Northwest Colorado Research Articles

Control of Earthquakes at Rangely, Colorado: ABSTRACT

Following the experience with earthquakes at the Rocky Mountain Arsenal, it was recognized that there might be other places where earthquakes were triggered by fluid injection. In fact, Griggs suggested that it might be possible to control earthquakes by controlling subsurface fluid pressures. A seismic observatory at Vernal, Utah, reported many earthquakes near the Rangely oil field in northwest Colorado. The U.S. Geological Survey observed earthquakes in the field for one month in 1967 and established two active zones, both on the periphery of the field, both areas of waterflooding and high reservoir pressure. In 1969, the U.S. Geological Survey began a four-year experiment to control earthquakes along one active fault. Through an arrangement with Chevron Oil Company, the operator of the Rangely unit, the U.S. Geological Survey gained operating control of four water-flood injection wells in one of the zones of earthquake activity. The experiment was conducted in three phases: (1) an initial phase of reducing fluid pressure, an attempt to stop the earthquakes; (2) a second phase of reinjection and increased pressure, an attempt to reactivate the fault; and (3) a fluid phase of reducing pressure, an attempt to terminate earthquake activity along the fault. The experiment was completed successfully during the summer, 1973. The results demonstrate conclusively that by controlling the effective tress through the injection and withdrawal of fluids, it was possible to control earthquakes, at least in favorable geologic environments. End_of_Article - Last_Page 1432------------

Stratigraphy of Frontier Sandstone Member of Mancos Shale (Upper Cretaceous) on South Flank of Eastern Uinta Mountains: ABSTRACT

The stratigraphy of the Frontier Sandstone Member of the Mancos Shale (Upper Cretaceous) was studied on the south flank of the eastern Uinta Mountains (northwest Colorado and northeast Utah). The Frontier Sandstone Member (about 275 ft thick) is divided into 5 depositional units, A through E, which are identified on outcrop by their stratigraphic position, lithology, and inorganic and organic structures. These depositional units are distinct local stages of a full cycle of deltaic sedimentation in the study area. Units A and B represent sedimentation under an encroaching shoreline from the west with a gradual vertical grain-size increase from black shale and siltstone to very fine-grained, fossiliferous sandstone. Unit C represents a further regression of the shoreline with the development of a littoral zone in and near the study area. Unit D, representing the height of the constructional End_Page 1392------------------------------ phase of the delta, is a complex of various lithologies which is divided into 4 major facies: coastal swamp, fluvial estuary, barrier island, and neritic marine. The fluvial estuary is open landward to a major distributary channel and exhibits high-energy, fluviatile bed forms. The barrier island sandstone body shows a N65°E orientation and separates 2 major facies--the coastal swamp/fluvial estuary facies on the northwest and the neritic marine on the southeast. Ophiomorpha burrows, indicators of littoral and shallow neritic environments, are common throughout the barrier-island sandstone. Unit E represents the destructional phase of the delta with initial deposition of marine black shale capping the complex of deltaic sediments of unit D. A grainsize increase upward through uni E, to fine-grained sandstone, culminates in the development of linear, offshore sandstone bars in the upper part of the interval. The sandstones have been bioturbated thoroughly by detritus feeders. Paleorelief, caused by the underlying stratigraphy of unit D, influenced the distribution of the unit E sandstone. Paleotopographic depressions found over the previous positions of both the subshore-face facies of the barrier-island sandstone and the coastal swamp facies, received the thickest offshore sandstone bar development, whereas paleotopographic ridges, specifically above the barrier-island sandstone, received the thinnest offshore bar development. No significant paleorelief was present at the end of the deposition of unit E and the beginning of the deposition of the upper shale memb r of the Mancos Shale. The zircon:tourmaline ratio, determined by heavy-mineral analysis of the sandstones, can be used to differentiate fluvial and marine sandstones. Because zircon (Sp. G. 4.7) and tourmaline (Sp. G. 3.1-3.3) have widely different specific gravities, their relative abundances can be used as sensitive indicators of depositional environments. This sorting is related to the particular energy regime which existed at the time of deposition. Ratios greater than 1:1 are representative of high-energy fluvial sandstones, and ratios less than 1:1 are representative of low-energy marine sandstones. The marine environment can be subdivided further between shallow neritic (barrier islands, offshore bar, and shoreface environments) and deeper neritic with the shallow neritic having abundant heavy miner ls and the deeper neritic having rare heavy minerals. End_of_Article - Last_Page 1393------------

