Horn Mountains Research Articles

Predicting local biological characteristics in streams: a comparison of landscape classifications

Summary1. Landscape classifications group tracts of land based on similar physico‐chemical attributes that may affect the biological characteristics of streams at local scales. We tested the ability of five landscape models to account for variation in algal and macroinvertebrate biomass, brook trout (Salvelinus fontinalis) growth and macroinvertebrate community composition from 132 riffles in 15 catchments in the Big Horn Mountains, Wyoming.2. A model created by the U.S. Forest Service (FS) combined catchment and ecoregion approaches to classify the landscape. Our model used digital elevations to create a landscape classification for streams (DEM). The last three models were based on: (1) standard ecoregions (Ecoregion), (2) the type of underlying bedrock (Geology) and (3) the geographical distance between sites (Site Proximity model).3. Overall, the Ecoregion and Geology models performed better than the two catchment models (FS and DEM) in predicting local biological characteristics. The Geology model was best at predicting differences in algal and macroinvertebrate biomass, the Site Proximity and Ecoregion models were best at predicting patterns of similarity in macroinvertebrate community composition, and the Site Proximity, Ecoregion, Geology, and FS models, in order from best to worst, accounted for significant variation in brook trout growth. The Site Proximity model performed well because of the effects of spatial autocorrelation. The DEM was consistently one of the worst models at predicting local biological characteristics because it failed to include important attributes (e.g. dominant geology). Calcareous geology was positively associated with greater macroinvertebrate biomass and faster brook trout growth, but it was inversely related to algal biomass.4. None of the models accounted for a large amount of variation in local biological characteristics. Single‐scale, landscape classifications may never accurately predict variation in local biological characteristics because: (1) landscapes show a high degree of spatial heterogeneity, (2) local effects are stronger than landscape attributes and (3) there are too many intervening levels between landscape and local scales in the nested hierarchy of streams. However, landscape classifications did account for significant variation in biological characteristics. Thus, they would be a valuable management tool as part of a multi‐scale, hierarchical technique for classifying stream ecosystems.

Integration of mud gas isotope logging (MGIL) with field appraisal at Horn Mountain Field, deepwater Gulf of Mexico

Prior applications of gas isotopic data to reservoir studies have often suggested that measured differences of a few per mil in gases sampled between wells indicated hydrocarbon compartmentalization concomitant with poor reservoir communication. These conclusions were generally invoked without adequate consultation and integration of geological and engineering well data, and only revealed to be true in the simplest of circumstances where pressure data clearly suggested the same. Not surprisingly, gas isotope data has yet to find widespread production engineering applications as a convincing tool for reservoir formation evaluation. This situation is unlikely to change due to the prohibitive drilling economics of acquiring adequate quantities of physical gas samples from down-hole tools in every zone of interest across multiple wells in a field. Recent application of a new technique, mud gas isotope logging (MGIL), has shown comparable isotopic data to traditional gas samples collected from down-hole tools while providing the petroleum systems analyst with the necessary large datasets needed to make accurate and confident reservoir evaluations. Many additional benefits of MGIL to formation evaluation have also been recognized, and it is envisaged MGIL possesses the potential to develop as a standard protocol on drilling wells. This paper documents the first published application of MGIL in the context of complete field-scale reservoir integration and production appraisal encompassing 18 well penetrations over a 3-yr drilling program. Case data from the Horn Mountain Field (Gulf of Mexico) are used to demonstrate this technology and its impact to field assessment and appraisal. Initial well data and two 3-D seismic surveys were used to assess reservoir continuity and compartmentalization across the field. Subtle pressure and gas-to-oil ratio (GOR) differences from eight appraisal wells suggested that the main economic M-Sand may be divided into at least two compartments, however the data could not be unambiguously relied upon in itself. MGIL data provided the strongest evidence in confirming the existence of two ‘baffled’ field compartments. Significantly for subsequent development wells, MGIL data were able to accurately discern and allocate compartments in wells without reliable wireline or absent MDT pressure data. MGIL data also recognized the significance of geological features such as a shale-filled channel visible on amplitude maps, and inferred to serve in concert with faults as a baffled flow barrier. Data such as these may have important implications for reservoir energy and pressure support during production. The impact of hydrocarbon stratification attributed to geological reservoir structural features and/or hydrocarbon phase geochemical density characteristics are also examined. Interpretation of the Horn Mountain MGIL data, in addition to characterizing and verifying oil/gas shows, was also successful in providing essential data on highlighting all penetrated pay zones, deconvolving multiple pure biogenic and mixed biogenic/thermogenic zones, identifying stratigraphic trapping seals and providing detailed petroleum system evaluation.

