenid condylarths. It has a reduced mesial dentition, with the probable loss of the Pl/pl. P2-3/p2-3 are reduced and show a simple incisor-like morphology. Ml/ml and especially M2/m2 are simple with highly inflated protocones/protoconid-metaconids accentuating a mortar-and-pestle-like chewing function. The M3/m3 are more reduced than in any other mioclaenid. Mioclaenidae is monophyletic and endemic to western North America. There is no support for a close relationship between Mioclaenidae and South American or African ungulates.

ABSTRACT--Distributional records and natural history information are presented for uncommon mammals on the Llano Estacado in eastern New Mexico. The specific localities of record represent the first on the Llano [...]

The impact of faults on fluid flow and transport through thick vadose zones depends in part on the nature of fault-zone deformation. Both fractures and deformation bands occur in ignimbrite sequences at Los Alamos, New Mexico, and Busted Butte, Nevada. The primary controls on mode of failure are grain-contact area and strength, which are directly related to degree of welding and crystallization and inversely proportional to porosity. Low-porosity welded units deform by transgranular fracture; high-porosity, glassy, nonwelded units deform by cataclasis within deformation bands. Moderately high porosity, nonwelded units that have undergone devitrification and/or vapor-phase crystallization form either deformation bands or fractures, depending on local variations in the degree and nature of crystallization. Grain- and pore-size reduction in deformation bands commonly produces indurated, tabular zones of clay-sized fault material. Many of these bands are locally rich in smectite and/or cemented by carbonate. Preferential wetting of deformation bands is inferred to promote alteration and cementation. We therefore interpret variably altered fault-zone material as evidence of preferential fluid flow in the vadose zone, which we infer to result from enhanced unsaturated permeability due to pore-size reduction in deformation bands.

We report, for the first time, high-precision Pb isotope data from a high-silica rhyolite. Prior work on Sr isotopes in the 1.6 Ma Otowi Member of the Bandelier Tuff (Valles caldera, New Mexico) established that large [sup.87]Sr/[sup.86]Sr variations exist among Otowi glasses and sanidine phenocrysts. While the glasses display unequivocal evidence for wall-rock contamination of the Otowi magma following sanidine growth, a positive correlation between [sup.87]Sr/[sup.86][Sr.sub.i] and [sup.87]Rb/[sup.86]Sr among the feldspars could be interpreted as either a mixing line or an in situ magmatic isochron dating a differentiation event ~270 k.y. prior to eruption. The [sup.206]Pb/[sup.204]Pb and [sup.87]Sr/[sup.86]Sr ranges for Otowi sanidines are 17.790 [+or-] 0.002 to 17.831 [+ or -] 0.002 and 0.7074-0.7052, respectively. This Pb isotope range cannot be produced by radiogenic ingrowth at the U/Pb ratios of the host magma on any geologically reasonable time scale, and hence is unequivocal evidence for open-system behavior of the Otowi magma prior to and/or concurrent with feldspar growth. Open-system behavior is predicted to control Sr isotope variations due to much higher concentrations of Sr, relative to Pb, in the country rock than in the magma. These observations therefore undermine any age significance of the Rb-Sr isotope variations. In the absence of supporting data, Rb-Sr relations alone do not impart any information about residence times of high-silica rhyolite magmas with subchondritic concentrations of Sr. Keywords: high-silica rhyolite, magma chambers, Sr isotopes, Pb isotopes, crustal contamination.

Recent excavations and reanalysis of existing data on communal pit structures provide intriguing insights into ritual and cultural developments over a period of about 350 years, from A.D. 800 to 1140, in the Mimbres Valley of southwestern New Mexico. In the middle of this period, people shifted dwellings from pithouses to pueblos, a shift previously viewed as the pivotal transformation of Mimbres society. In this paper we show that significant changes in Mimbres society began in the A.D. 800s. Trends in the construction methods of communal pit structures, the placement of dedicatory items within them, their ritual retirements, and their long-lived significance within Mimbres villages, reflect other changes that occurred in Mimbres society. We contend that in the A.D. 800s, rapid change based on strong connections with the Hohokam of southern Arizona and agricultural intensification began a trajectory that culminated in the Classic Mimbres pueblos of the A.D. 1000s and early 1100s., In most parts of the American Southwest, public architecture has long been an important focus of archaeological research and has figured prominently in reconstructions of social, ritual, and political organization. [...]

Three new species of Viverravidae (Carnivora: Miacoidea) are described: Protictis simpsoni, P. minor, and Bryanictis paulus. Holotypes and referred specimens are from the Angel Peak area, Kutz Canyon, San Juan Basin, New Mexico and are of middle Torrejonian age (middle Paleocene). The holotype of Protictis simpsoni includes a skull--the oldest known skull of the Order Carnivora. The locality is narrowly restricted stratigraphically and geographically, and specimens are better preserved than most other viverravid specimens of San Juan Basin strata.