Stratigraphy of Frontier Sandstone Member of Mancos Shale (Upper Cretaceous) on South Flank of Eastern Uinta Mountains: ABSTRACT

The stratigraphy of the Frontier Sandstone Member of the Mancos Shale (Upper Cretaceous) was studied on the south flank of the eastern Uinta Mountains (northwest Colorado and northeast Utah). The Frontier Sandstone Member (about 275 ft thick) is divided into 5 depositional units, A through E, which are identified on outcrop by their stratigraphic position, lithology, and inorganic and organic structures. These depositional units are distinct local stages of a full cycle of deltaic sedimentation in the study area. Units A and B represent sedimentation under an encroaching shoreline from the west with a gradual vertical grain-size increase from black shale and siltstone to very fine-grained, fossiliferous sandstone. Unit C represents a further regression of the shoreline with the development of a littoral zone in and near the study area. Unit D, representing the height of the constructional End_Page 1392------------------------------ phase of the delta, is a complex of various lithologies which is divided into 4 major facies: coastal swamp, fluvial estuary, barrier island, and neritic marine. The fluvial estuary is open landward to a major distributary channel and exhibits high-energy, fluviatile bed forms. The barrier island sandstone body shows a N65°E orientation and separates 2 major facies--the coastal swamp/fluvial estuary facies on the northwest and the neritic marine on the southeast. Ophiomorpha burrows, indicators of littoral and shallow neritic environments, are common throughout the barrier-island sandstone. Unit E represents the destructional phase of the delta with initial deposition of marine black shale capping the complex of deltaic sediments of unit D. A grainsize increase upward through uni E, to fine-grained sandstone, culminates in the development of linear, offshore sandstone bars in the upper part of the interval. The sandstones have been bioturbated thoroughly by detritus feeders. Paleorelief, caused by the underlying stratigraphy of unit D, influenced the distribution of the unit E sandstone. Paleotopographic depressions found over the previous positions of both the subshore-face facies of the barrier-island sandstone and the coastal swamp facies, received the thickest offshore sandstone bar development, whereas paleotopographic ridges, specifically above the barrier-island sandstone, received the thinnest offshore bar development. No significant paleorelief was present at the end of the deposition of unit E and the beginning of the deposition of the upper shale memb r of the Mancos Shale. The zircon:tourmaline ratio, determined by heavy-mineral analysis of the sandstones, can be used to differentiate fluvial and marine sandstones. Because zircon (Sp. G. 4.7) and tourmaline (Sp. G. 3.1-3.3) have widely different specific gravities, their relative abundances can be used as sensitive indicators of depositional environments. This sorting is related to the particular energy regime which existed at the time of deposition. Ratios greater than 1:1 are representative of high-energy fluvial sandstones, and ratios less than 1:1 are representative of low-energy marine sandstones. The marine environment can be subdivided further between shallow neritic (barrier islands, offshore bar, and shoreface environments) and deeper neritic with the shallow neritic having abundant heavy miner ls and the deeper neritic having rare heavy minerals. End_of_Article - Last_Page 1393------------

Age Distributions of Spruce and Fir in Beetle-killed Forests on the White River Plateau, Colorado