The Status, Habitat, and Response to Grazing of Water Vole Populations in the Big Horn Mountains of Wyoming, U.S.A.

Microtus richardsoni, the water vole, was listed as a sensitive species in Region 2 of the USDA Forest Service in 1994. Historical records indicate water voles were found in the Big Horn Mountains, but little was known about their current status. The purpose of this study was to locate water voles in the Big Horn Mountains of Wyoming, develop a habitat profile, and evaluate the extent to which livestock grazing affects them. Accessible creeks with habitat requirements for water voles were surveyed. Water voles were not captured below 2440 m. Grazed and ungrazed sites occupied by water voles were matched and analyzed for percent plant cover, dry weight biomass, riparian classification, mean stream depth, channel type, elevation, precipitation, and temperature. Capture success was significantly greater in ungrazed areas. Percent cover by ferns and thallophytes was significantly greater in areas where water voles were more abundant, and bare ground was significantly greater at grazed locations. Water voles were most abundant on Rosgen B or E streams with a willow/wet Carex riparian class that is found on relatively undisturbed sites with stable, well-developed soils and bank structure. In the Big Horn Mountains, water vole captures were low in comparison to the Beartooth Mountains and synergistic effects of grazing and drying might negatively impact this species.

Footprints of Utah's Last Dinosaurs: Track Beds in the Upper Cretaceous (Maastrichtian) North Horn Formation of the Wasatch Plateau, Central Utah

Abstract Dinosaur track beds occur at several localities in the uppermost Cretaceous (Maastrichtian) North Horn Formation in the Wasatch Plateau, central Utah. The track bed localities, separated by up to 80 km, also contain dinosaur body fossils. At the type locality at North Horn Mountain in Emery County, more than 100 individual exposures and/or stratigraphic levels within a 1.2-km2 study area exhibit tracks in vertical cross-sectional view. These biogenic structures are similar to others that have been interpreted elsewhere as deep dinosaur tracks. At the type section, track beds vertically span at least 183 m from the base of the formation up to a few meters below the highest dinosaur eggshells, which are interpreted to occur immediately below the Cretaceous-Tertiary (K-T) boundary interval. Track occurrence in the North Horn Formation demonstrates that large dinosaurs were present in central Utah until very shortly before the K-T boundary. The track structures feature deformation, overprinting, and ...

Faunal implications of an environmental change before the Cretaceous-Tertiary (K-T) transition in central Utah

The North Horn Formation at North Horn Mountain in central Utah records a shift in the composition of the upper Maastrichtian vertebrate fossil assemblage below the Cretaceous-Tertiary (K-T) boundary. Dinosaurs (Alamosaurus,Tyrannosaurus , Torosaurus, and hadrosaurs), turtles (Basilemys), mammals, and lizards(Polyglyphanodon ) occur in the lowest unit of the formation. The environment changed from semi-arid to wetter conditions, and several of the mostly terrestrial vertebrate taxa no longer appeared in the type area. Several taxa that dominated the vertebrate assemblage low in the formation are replaced in the succeeding unit below the K-T boundary by different dinosaur taxa that are represented by eggshells. This altered vertebrate assemblage was more tolerant of, or was adapted to, wetter conditions, but it, too, disappeared at the type locality by the end of the Cretaceous. This wetland dinosaur assemblage is not identical to that found in semi-arid dinosaur assemblages or to dinosaur assemblages in other K-T boundary sites that represent different paleolatitudes. Most of the faunas in the succeeding unit are represented by aquatic forms (crocodilians, turtles, fish, mollusks, and ostracods) which persisted after the dinosaurs disappeared. There appears to be no current tectonic or biostratigraphic reason to conclude that a significant stratigraphic gap exists immediately below the K-T boundary in the North Horn Formation in central Utah.