The Lower Permian (Late Wolfcampian) marginal marine facies of the Robledo Mountains Member (Hueco Formation) of the Robledo Mountains, New Mexico, contains a diverse ichnofauna dominated by vertebrate trackways. Four new arthropod ichnotaxa are described. Tonganoxichnus robledoensis new ichnospecies, consists of repeated small traces comprising imprints of anteriorly directed legs, an elongate tapering abdomen, and a thin tail. Hedriumichnus apacheensis new ichnogenus and ichnospecies consists of isolated small traces comprising imprints of laterally-directed legs, a broad tapering abdomen, and a short tail. Rotterodichnium major new ichnospecies is a large trace with imprints of the head and thorax, a long thin abdomen and three pairs of legs, increasing in length posteriorly. Quadrispinichna parvia new ichnogenus and ichnospecies consists of four diverging or sub-parallel linear or curvilinear imprints of approximately equal length. Tonganoxichnus, previously known from the Upper Carboniferous of eastern Kansas, is interpreted as produced by a jumping monuran (an extinct group of wingless insects). Hedriumichnus, known only from the Robledo Mountains, is interpreted as the resting trace of a nymph of a primitive Ephemeroptera or Plecoptera. Rotterodichnium, previously known from the Lower Permian of Germany, is interpreted as the resting trace of a large dragonfly-like form (Protodonata, Odonata, or Megasecoptera). Quadrispinichna, previously recorded but not named, from the Lower Permian Ecca succession of South Africa, is interpreted as a resting trace of a crustacean. These rare traces increase our understanding of the diversity and behavior of nonmarine arthropod communities in the Lower Permian.

Stable isotope compositions of brachiopod shells from the Alamogordo Member of the Lake Valley Formation (south-central New Mexico) provide information about Early Mississippian paleoclimate. The Alamogordo Member was deposited on a ramp at the southwestern edge of the North American craton, at lat 20[degrees]S. It consists of cherty lime-mudstone to lime-packstone (predominantly mudstone and wackestone) strata and scattered mud-cement (Waulsortian) mounds. The brachiopods analyzed lived at water depths estimated to have been between 100 and 300 m. The [[delta].sup.18]O values of well-preserved shells of a single species of brachiopod average -2.3% relative to PDB (the Peedee belemnite isotope standard). This average represents a temperature of 21-26[degrees]C if the isotopic composition of the seawater ([[delta].sup.18][O.sub.sw]) was between 0% and -1%, as inferred from Pleistocene and Holocene [[delta].sup.18][O.sub.sw] and other considerations. Sea-surface temperature would have been 26-31[degrees]C (after we applied a +5 [degrees]C correction for water depth). This tropical climate for an Early Mississippian low-latitude site agrees with previous isotopic and climate-modeling results, but contrasts with a temperate climate inferred from comparison of the lithology and biota of the Alamogordo Member with those of modern temperate carbonates. Keywords: Early Mississippian, New Mexico, oxygen isotopes, paleoclimate.

Research is presented on habitat selection and roosting behavior by Brown-headed Cowbirds, an avian brood parasite, to enhance wildlife management strategies aimed at protecting threatened species. Roosting sites include riparian woodland, conifer forest, and open-prairie cattail marshes, which expand the range of territory Cowbirds are able to cover.

Sharp-shinned and Cooper's Hawks exhibit differential migration timing during fall in New Mexico and Nevada, but the order in which they migrate differs from some noted theories of differential migration, such as body size and social dominance. A new study shows a sex-specific differential migration timing in the two species, the order being: juvenile females, juvenile males, adult females and adult males, It is suggested that the age-related differences may be explained by foraging efficiency and that rate of travel may explain sex-related differences.

Pinyon-juniper woodlands are among the least studied livestock grazing habitats, despite their dominance in the western US where they occupy more than 85 million ha. Almost nothing is known about the interaction between grazing and the birds that occupy such systems. A new study compares the community composition and nesting success of songbirds within actively grazed pinyon-juniper woodlands with similar woodlands where livestock has been excluded. Parasitism by the brown-headed cowbird, often associated with livestock, is seen to be an important constraint on the nesting activity of some birds.