In the 1940's an epidemic of the Engelmann spruce beetle (Dendroctonus engelmannii Hopk.) killed almost all the spruce (Picea engelmannii (Parry) Engelm.) and most of the fir (Abies lasio- carpa (Hook.) Nutt.) larger than 10 cm in diameter breast height, on the White River Plateau, in northwest Colorado. Reconstruction of the age distributions of spruce and fir at the time of the beetle attack were made by counting all the dead trees, stumps and live trees in two stands and estimating the ages of these trees at the time of the beetle attack. The resulting age distributions indicate a reduction in spruce reproduction in the late 1700's, while fir reproduction was relatively unchanged. An epidemic of Engelmann spruce beetles in the early 1700's is suggested to explain these age distributions. Fire, climatic change, or grazing and trampling by cattle are less likely hypotheses. INTRODUCTION AND BACKGROUND The White River Plateau is a subalpine plateau located in north- western Colorado, north of Glenwood Springs, in Garfield and Rio Blanco counties. The plateau is bordered on the south and southeast by the Colorado River, on the northeast by the Yampa River, and on the north by the north fork of the White River. The central part of the Plateau is drained by the south fork of the White River. Most of the present surface of the Plateau lies between 3050 and 3350 m elevation and may be described as rolling, broken here and there by rocky out- crops and deep canyons cut by the major streams draining the area. The vegetation is composed of about 50% forests of Engelmann spruce (Picea engelmannii (Parry) Engelm.) and subalpine fir (Abies lasio- carpa (Hook.) Nutt.) and about 50% meadow. Forests of spruce and fir with patches of meadow predominate on north and northeast ex- posures while meadows containing isolated spruce trees and patches of several spruce and fir predominate on south and southwest exposures. In the 1940's, following a severe wind and blowdown, an epidemic of Engelmann spruce beetles (Dendroctonus engelmanni Hopk.) killed almost all spruce larger than approximately 10 cm diameter breast height. The beetles killed the larger trees first and then pro- gressed through smaller trees. Between 1940 and 1944 the average diameter of trees killed was 53 cm; in 1945, the average diameter of trees killed was 43 cm, and in 1946, 38 cm. The average diameter of live spruce at the end of 1946 was 34.3 cm. By 1948 most of the spruce larger than 10 cm diameter breast height - were dead (Massey and Wygant, 1954). Some of this beetle-killed spruce was lumbered in the early 1950's. Preliminary reconnaissance in 1962 and 1963 indicated that at the time of the 1940 spruce beetle epidemic the forests were not composed of an uneven-aged stand of trees, as one might expect if the forest had

Developments in Eastern and Northwestern Colorado and Western Nebraska in 1967

The Denver basin of Colorado and Nebraska was the site of 77.5% of all exploratory drilling in the report area, and the productive trend was extended southwestward by a 1967 discovery. It is believed that exploratory activity will increase in the sparsely drilled southwest part of the basin during 1968, and that exploration in the rest of the Denver basin will continue at about the same level as in 1967. Exceptional success in the development of production from the Dakota (Cretaceous) in northwest Colorado and the Mississippian in southeast Colorado, coupled with an increase in geophysical activity in these 2 areas during 1967, will insure increased exploration in the 2 regions in 1968.

Economics of Oil Shale: ABSTRACT

Most shale-oil production cost estimates are between $1.25 and $2.10 per bbl. of pipeline crude produced from oil-shale deposits in northwest Colorado. Two companies have not released cost figures, but Union states that a 27½% depletion allowance is necessary before shale can be developed commercially. Other companies and organizations have conducted or are conducting shale-research projects, but none has published firm shale-oil cost estimates. M. A. Lekas of the Atomic Energy Commission has speculated that costs of producing shale oil may be as low as $0.29/bbl. He maintains that these costs can be achieved by using nuclear blasts to create permeable, underground, in situ retorting chambers. The A.E.C. hopes to detonate such a test soon in oil shale. The recent discoveries of valuable sodium minerals commingled with oil shale in the center of the basin may change significantly the economics of production. The problems confronting this unborn industry are well known. The decision to start the industry should be based on the optimum combination of land, reserves, technology, operators, market, legal status, political, and governmental support. The decision can not be made unless these factors can be combined reasonably and with the knowledge that the conditions governing them are relatively stable. End_of_Article - Last_Page 2030------------