ABSTRACT: Integration of Mud Gas Isotope Data with Field Appraisal at Horn Mountain Field, Deepwater Gulf of Mexico

ABSTRACT: Integration of Mud Gas Isotope Data with Field Appraisal at Horn Mountain Field, Deepwater Gulf of Mexico

Geology and geochronology of Grenville-age rocks in the Van Horn and Franklin Mountains area, west Texas: Implications for the tectonic evolution of Laurentia during the Grenville

Geology and geochronology of Grenville-age rocks in the Van Horn and Franklin Mountains area, west Texas: Implications for the tectonic evolution of Laurentia during the Grenville

The Story behind "Fetishes—Medicine Wheel"

Photo The Story behind "FetishesMedicine Wheel" by Mark Olencki The tale started innocendy enough. John Lane, one of my oldest friends, asked if I wanted to go out West to visit a mutual friend and drive to as many national parks as we could manage in a week. I eagerly agreed. It would be my first trip west ofthe Mississippi. We flew into BiUings and headed southeast to Buffalo,Wyoming, where our friend Uved. After spending a few days in that small ranch town, John and I took our rented Chevy into the Big Horn Mountains of northern Wyoming. For a photographer from the South who had only experienced the weathered Appalachians, the rugged peaks of the younger Big Horn Mountains were Uke Ansel Adams prints stretched across the windshield. The lucid quality of western light can only be experienced on a few spring and fall days in South CaroUna. UsuaUy the humidity down South is so high it softens the light and makes many photos have that soft-focus quality ofthe turnof -century Pictorialists. That day as we drove higher into the mountains, every turn brought new vistas and opportunities to bring out my equipment and capture in süver nitrate a bit of the awe I experienced. 199 200Fourth Genre As our first day in the mountains closed, we saw and passed a sign for the Medicine Wheel National Monument. John's topo maps told us we were crossing Medicine Mountain. Quickly we turned around and started up the oneand -a-halfmue gravel road to the site. Halfway up we passed a very unusual site, a NASA observatory like a metallic mushroom on the horizon. How odd I thought, but quickly reasoned, why not? In the middle of nowhere, at 9,000 feet, this mountain would be a perfect place to suck the sky with radar. We found out very soon that ancient peoples had the same idea. Arriving at the crude parking area and gate,John and I assembled our respective equipment. I took several cameras—35mm and 120mm format—and John sUpped his notebooks and pens into a daypack. The Medicine Wheel was stiU a half-müe up a dirt path. With theWheel in sight, and the NASA faculty behind us, the trip departed from the norm. As I walked the narrow ridge path to the MedicineWheel, I could see faces in almost every rock formation! They seemed to be silently watching and guarding the thin ridge that led down from the observatory to what we soon saw was a cloth-covered, fenced circle ofwaist-high rocks. I walked the rock edge where it feU off into what was known as the Five Springs Basin. The sentinels were everywhere. I was struck with the feeUng that we were on holy ground. When we met back up, John admitted that he sensed it too. By this time it was late in the day, and I was privileged to get some of the last of a sunset that had long passed in the vaUey below. I walked around the Wheel with my medium format camera in hand. I didn't shoot much because the Ught was quickly fading and so was my film supply. (I had exhausted most of my film on the faces along the ridge below.) Composition as weU as Ught drew me. I walked around theWheel with my medium format camera in hand. I didn't shoot much because the Ught was quickly fading and so was my film supply. (I had exhausted most of my film on the faces along the ridge below.) Composition as weU as Ught drew me—the simple geometry ofbits ofcloth and bone tied to the fence, the mystery of the Medicine Wheel's ornaments. Fetishes, that was the name given to die objects tied on the fence, a ranger told me later. They had been left as favors, reminders to the spirits during private, individual ceremonies ofdianksgiving and praise that occur there daüy. These fetishes were bits of one's unique and powerful individualism, scraps of T-shirts, bandana remnants, coins, jewelry, and smaU animal skuUs. The faces in the rock and the fetishes tied to the...