Lower Mississippian carbonate mud-rich bioherms, generally referred to as Waulsortian mounds, are commonly associated with low-paleolatitude carbonate ramp settings and have recently been recognized as important hydrocarbon reservoirs. The factors controlling localization of Waulsortian mounds have heretofore been poorly understood. Stratal relations exposed in the Alamogordo Member of the Lake Valley Formation in the Sacramento Mountains of New Mexico illustrate the effects of tectonism on carbonate sedimentation prior to, during, and after mound growth. They indicate that mound initiation and localization were strongly controlled by tectonically generated, intraramp, sea-floor topography. These observations bear strongly on understanding the controls on localization and growth of mud mounds in general. Stratal geometries observed in the underlying Andrecito Member indicate that this topography was modified by erosional and depositional processes prior to mound initiation. Mounds formed on the surfaces and margins of the intraramp topography as the result of aggradational, in situ accumulation of biogenic sediment. Differences in growth geometry of stratal units within individual mounds and differences between mounds are correlated with position of the mound on the ramp and the deformation occurring immediately prior to mound growth. It is probable that local tectonism continued during mound growth, and that local differences in the amount of relative uplift resulted in different amounts of space for growth of individual mounds, and thus determined differences in mound size and geometry.

The kinematic and erosional history of the Rio Grande uplift, a large northwest-trending, basement-involved, thrust-bounded, block uplift of Laramide age (latest Cretaceons-early Tertiary) in south-central New Mexico, is documented by elastic rocks that accumulated in the complementary Love Ranch basin. The synorogenic to postorogenic McRae and Love Ranch Formations are as much as 1460 m thick: they filled the Love Ranch basin and onlapped the Rio Grande uplift. Present outcrops of the two formations cover an area of 100 [km.sup.2] and reveal the stratigraphic architecture of the basin fill in three dimensions. Lithofacies distribution, clast size and composition, paleoflow data, syndepositional structures, nature of the basal unconformities, and ages of basin fill provide essential data for constraining uplift history. Laramide shortening began between Campanian and latest Maastrichtian time, and initially created open, symmetrical, northwest-trending folds, as well as a broad, approximately symmetrical uplift. This incipient Rio Grande uplift was capped by Upper Cretaceous volcanic rocks of intermediate and silicic composition, which were the primary source of volcanic detritus in the latest Cretaceous-Paleocene(?) McRae Formation. At this stage of uplift, the northeastern flank dipped gently northeastward away from the crest and served largely as a sediment transport surface; McRae strata accumulated only on distal parts of the surface in an embryonic Lure Ranch basin to the northeast. Following an interruption in tectonism lasting as much as 10 m.y., renewed shortening in Paleocene(?) time elevated the Rio Grande uplift and formed the Love Ranch basin. At least 900 m of upward-fining, elastic Love Ranch strata of Paleocene-Eocene age accumulated in the basin. The Love Ranch lithofacies record a gradual southwestward shift of alluvial-fan depocenters, which resulted from growth of basin-margin structures and increasing basin asymmetry. Syndepositional synclines and angular unconformities record the growth of both intrabasinal folds and basin-margin thrusts. Clast compositions document progressive erosional unroofing of the Rio Grande uplift from Upper Cretaceous volcanic rocks into Precamhrian granite anti metamorphic rocks. Canyons 0.4 km deep locally drained the uplift, and maximum topographic relief may have approached 2 km. By late Eocene time, Love Ranch piedmont-slope deposits onlapped the uplift, burying all hut the higher granite peaks. At this stage, the Love Ranch basin broadened and was the site of broad alluvial plains crossed by braided rivers draining to saline lakes. Our analysis of syntectonic sedimentary rocks in the Love Ranch basin supports recent models of evolution of Laramide basement-involved block uplifts in which early stages produce approximately symmetrical structures, and sediment derived from the uplift is transported across must of the uplift flank to he deposited in a distal selling. At this stage the future footwall of uplift-boundary faults dips basin-ward in a ramp-like fashion, providing a sediment transport surface. As boundary thrust faults and fault-propagation folds evolve and grow basin asymmetry rapidly develops, causing depocenters to shift toward footwall positions near the overthrust margins. This evolution from symmetrical to asymmetrical structures is reflected in an overall upward-fining sequence in the basin fill.

We studied the short-term effects of experimental flooding on a population of Peromyscus leucopus in a Rio Grande riparian forest that had not flooded for over 50 y. We monitored populations at two sites for 2 yr before flooding and then for 3 yr during which we flooded one site between mid-May and mid-June each year. Considerable interannual variation in density, was detected at both sites, with no clear effect of flooding on density. Some mice stayed within the forest during flooding and used trees as refugia. Survivorship decreased slightly at the flood site after the first flood but did not differ from the reference site 2 mo after flooding that year, nor in the final year. There was no difference between sites in recruitment of new individuals., INTRODUCTION Disturbance plays an integral role in establishing and maintaining southwestern riparian ecosystems, and flooding is the most common natural disturbance in these systems (Szaro, 1991). Although large river floodplains [...]