Geologic History of Piceance--Eagle Basin: ABSTRACT

The Piceance and Eagle basins represent the present expression of the Maroon trough or basin that started to develop in Early Pennsylvanian time. It extended across northwest Colorado and was bounded by the positive elements of the Front Range on the northeast and the Uncompahgre on the southwest. The early sediments are clastics, carbonates, and evaporites resulting from cyclic marine transgressions and regressions in the narrow trough. The evaporites are of the basin-center type, according to Sloss, but strongly affected by contemporaneous clastic deposition. The growth of the Front Range in Morrowan time and the uplift of the Uncompahgre in Desmoinesian time contributed large volumes of sediments to the trough during the regressions, which became interbedded with the e aporites. The coarse clastics from the Front Range and Uncompahgre continued to strongly influence the sedimentary types of the Maroon basin throughout the Triassic and Jurassic deposition, with the predominant type being arkoses and redbeds. In Cretaceous, the area was inundated by the Cretaceous sea where the sedimentation was black shales, marine sands, bars and beach deposits. In Upper Cretaceous the entire basin became a shallow sea with paludal and lagoonal sediments, such as coals, shales, and underclays being interbedded with shoreline sands in response to fluctuations of the sea. Some of the older structural features, such as the Douglas arch, began to influence sedimentation during Upper Cretaceous, as evidenced by thinning in the Mancos Shale over the arch. After prolonged sedimentation, the Maroon basin was uplifted at the end of Mesozoic time, and folded and faulted by the Laramide orogeny. The Sawatch Range, White River uplift, and the Uinta Mountains came into being in successive stages of the orogeny to separate the Maroon basin into the present tectonic basins; namely, the Piceance basin, the Eagle basin, the Axial basin, the Coyote basin, and the Sand Wash basin. Many of the present-day structural features were formed during the long period of orogeny from Late Cretaceous to early Tertiary time. Sedimentary types have been most important in determining the reservoirs for the accumulation of oil and gas following the Laramide period of orogeny. Virtually all the oil and gas in the Paleozoic in the Maroon basin has been produced from the Weber Sandstone. It is a lithologic facies having some permeability and effective porosity, that was at the same time sufficiently brittle to fracture. The porosity and permeability alone are insufficient in many of the fields to support commercial rates of production. In addition to the sedimentary type, folding has been all important in establishing substantial reserves with respect to the Paleozoic accumulations. The same control of the fracturing and sedimentary type applies to Cretaceous and Tertiary reservoirs in the Piceance basin, even though the role of folding is not a prime prerequisite to accumulation. All the important Cretaceous and Tertiary oil and gas fields are related to the local improvement of porosity and permeability above and beyond that normal to the marine shales encasing the reservoirs. In contrast to the normal relationships of gas, oil, and water found in the Paleozoic reservoirs, many of the same relationships are reversed in the Cretaceous and Tertiary reservoirs. The relationships are similar to those in the San Juan basin and may have a similar explanation. More realistically, the explanation may be the indigenous nature of the oil and gas, where the migration has been limited to reservoirs in juxtaposition with the source beds. Successful exploratory programs must be cognizant of the fact that the location of the areas of improved porosity and permeability became the primary reason for success. That success can be frustrated by inappropriate drilling and completion methods. End_of_Article - Last_Page 1876------------