Response of Desert Ungulates to a Water Project in Arizona

Effects of water projects on ungulates in the arid southwestern United States are poorly understood, but there are concerns that such projects will displace native ungulates, influence movements, and increase mortality. One such project, the Hayden-Rhodes Aqueduct (HRA), traverses the habitat of desert mule deer (Odocoileus hemionus crooki) and bighorn sheep (Ovis canadensis) in southcentral Arizona. We contrasted home range size, use of vegetation associations, and frequency of animal locations within 500 m of the HRA for mule deer in the Belmont and Big Horn mountains and for bighorn sheep in the Little Harquahala Mountains during construction (1980-84) and after completion (1989-92) of the HRA. We also examined the distance of ungulates to water catchments to determine if added water catchments attracted them. Home range size and use of vegetation associations did not differ (P > 0.05) between periods for deer and sheep. Deer and sheep were rarely within 500 m of the aqueduct, but frequency of locations ≤ 500 m of the HRA did not differ (P > 0.05) between, during, and after construction of the canal. Female deer were closer (P < 0.05) to water catchments in spring and summer prior to completion of the canal but farther (P < 0.05) from water catchments in summer after completion of the HRA. Bighorn sheep were not attracted to water catchments. Data suggest that the additional water was not important to the deer or sheep populations. The HRA reinforced previously established barriers (i.e., highways, fences, railroads) that fragmented habitat but did not alter use of habitats or movements of desert mule deer or bighorn sheep

Nocturnal Activity of Female Desert Mule Deer

Most studies of deer activity occur during diurnal hours; nocturnal activity is rarely addressed. For desert mule deer (Odocoileus hemionus crooki), diurnal studies alone may not represent normal activity rhythms resulting from heat stress at certain times of the year. To understand diel activity patterns, nocturnal activity should be examined to see if and how diurnal and nocturnal activities differ. Thus, we quantified nocturnal activity of 5 radio-collared female desert mule deer in the Belmont and Big Horn mountains, Arizona in 1990. We determined their movements and estimated activity with observations and a digital processor. We compared areas used by deer at night with areas used during the day

The Second Jurassic Dinosaur Rush

The first great North American Dinosaur Rush, begun in 1877 and precipitated by the Marsh-Cope rivalry, was followed by an even greater second Dinosaur Rush, begun just before the turn of the century. The two major principals involved were H. F. Osborn of the American Museum of Natural History in New York and W. J. Holland of the Carnegie Museum in Pittsburgh, but a number of other institutions were also involved, among them the Field Museum in Chicago and parties from the Universities of Wyoming and Kansas. The old Marsh sites at Como Bluff, Wyoming and Garden Park, Colorado were reworked with great success, but many new quarries were also opened, among them, those in the Freezeout Hills and eastern slope of the Big Horn Mountains in Wyoming and the Grand Junction area in Colorado, but most importantly at the two greatest North American Jurassic dinosaur sites: The American Museum Bone Cabin Quarry in Wyoming and the Carnegie Museum Quarry at Dinosaur National Monument in Utah.