Regional, eastward trending piercing lines defined by stratigraphic truncations and depositional pinchouts in Jurassic and Cretaceous strata in north-central New Mexico allow 5 to 20 km of right slip between the eastern margin of the Colorado Plateau and the craton to the east in Laramide (Late Cretaceous-Paleogene) and younger time. Estimates of 60-170 km of Laramide right slip by previous workers were based largely on (1) the amount of presumed crustal shortening across thrust and reverse faults in the Wyoming province north of the plateau or (2) offset of piercing lines defined by a Proterozoic, regionally subhorizontal, isobaric metamorphic surface that intersects preexisting structures and steep stratigraphic contacts. Major right slip inferred on the basis of these metamorphically defined piercing lines in Proterozoic rocks must therefore predate the Laramide orogeny and cannot be used to support a model postulating large-scale Laramide right slip. Restoration of 60-170 km of right slip creates lateral offset of the north-south extent of the Jurassic Todilto Formation, producing an untenable paleo-depositional basin geometry.

We examined the significance of arroyo-riparian habitat to birds in the Chihuahuan Desert of south-central New Mexico. Nests (N = 620) of 27 species were monitored during 1993-1995. Twenty-three species nested in arroyos and 20 species nested in uplands. Northern Mockingbirds (Mimus polyglottos), Rock Wrens (Salpinctes obsoletus), and Verdins (Auriparus flaviceps) nested most frequently in arroyos. Black-throated Sparrows (Amphispiza bilineata), Northern Mockingbirds, and Scott's Orioles (Icterus parisorum) nested most frequently in uplands. Nest density in arroyos was more than twice that of uplands (0.64 nests/ha versus 0.27 nests/ha). Nest success and predation rates did not differ between arroyos and uplands for Black-throated Sparrows, Northern Mockingbirds, and Crissal Thrashers (Toxostoma crissale). Nest predation was the primary cause of mortality to eggs and nestlings in both habitats. Torrey yucca (Yucca torreyi), javelina bush (Condalia warnockii), and little-leaf sumac (Rhus microphylla) were the most frequently used nest substrates, even though these shrubs were among the lowest in density. Maintaining this habitat and protecting sparse shrub species used as nest substrates may have long term importance in managing Chihuahuan Desert bird communities., Populations of some Neotropical migrants have declined over the last 20-30 years (Finch 1991). A significant reason for these declines is thought to be caused by loss of habitat on [...]

Cirsium vinaceum (Asteraceae), an endemic thistle of the Sacramento Mountains, New Mexico, is federally listed as threatened. It occurs in spring and streamside habitats; individual patches of plants vary widely in size and in distance from one another. We used floating seed traps to determine if seed movement by water contributes to gene flow and migration between patches. Seeds move in substantial numbers for considerable distances along these streams, indicating that a biological definition of population for this species must encompass more than single patches. We discuss implications for management, including the potential for restoration or recovery via aquatic dispersal., INTRODUCTION Seed dispersal is a primary determinant of gene flow among plant populations. Interpretation of dispersal data is often problematic, sometimes underestimating gene flow because of erroneous assumptions about neighborhood [...]

INTRODUCTION Coyote (Canis latrans) population dynamics are influenced by interactions between their social organization and food availability (Knowlton and Stoddart, 1983; Windberg, 1995) and by the degree of human exploitation [...]

We studied timing, abundance, subspecies composition, fat stores, stopover length, and habitat use of Willow Flycatchers (Empidonax traillii) during spring and fall stopover along the Middle Rio Grande, New Mexico. Spring migration started in mid-May and lasted about a month. Fall migration started in early-August and also lasted about a month. The most abundant subspecies was the Southwestern Willow Flycatcher (E. t. extimus), followed by E. t. brewsteri, E. t. adastus, and E. t. traillii. Nearly half of the Willow Flycatchers captured had no observable fat. Spring flycatchers had more fat stores than fall flycatchers. Willow habitat had the highest capture rate among the habitats sampled. Willow Flycatchers caught in willow habitat had higher fat stores than those caught elsewhere. Recaptured Willow Flycatchers had an average body mass gain of 1.6%/day with a short stopover length. Most Willow Flycatchers were unable to reach their destinations in a single flight, making it necessary for them to replenish their energy stores elsewhere en route. We suggest that the riparian woodlands of the middle Rio Grande provide important refueling sites for stopover flycatchers as they migrate between their breeding and wintering grounds., The Willow Flycatcher (Empidonax traillii) breeds extensively from southern British Columbia east to Maine and south to California, Arkansas, and Virginia. It winters in Middle America from Veracruz and Oaxaca [...]