Developments in Colorado and Western Nebraska in 1960

Total wells drilled (906) in Nebraska during 1960 represented a 5% decrease from 1959, although exploratory drilling increased 6.1%. Success ratio for wildcat wells was 10.4%. Most significant were 6 new fields discovered on the west flank of the Cambridge arch, where in addition to Lansing-Kansas City production, Reagan sand (Cambrian (?)) was found productive at Sleepy Hollow. Total production in western Nebraska for 1960 was 23,921,487 bbls., an increase of 5.9% over the 22,584,096 bbls. produced in 1959. The Denver basin production increase amounted to only 2.6%, whereas Cambridge arch production increased over 806%. Drilling in Colorado totaled 703 wells, a decline of 16.1% from 1959. Exploratory drilling in eastern Colorado decreased 76.7%, while wildcat wells in western Colorado increased 11.8% over 1959. Success ratios for the two areas were 11.9% and 16.7%, respectively. Foremost in importance was the discovery of gas and condensate from the Mississippian and Devonian rocks at Southeast Lisbon in the Colorado part of the Paradox basin. Six gas fields and two oil fields were found in northwest Colorado, including a significant Weber (Pennsylvanian) discovery on the Danforth Hills anticline and several Cretaceous Mancos-Mesaverde transition zone gas discoveries. Total production in Colorado for 1960 was 47,427,297 bbls., a 2.1% increase of 973,885 bbls. over the 46,453,412 bbls. produced in 195 . Geophysical activity increased sharply on the Cambridge arch, south-central Nebraska, and in the Paradox basin of southwest Colorado, the latter area accounting for 54% of total seismic work in Colorado and Nebraska. These same areas provided the most active regions, leasing and trading-wise. The decline in Denver basin Cretaceous exploration, which was sharply down in 1960, is expected to continue during 1961. However, this will undoubtedly be offset by continued increased activity in western Colorado and on the Cambridge arch of south-central Nebraska. Changes during 1960 in the Mineral Leasing Act involving increased annual rentals of Federal lands will probably cause a more rapid evaluation of such lands during 1961.

Upper Cretaceous Stratigraphy, Rocky Mountain Area

Upper Cretaceous rocks of the Rocky Mountains are characterized by intertonguing of marine and non-marine sediments. Along the western margin of the Rocky Mountain area deposits are nearly all nonmarine. Tongues of these sediments extend eastward across the Rocky Mountains and pass by reason of facies change into marine shale sequences. In this intertonguing relationship four principal facies can be recognized in the Upper Cretaceous which are directly related to the environments of deposition. In the marine environments, white or gray, limestone or marlstone was deposited in the offshore deeper neritic environment, and gray or black shale with thin beds of limestone, siltstone, or sandstone in the offshore shallow neritic environment. White, gray, or tan thin- to massive-bedded sandstone was deposited in the transitional and shallow neritic environment. In the non-marine swamp, lagoon, coastal plain, inland, and piedmont environments gray clay and shale and tan lenticular sandstones with beds of coal, carbonaceous shale, or conglomerate were deposited. Formation names in the Cretaceous of the Rocky Mountains usually correspond with facies of local areas. Many formation names are used improperly among intermontane basins of the Rocky Mountains. Six diagrammatic restored sections of Upper Cretaceous rocks show that the dominant sedimentary pattern during Late Cretaceous was deposition during regression of the strandline from west to east, across the present Rocky Mountains area. This regressive pattern periodically was broken by sharp transgressions of the strandline, resulting in intertonguing of marine and non-marine beds. Four major transgressions and four major regressions of the strandline can be delineated. The positions of the strandline of the late Cretaceous sea, at maximum advance and retreat, are traced regionally on three maps. The relationship of formation names to Upper Cretaceous lithogenetic units is shown on restored sections and maps. Lithologic sequences were deposited during both regressive and transgressive events, which have been miscorrelated in the past. Regional correlations show that the non-marine coal-bearing shale and sandstone tongue called in northwest Colorado and in Wyoming is younger than the Mesaverde formation at its type locality in the San Juan Basin of southwest Colorado. The of northwest Colorado and in Wyoming is correlative with the Judith River formation of Montana. The shale of its type locality in the San Juan Basin is correlative with the upper part of the Mancos shale of northwest Colorado and the upper part of the Steele shale of Wyoming.Thus, the Lewis shale of northwest Colorado and Wyoming is younger than shale at the type locality, and is correl tive with Bearpaw shale of Montana.