Grenville-Age, Polyphase Deformation of Mid-Proterozoic Basement, NW Van Horn Mountains, Trans-Pecos, Texas

Psammitic, pelitic, and mafic schists in a basement horst in the NW Van Horn Mountains of west Texas preserve evidence of a multiphase, synmetamorphic, Grenville-age ductile deformation. Three phases of progressive isoclinal folding followed by two later, less intense, nearly coaxial folding phases have been identified. The second phase of deformation produced the dominant foliation and foliatipn-intersection lineation observed throughout the area. This deformation is inferred to have resulted from a regional-scale folding, possibly associated with nappe formation, at or near peak metamorphic conditions. Mineral assemblages indicate amphibolite facies, and Fe-Mg exchange thermometry provide maximum temperatures of corresponding to mid-amphibolite facies conditions. Three subsequent fold generations () formed under progressively lower metamorphic conditions; produced a weakly developed foliation ( ) whereas neither of the two later folding phases formed a penetrative fabric. Fluids or heat associated with the widespread intrusion of late syn- to post-orogenic pegmatites facilitated a static recrystallization event which altered previously formed deformational fabrics. Other basement exposures in the Van Horn area record a later phase of Grenville-age brittle deformation that has wholly or partly obscured the earlier-formed ductile features. The Grenville-age, progressive deformational history recorded in the basement rocks of the Van Horn area is similar to that noted in portions of the Llano Uplift of central Texas and in the Adirondack Mountains of New York and suggests that the Grenville orogeny was characterized by oblique convergence along the length of the North American craton.

Soils and stratigraphy of the laddie creek site (48BH345), an altithermal‐age occupation in the big horn mountains, wyoming

AbstractHaploborolls and Ustifluvents with A‐C horizonation characterize Holocene soil development in alluvium and colluvium of the Laddie Creek valley. Cumulic soils with overthickened A horizons, including those of Altithermal age, have formed along the valley walls under the influence of spring activity from the Amsden Formation (Mississippian‐Pennsylvanian). Soil texture, mineralogy, and to some extent color, are inherited largely from sediment derived from the Amsden and Tensleep (Pennsylvanian) Formations. The valley was able to support human occupation during Altithermal time (ca. 7500‐4000 B.P.) because of springs emanating from the valley walls. Past spring locations are identified from soil morphology and stratigraphy. Springs are still active along the valley, although they have shifted positions many times in the past. The association of spring soils with Altithermal‐age occupation at the site (ca. 6600‐5700 B.P.) does not coincide with the caliche concept of the Altithermal paleosol in Holocene alluvial valleys in Wyoming basins as identified by Leopold and Miller. Nevertheless, early man of Altithermal time probably sought higher elevations within mountains of the region where springs offered water and the environs provided food and shelter—thus enabling human groups to survive the drought, and possible high temperatures, which seemingly prevailed in the basins and plains.