Recently collected specimens of Catopsalis fissidens from the Torrejonian interval of the Nacimiento Formation in the San Juan Basin, New Mexico significantly augment knowledge of the morphology and dental variability of the species. This new knowledge suggests C. foliatus Cope, 1882 (=C. johnstoni Fox, 1989) is a valid Puercan species and that C. fissidens Cope, 1884a is a subjective senior synonym of C. utahensis Gazin, 1939. This latter synonymy further increases taxa shared between the Dragon Canyon local fauna of Utah and the Torrejonian fauna of the San Juan Basin, thus supporting previous inclusion of the Dragonian land-mammal 'age' in the Torrejonian.

Observations made in 1987 with the NCAR King Air aircraft and in 1993 with the New Mexico Institute of Mining and Technology dual-polarization radar have revealed the presence of supercooled raindrops in some New Mexico summertime cumulus clouds. In the case of the radar data, the evidence for the supercooled drops came from a column of enhanced [Z.sub.DR] that extended well above the 0 [degrees] C level. The in situ data indicated that the supercooled raindrops were observed when cloud base was warmer than about 7 [degrees] C and the depth of the cloud was greater than about 2.5 km.

The Rio Puerco volcanic necks and Mesa Prieta, located in the transition zone between the Rio Grande rift and southeastern Colorado Plateau, New Mexico, are part of the larger Mount Taylor volcanic field. The comparatively small volume, but numerous, eruptions represented by the volcanic necks provide geochronologic insight to the larger magmatic system at Mount Taylor and in a broader sense to regional late Cenozoic volcanism of the southeastern Colorado Plateau transition zone. Whole-rock 40Ar/39Ar ages from 17 basaltic plugs, flows, and dikes range in age from 4.49 to 2.05 Ma and overlap the 3.73 to 1.57 Ma volcanism observed at Mount Taylor. Volcanic eruptions in the Rio Puerco Valley were few and sporadic prior to 3.17 Ma; after this time, eruptions progressively increased to a zenith at ca. 2.70 Ma and ceased altogether after 2.56 Ma. Volcanism at Mesa Prieta (2.36-2.05 Ma) is significantly younger than that recognized for the volcanic necks and is considerably more voluminous and chemically evolved. Paleomagnetic data from the volcanic necks show that basalts carry reliable thermoremanent magnetizations; 9 of 13 sites exhibit well-grouped statistical characteristics. Polarity results provide an independent check of the 40Ar/39Ar analytical accuracy and are useful in resolving problems associated with excess Ar and/or Ar loss. The magmatic evolution of the Rio Puerco necks differs from the rest of the Mount Taylor volcanic field in duration of volcanism, erupted volume, and composition. These differences are believed to be related to the nonuniform character of the lithosphere's structure and dynamic thermal construct across the Jemez zone in the vicinity of the Mount Taylor volcanic field. Our model proposes a zone of localized high heat flow and higher magma production beneath Mount Taylor volcano from 3.73 to 1.57 Ma to produce a suite of voluminous basalt-rhyolite compositions. However, east of Mount Taylor in the Rio Puerco Valley where the lithosphere is proposed to be cooler and more rigid throughout the same time interval, small-volume, xenolith-bearing, mafic eruptions are more typical. A cooler lithosphere is consistent with both low magma production rates and the observed small-volume eruptions of the Rio Puerco necks. A preexisting structural trend in the Rio Puerco Valley is believed to have assisted the ascent of volatile-rich, Rio Puerco magmas, particularly through the upper crust.

Livestock in dry regions tend to graze close to riparian areas and other habitats where water, shade and tasty vegetation is commonly available. These areas are also important to wildlife and the effects of livestock grazing is of concern to wildlife managers. Details of a 10-year study designed to show the effect of livestock grazing on small mammals and vegetation at a desert wetland in southwestern Mexico are presented. Results show that there were consistently more small mammals on the plots from which livestock was excluded, reflected by comparable differences in vegetation.

The Cerro Toledo Rhyolite comprises a group of domes and tephra which were erupted during the interval between two caldera-forming ignimbrites, the Tshirege Member and Otowi Member of the Bandelier Tuff, in the Jemez Volcanic Field, New Mexico. To provide a chronologic framework for geochemical and isotopic studies on these rhyolites, which record the evolution of the Bandelier magma system during this interval, a 40Ar/39Ar geochronology study was undertaken. Pumice from major pyroclastic fall deposits within the rhyolite tephra and samples from the rhyolite domes were dated as well as the stratigraphically bracketing Bandelier Tuff. Analyzed crystal populations range from being fairly homogeneous juvenile material to very heterogeneous mixed juvenile and xenocrystic assemblages. In most cases dominant groups of juvenile sanidine crystals define 40Ar/39Ar ages which agree with stratigraphic constraints. Plagioclase analyses are distinctly more scattered and do not typically define reasonable ages. The 40Ar/39Ar ages for the two members of the Bandelier Tuff yield an interval of 380 [+ or -] 20 k.y. between these caldera-forming eruptions. During this interval nine major pyroclastic pumice units were deposited in the sections studied, for which six yield isochron ages, one a weighted mean age, one a maximum age, and one no reliable age due to lack of sanidine. 40Ar/39Ar dates on pumice fall units within the Cerro Toledo Rhyolite tephra indicate that eruptive activity occurred at >1.59, 1.54, 1.48, 1.37 and 1.22 Ma. 40Ar/39Ar dating of Cerro Toledo Rhyolite domes indicates these were erupted within the caldera at 1.54, 1.45, 1.38-1.34, and 1.27 Ma. The dates obtained indicate that eruptive activity occurred throughout the 380 k.y. interval between the two members of the Bandelier Tuff, but suggest that eruptions producing both tephra and domes occurred during discrete intervals at ca. 1.54, 1.48, and 1.38-1.34 Ma. The interval from 1.34 to 1.38 Ma was particularly active; 7 of 18 units dated are these ages.

Massive slump complexes composed of Pliocene basaltic rocks and underlying Miocene and Pliocene sediments flank the Rio Grande along 16 km of northern White Rock Canyon, New Mexico. The toe area of at least one slump complex was active in the late Pleistocene, damming the Rio Grande at least four times during the period from 18 to 12 14C ka and impounding lakes that extended 10-20 km upriver. Stratigraphic relationships and radiocarbon age constraints indicate that three separate lakes formed between 13.7 and 12.4 14C ka. The age and dimensions of the ca. 12.4 ka lake are best constrained; it had an estimated maximum depth of [approximately equal to]30 m, a length of [approximately equal to]13 km, a surface area of [approximately equal to]2.7 [km.sup.2], and an initial volume of [approximately equal to]2.5 x [10.sup.7] [m.sup.3]. The landslide dam responsible for this lake was apparently stable, and the lake filled completely with laminated silt-rich lacustrine sediment and overlying coarse sands and gravels that represent bed load of the Rio Grande. A lake that formed at [less than or equal to]17.5 ka was [approximately equal to]21 km long and apparently failed catastrophically, recorded by probable outburst flood deposits that extend downriver from the landslide dam. An older ([greater than or equal to]43 14C ka) landslide-dammed lake is less well constrained, but it had a maximum depth of at least 57 m, an estimated minimum length of 25 km, and a surface area of 25 [km.sup.2]. Deposition of coarse sands and gravels of the Rio Grande over lacustrine sediments indicates that the landslide dam responsible for this older lake also was stable; extrapolation of historic Rio Grande sediment yield data suggests that this lake persisted for 100-1000 yr. The stability of the dam may have been due to armoring of the outflow channel with basalt boulders. The youngest landslide-dammed lakes formed during a period of significantly wetter regional climate, strongly suggesting that climate changes were responsible for reactivation of the slump complexes. We are not certain about the exact triggering mechanisms for these landslides, but they probably involved removal of lateral support due to erosion of the slope base by the Rio Grande during periods of exceptionally high flood discharge or rapid incision; increased pore pressures associated with higher water tables; higher seepage forces at sites of ground-water discharge; or some combination of these processes. Seismic shaking could also have contributed to triggering of some of the landslides, particularly if aided by wet antecedent conditions.

Heat-flow values calculated along a profile in southeast New Mexico are used to study the regional ground-water flow pattern. The west-east profile extends from the Sacramento Mountains, across the southern part of the Roswell artesian basin, to the New Mexico-Texas border. The heat-flow data are generally calculated from bottom-hole temperatures estimated at various depths, and are therefore thought to reflect depth-dependent anomalies (principally ground-water flow). Two major positive heat-flow anomalies, interpreted to indicate upward ground-water flow, are present along the profile. A narrow anomaly in the western part of the profile is consistent with upward ground-water movement along the western boundary of a buried Precambrian horst. A rather broad anomaly in the middle of the profile appears to be associated with cross-formational flow and discharge to the Pecos River. Both anomalies may be associated with upward flow from depths of 915 or 1220 m and possibly 1524 m in the western region, but probably not deeper than 1829 m. Vertical ground-water flow appears to be absent just east of the Mescalero Ridge; farther east on the High Plains, the data are generally consistent with downward ground-water flow at depths of 610-1220 or 1524 m.