Characteristics of a Hunted Mountain Lion Population in Wyoming

Population characteristics were estimated from June 1981 to July 1983 for a hunted mountain lion (Felis concolor) population occupying a 741-km2 study area in the Big Horn Mountains, Wyoming. Based on the capture-recapture of 46 lions and radio-telemetry, snow-tracking, and harvest data, winter population densities were estimated at 29 km2/lion (1981-82) and 22 km2/lion (1982-83). Sex ratios of 28 kittens and 22 adults did not differ (P > 0.05) from equality. Kittens, born primarily in autumn, comprised about 50% of the population each winter, and 11 postnatal litters averaged 2.7 kittens. Some juveniles dispersed at about 12-15 months of age; 5 were recovered 9-274 km from their natal areas. Two resident females bred at 13and 19-month intervals. The age structure of both sexes was young, the oldest adult being about 7 years old. Observed mortality the 1st year was 27% of the total population and 0% the 2nd year; immigration apparently compensated for mortalities. Home areas of 4 resident females averaged 67 km2 and overlapped almost completely. Those of the 2 resident males overlapped slightly and averaged 320 km2. Male home areas overlapped several female home areas. J. WILDL. MANAGE. 50(4):648-654 Characteristics of unhunted mountain lion populations have been reported in California (Sitton and Weaver 1977; Hopkins et al., in press) and Utah (Hemker et al. 1984). A lightly hunted lion population was described in Idaho (Hornocker 1969, 1970; Seidensticker et al. 1973), and relatively heavily hunted populations were described in Arizona (Shaw 1977), Colorado (Currier et al. 1977), and Nevada (Ashman et al. 1983). This paper reports characteristics of a hunted lion population in the Big Horn Mountains, Wyoming, from June 1981 to July 1983. Impetus for this study was provided by the lack of detailed biological data on lions in Wyoming; information previously was limited to general status reports. Day and Nelson (1929, cited in Nowak 1976) reported that the species was very scarce, and Young (1946) said it was confined mainly to the western mountains. Long (1965:705) believed the lion was nearly extirpated by the early 1960's. Roop (1971) indicated that lions were scarce and restricted to relatively inaccessible areas. Berg et al. (1983) conducted a mail survey in Wyoming and concluded the state's lion population was stable or had increased during the last 10 years, particularly in the Big Horn Mountains. Long-term resident ranchers and trappers in our study area corroborated this apparent, recent increase in mountain lions. This study was funded by the Wyo. Coop. Fish. and Wildl. Res. Unit and the Wyo. Game and Fish Dep. The Sheridan Work Unit of the U.S. Fish and Wildl. Serv. provided radio-telemetry equipment. Assistance also was provided by the Univ. Wyoming, the U.S. Bur. Land Manage., and the U.S. For. Serv. M. E. Bush, J. Hyde, and J. Childs assisted in a variety of important ways. We also are grateful to C. M. Gillin and H. L. Osborn, our technicians, and to the private landowners who cooperated with us during this study. S. H. Anderson, W. G. Hepworth, E. T. Thorne, T. J. Killough, and R. L. Phillips provided valuable support. We thank M. L. David for typing the manuscript.

Two New Species of Cymopterus (Umbelliferae) from Western North America

Two species ofCymopterus are described as new:Cymopterus douglassi from the Lost River and Lemhi ranges of central Idaho and the closely relatedC. williamsii from the southern half of the Big Horn Mountains, Wyoming. Both are diploid on the basex=11 and occur on calcareous or dolomitic substrates. The mature fruit ofCymopterus williamsii differ from those ofC. douglassii in the absence of a functioning carpophore and in having 1, not 3–5 oil tubes in the intervals. Both species are unusual in the genus, though not unique, in that the dorsal ribs of the mericarps are not winged.

The Effect of Breed, Sex and Carcass Weight on the Composition of Lamb Retail Cuts

Because the majority of lamb in Britain 1s sold to the consumer ‘bone-In’ it 1s difficult to trim excessive fat. Nevertheless, consumer acceptability of specific retail cuts 1s markedly affected by the fat content of that joint at the point of sale. Therefore, any strategy which aims to define breed-specific carcass weights at slaughter needs to consider the effect this will have on retail joint weights, their composition and hence acceptability. This study examined the effect of breed, sex and carcass weight on the proportions of the four main lamb cuts, and their composition.In this study a total of 317 castrated males and 238 females from six pure breeds (Clun Forest, Dorset Horn, Hampshire Down, Suffolk, Colbred and Welsh Mountain), were slaughtered in. the conventional manner. The range 1n cold carcass weight (CCW) was from 12 to 24 kg. Carcasses were jointed and each of the nine joints then dissected into lean, bone, subcutaneous fat (SCF) and intermuscular fat (IMF) (Brown and Williams, 1979)1 For ease of presentation the data for nine joints were reduced to four by combining some of them. The shoulder Included the neck, the breast Included the brisket and flank, the leg Included the upper and lower leg and the loin included the best end of neck.

Introduction to Stratigraphy, Structure, and Geologic Problems in Big Horn Basin, Wyoming and Montana: ABSTRACT

End_Page 1342------------------------------As the cumulative production of oil from the Big Horn basin approaches the 2 billion bbl mark, it is appropriate that we look at the geology once again. The Big Horn basin, located in northwestern Wyoming and south-central Montana, is bordered on the east by the Big Horn Mountains; on the south by the Owl Creek Mountains; on the west by the Absaroka and Beartooth Mountains; and on the north by the Nye-Bowler lineament. The combination of a great reservoir-source duet in the Paleozoic rocks and the creation of large anticlines during the Laramide orogeny has been the key to the Big Horn basin's success as an oil producer. Stratigraphy of the Big Horn basin can be divided generally into (1) the Middle Cambrian clastics, (2) the Paleozoic shelf carbonates, (3) the Mesozoic clastics, (4) the Late Cretaceous to Tertiary synorogenic clastics, and (5) the Tertiary post-orogenic clastics and volcanics. By far the most economically important formations have been the Permian Phosphoria and Pennsylvanian Tensleep Formations. This dynamic duo consists of porous eolian and shallow marine, quartz sandstones of the Tensleep overlain by shallow marine, oil-rich carbonates of the Phosphoria. The two have combined to produce over 1.5 billion bbl of oil in the Big Horn basin alone. The draping of the Tensleep and Phosphoria over large Laramide structures (closures of over 5,000+ ft, 1,500 m, and areal extents up to 15 mi2, 40 km2) was the final key. An upcoming afternoon session of papers will explore the proposed anatomies and mechanisms of folding in the Cordilleran foreland. There is a controversy over the morphology of the folds in the foreland. Put simply, there is some disagreement over how much the horizontal or thrusting component contributes to these folds. Stearns, who described the fold at Rattlesnake Mountain in the 1971 Wyoming Geological Association guidebook, favors drape folding over near-vertical faults in the Precambrian. Berg in the 1962 AAPG Bulletin and Gries in the 1983 AAPG Bulletin favor a more thrusted model with reverse fault planes dipping 60° to 30°. Sales in the 1968 AAPG Bulletin agrees with the morphology of Berg and Gries, but feels that the folds in the foreland were generated by faults with strong lateral components. Concerning other problems, Stone in the October 1967 AAPG Bulletin pointed out that the Paleozoic reservoirs often have a common oil-water contact (OWC) within individual structures. He attributed the common OWC to fractures joining the reservoirs. The OWC is commonly tilted; this he attributed to hydrodynamic flow. An understanding of fractures and tilted oil-water contacts is imperative for successful exploration and production programs in the Big Horn basin. End_of_Article - Last_Page 1343------------

Oil and Gas Prospecting Beneath Precambrian of Foreland Thrust Plates in Rocky Mountains

Only 16 wells in the Rocky Mountain region have drilled through Precambrian rocks to test the 3 to 6 million acres of sedimentary rocks that are concealed and virtually unexplored beneath mountain-front thrusts. One recent test is a major gas discovery, another a development oil well, and over half of the unsuccessful tests had oil or gas shows. These wells have not only set up an exciting play, they have also helped define the structural geometry of the mountain-front thrusts, including the angle of the thrust, the amount of horizontal displacement, and the presence or absence of fault slivers containing overturned Mesozoic or Paleozoic rocks. Important for further geophysical exploration, these wells have provided vital data on seismic velocities in Precambrian rocks. A alysis of these data has stimulated further exploration along the fronts already drilled: in Wyoming, the Emigrant Trail thrust, the Washakie thrust, the Wind River thrust, the thrust at the north end of the Laramie Range, and the Casper arch; in Utah and Colorado, the Uncompahgre and Uinta uplifts. The geologic success of these wells has encouraged leasing and seismic acquisition on every other mountain-front thrust in the Rockies. An unsuccessful attempt to drill through the Arlington thrust of the Medicine Bow Range will probably only momentarily daunt that play, and the attempted penetration of the Axial arch in Colorado has not condemned that area; in fact, another well is being drilled at this time. Untested areas that will be explored in the near future are: in Wyoming, the south flank of the Owl Creek Range, the southwest flank of the Gros Ventre Range, the east and west flanks of the Big Horn Mountains, the west flank of the Big Horn basin, the north flank of the Hanna basin; in Utah, the south flank of the Uinta Mountains; and in Colorado, the White River uplift, the no th flank of North Park basin, and the Front Range.