Well-dated lacustrine deposits in northern White Rock Canyon, New Mexico, record damming of the Rio Grande by at least four separate failures of a slump complex between about 17.5 and 12.4 ka (14C), linking mass movements to a period of rapid climate change in the western United States. Failure of metastable slumps probably resulted from removal of lateral support during down-cutting and erosion by the Rio Grande and from a decrease in resisting forces due to increased pore pressures. Our chronology suggests that the lake that formed between 17.5 and 15.0 ka may record effects of both glacial melt and pluvial activity (mainly enhanced rainfall); the youngest lake ([approximately]12.4 ka) may record pluvial runoff; and the intermediate lakes (13.7 to 13.1 ka) may record pluvial and minor melt-water activity. We have not found lacustrine deposits younger than about 12.4 ka. The record of geomorphic response along the Rio Grande suggests that late Pleistocene climatic changes may have triggered similar mass movements elsewhere in the Southwest.

The [approximately equal to]300 [km.sup.3], 28.8 Ma granitic Capitan pluton, located in southeastern New Mexico, was the source of high-temperature (up to 600 [degrees] C), high-salinity (up to 80 wt%) fluids that formed small REE-bearing zones of mineralization in the pluton carapace. Erosional dissection of the pluton reveals zones in the granite that are characterized by bubble-like void spaces and fissures. These could be interpreted, on one hand, as original magmatic porosity resulting from the interconnection and/or coalescence of bubbles of magmatic volatile phase, or on the other hand, as void spaces resulting from postcrystallization dissolution. These porous zones grade upward into the brecciated portions of the pluton carapace that hosts mineralization. The zones are planar features, traceable across valleys, and even between adjacent valleys on the pluton's flanks. The orientation of the zones is roughly concentric with the exposed shape of the pluton. Chemical analyses of samples collected across a porous zone reveal that some elements, including Fe, Al, Rb, and Sr are depleted in the entire area surrounding the porous zone, whereas Si, Na, Ba, and Ta are enriched. Other elements, including K, Sb, Zn, Zr, a number of rare earth elements (REE), Pb, and Th, exhibit a slight to strong depletion surrounding the porous zone and a strong enrichment roughly centered on the zone itself. Abundance of high-salinity fluid inclusions in igneous quartz is high within the entire 2.5-m-wide zone but is significantly higher in the central porous zone. The chemical and fluid inclusion abundance patterns could be produced by a two-step process with the wide depletion caused first, by fractionation of elements from the melt into a volatile phase at the time that volatile exsolution first occurred. This could be followed by the superimposed enrichment pattern for certain elements caused by deposition of these elements from trace-element-rich fluids, which evolved in a more central, deeper part of the pluton and were transported along the same zone (although now more crystallized) of fluid migration established earlier, depositing minerals as it cooled. Textural, petrographic, and geochemical evidence suggest that volatiles may have exsolved during crystallization, coalescing into bubble-rich zones that enhance the efficiency of volatile transport.

Since 1978 the results of computational architectural models have been widely used to aid interpretation of ancient alluvial successions: here we present the first quantitative test of such models. We parameterize variables from field and magnetostratigraphic data collected from the well-exposed Pliocene-Pleistocene Camp Rice and Palomas Formations of the Rio Grande rift in south-central New Mexico. Computational runs establish that the LAB (Leeder, Allen, and Bridge) model correctly predicts the gross architectural patterns of ancestral axial Rio Grande half grabens and full grabens. Convergence of tectonic subsidence rate and mean sedimentation rate over the studied interval suggests that the dynamic basis of the models is correct; i.e., it is the tectonic 'draw-down' of axially supplied sediment that controls the net preservation potential of alluvial successions.

New geochronologic data provide evidence for an age of about 50 to 60 ka for the youngest volcanic eruptions within the Valles caldera, New Mexico - an age that is significantly younger than most previous age determinations. Thermoluminescence age estimates for buried soils beneath the El Cajete pumice, a key stratigraphic marker in the region, range from 48 to 61 ka, and 14C analyses of burnt logs within volcanic surge beds near the El Cajete vent yield similar ages of 50 to >58 ka. These data conflict with fission-track, 40 [degrees]/39Ar, and K-Ar ages of 130 to >200 ka, but are supported by recent analyses by electron spin resonance. The results of this study reinforce the need to apply a variety of dating methods when evaluating the age of young volcanic events and support the hypothesis that the El Cajete eruptions were part of a new cycle of volcanic activity in the Valles caldera after an exceptionally long period of quiescence of [approximately to]460 ka. The new age constraints also suggest a previously unrecognized link between cycles of volcanism and pulses of hydrothermal activity in the caldera, such that hydrothermal outflow appears to decrease significantly following completion of eruptive cycles.

In 1992 and 1993, 28 Northern Goshawk (Accipiter gentilis) broods in north-central New Mexico were used in a supplemental-feeding experiment to determine if there was a causal relationship between food availability and survival of young goshawks. We randomly assigned 28 nests as treatments or controls. Every two days (from hatching [late April] until juvenile dispersal [mid-October]) we visited control nest stands and provided food at treatment nest stands. We measured morphological characteristics and attached tarsal-mounted transmitters with mortality switches to 42 nestling Northern Goshawks when they were 21 days old. In both 1992 and 1993, we relocated birds via telemetry every other day until mid-August. We located birds at least once a week from mid-August until mid-October in 1992, and until late-November 1993. There were no significant differences in nestling size. Treatment birds had a significantly higher survival rate during the nestling period in 1993, but not in 1992. Because most control nestlings died from predation, we attribute higher nestling survival to increased time spent in nest stands by adult females, whose presence probably deterred predators.

Fractures in the Bandelier Tuff are potential paths for water movement and transport of contaminants from waste disposal sites and other contaminated areas at Los Alamos National Laboratory, Los Alamos, NM. Contaminants transported in this way could ultimately be found in Los Alamos drinking water or in the Rio Grande, which flows through heavily populated areas in both the USA and Mexico. We conducted this study to determine (i) the morphology and origin of soil-like material in the fractures, and (ii) the likelihood of significant water movement through the fractures. We examined thin sections of fracture fills, soils, and tuffs to obtain fabric and mineralogical data, and collected field data on soil horizons, color, texture, structure, clay films, and root abundance. Fracture fills consist of clay, Ca[CO.sub.3], or combinations of the two with minor inclusions of tuff and sand grains. Clay consists of thick, highly oriented argillans aligned paraliel to fracture walls, and of discrete books in fracture interiors. Carbonate consists ormassive microcrystalline calcite, which completely fills some fractures, and laminae or infillings between clay laminae or books in clay-dominated fractures. The carbonate was precipitated after clay deposition, suggesting a change to a more arid climate. Weaker development of argillans and carbonate features in the soils suggests that the fractures may be derived from older soils that have been stripped by erosion. The presence of live roots throughout the fracture fills indicates the presence of water, but the smectitic clay and massive carbonate make it unlikely that significant water movement is now taking place through the fractures. The potential creation of new macropores by a variety of processes, however, including seismic activity and biologic disturbance, could allow rapid water movement and contaminant transport.

In 1981-1986, we studied Flammulated Owls (Otus flammeolus) nesting in a forest-woodland ecotone at the species' lower elevational limit. Most adults did not renest in the same tree cavity despite previous success. Clutch size was smaller, and eggs were less likely to produce fledglings than in a coniferous forest population studied concurrently by Reynolds and Linkhart (1987b). Additional features of life history and nesting density were similar to other populations, but nesting mass of females and productivity were lower, while density flux was higher. Our study population is marginal ecologically, perhaps limited by food shortage during courtship plus predation and maintained by immigration., The Flammulated Owl (Otus flammeolus) nests in tree cavities in mature coniferous forest, largely in ponderosa pine (Pinus ponderosa) and mixed conifer associations (McCallurn 1994a, b). Its small mass, clutch [...]

Vertical deflection profiles derived from microradian-sensitivity tiltmeter data collected over a 1 yr period suggest that an earth fissure in the subsiding Mimbres Basin is located near the inflection point of an evolving surficial fold of infinitesimal amplitude. Water levels beneath the study site also fell steadily during the period of observation. Calculated curvature profiles, which reflect the sign and relative magnitude of fiber strain along the ground surface, further imply that the fissure was within a zone of contraction throughout the study period. Observed fissure-perpendicular tilts and the location of the fissure at an inflection point rather than along an anticlinal crest are consistent with a mode II fracture (shearing mode crack or fault) rather than a mode I fracture (opening mode crack or joint). Tilting parallel to the fissure further suggests a component of mode III (tearing-mode crack) displacement during the study period. Thus, the three-dimensional displacement, strain, and stress fields around the fissure were considerably more complicated than those suggested by previous fissure monitoring studies and suggest that the fissure may have been formed in compression as a shear crack rather than in tension as an extensional crack. On the basis of the occurrence of right steps in the trace of the fissure, we speculate that our data may reflect contraction across one of the steps as a consequence of left-lateral slip along the fissure.