Oil and Gas Prospecting Beneath Precambrian in Rocky Mountains: ABSTRACT

Although the Rocky Mountains have their first large sub-Precambrian hydrocarbon discovery, only 15 wells have been drilled through Precambrian to test the 3 to 6 million acres (1 to 2 million ha.) of sedimentary rocks that are concealed and virtually unexplored beneath mountain front thrusts. More than half of these wells had oil and gas shows and one was a producing development oil well. These wells have not only set up an exciting play for the future, they have also helped define the structural geometry of the mountain front thrusts of the Rocky Mountain foreland, including the angle of the thrust and the presence or absence of fault slivers of overturned Mesozoic or Paleozoic rocks. Most important for further geophysical exploration, these wells have provided vital dat on seismic velocities in Precambrian rocks. Analysis of these data will stimulate further exploration along the fronts already drilled: the Emigrant Trail thrust, the Washakie thrust, the Wind River thrust, the Uinta Mountain thrust, and the thrust at the north end of the Laramie Range. The geologic success of these wells has encouraged leasing and seismic acquisition on every other mountain front thrust in the Rockies. Wells are presently being drilled on the Casper arch and the west flank of the Big Horn basin adjacent Oregon Basin field. An unsuccessful attempt to drill through the Arlington thrust of the Medicine Bow Range will probably only momentarily daunt that play, and the attempted penetration of the Axial arch in Colorado has not condemned that area. Untested areas that will be explored in the near future are: the south flank of the Owl Creek Range, the northeast flank of the Beartooth Mountains in Montana, the east and west flanks of the Big Horn Mountains, the north flank of the Hanna basin, the south flank of the Uinta Mountains, the White River uplift, the north flank of North Park basin, and the Front Range. End_of_Article - Last_Page 1180------------

Oil and Gas Prospecting Beneath the Precambrian of Foreland Thrust Plates in The Rocky Mountains

Only 15 wells in the Rocky Mountain region have drilled through Precambrian to test the 3-6 million acres of sedimentary rocks that are concealed and virtually unexplored beneath mountain front thrusts. More than half of these wells had oil and gas shows and one was a producing oil well. These wells have not only set up an exciting play for the future, they have also helped define the structural geometry of the mountain front thrusts, including the angle of the thrust and the presence or absence of fault slivers of overturned Meso­zoic or Paleozoic rocks. Most important for further geophysical exploration, these wells have provided vital data on seismic velocities in Precambrian rocks. Analysis of these data will stimulate further exploration along the fronts already drilled. the Emigrant Trail Thrust, the Washakie Thrust, the Wind River Thrust, the Uinta Mountain Thrust, and the thrust at the north end of the Laramie Range. The geologic success of these wells has encouraged leasing and seismic acquisition on every other mountain front thrust in the Rockies. Wells are presently drilling on the Casper Arch and the west flank of the Big Horn Basin adjacent Oregon Basin Field. An unsuccessful attempt to drill through the Arlington Thrust of the Medicine Bow Range will probably only momentarily daunt that play, and the attempted penetration of the Axial Arch in Colorado has not condemned that area. Untested areas that will be explored in the near future are: the south flank of the Owl Creek Range, the northeast flank of the Beartooth Mountains in Montana, the east and west flanks of the Big Horn Mountains, the north flank of the Hanna Basin, the south flank of the Uinta Mountains, the White River Uplift, the north flank of North Park Basin, and the Front Range.