Some Remaining Potentials of Northwest Colorado: ABSTRACT

The history of production in northwest Colorado lends background to the problems of the exploration geologist in the region such as: the paucity of geologic literature specifically on the region and the resultant hodge-podge of stratigraphic and structural nomenclature therein, the presence of severe Laramide deformation masking older structure, and the high cost of exploration. The Eastern Uinta-Axial arch-White River uplift structural element has potential in undiscovered structural traps similar to those now producing and in the older section with included evaporites, clastics, and carbonates of Pennsylvanian and Mississippian age which point to the similarity between the Eagle and Paradox basins. The Piceance basin has potential based on the thinning of the pre-Green River-post-Mancos section, with its thousands of feet of included sand, westward from the White River uplift onto the Douglas arch. A third selected potential is the stratigraphic possibilities present in the upper Mancos-Mesaverde beach and bar sands deposited over the region by a generally but sporadic northeastward regressing sea. The potential of the Mancos fracture production has not been realized in that exploration and hence production to date have been restricted to closures probably because these have invited drilling, and that other fracture accumulations will be discovered off-structure where adequate vertical stress has been applied to form fracturing. The need for the exploration geologist in northwest Colorado is to turn his primary interest from the search for structural closure to detailed stratigraphic study and to correct technical interpretation and application of data at hand. Finally the geologist must wean managing departments away from grading prospects on closure alone and sell them on accepting and drilling prospects uncovered by this less orthodox approach. End_of_Article - Last_Page 1094------------

Possibilities of Weber Stratigraphic Traps, Rangely Area, Northwest Colorado

The purpose of this study is to determine the possibilities of stratigraphic hydrocarbon accumulation in the Weber formation, especially in the general area of Rangely, Colorado. Outcrop descriptions, core analyses and descriptions, sample examinations, flowmeter surveys, production data, and test data were utilized in drawing conclusions. During early Pennsylvanian time a shallow trough extended from the geosynclinal Oquirrh basin eastward upon the broad shelf. Apparently this east-trending seaway intermittently connected the Oquirrh basin with the central Colorado trough. The Morgan and Weber formations are believed to be shelf-deposited equivalents of the Permo-Pennsylvanian geosynclinal Oquirrh formation. As such, the Weber transects the Permo-Pennsylvanian time boundary. The Uncompahgre and Park Range uplifts became very active in early Des Moines time. Clastics from the Uncompahgre uplift spread north, and northwest into the shallow trough and westward into the Oquirrh basin. The arkosic Maroon formation forms a wide belt around the uplift areas. The Maroon interfingers with and is overlapped by the relatively cle n quartzose sandstone of the Weber. Therefore, the Maroon formation is essentially a near-source facies variation of the Weber formation. The Weber formation contains beds with more favorable reservoir characteristics than the Maroon. Consequently the possibility of significant stratigraphic trapping of hydrocarbons along the Weber-Maroon facies change is good. Both Rangely and Thornburg fields are located within this facies change, and may have been in areas of general oil accumulation prior to the formation of local structural traps by Laramide folding.

Petroleum and Natural Gas in the Non-Marine Wasatch Formation of Northwest Colorado and Southwest Wyoming: ABSTRACT

The development during the past few years of commercial volumes of petroleum and natural gas in the Wasatch formation of northwest Colorado and southwest Wyoming has aroused considerable geological comment. The Wasatch formation is of Eocene age and fluvio-terrestrial in origin. Geological field studies have established Wasatch sedimentation as of the continental type and definitely non-marine. Petroleum and natural gas have been developed in and are now being produced from the Hiawatha member of the lower Wasatch. The production is believed to be indigenous to the Wasatch formation and not migratory from other formations. The occurrence of hydrocarbons in large volumes in a non-marine formation, and apparently indigenous thereto, is most unusual geologically. The commercial accumulation of both petroleum and natural gas in the Wasatch formation appears to be controlled, in the main, by structural folding. However, the extreme lenticularity of the Wasatch sands and the resulant stratigraphic traps formed by sand lensing are of more importance locally than structural position in determining successful well locations. Over 25 separate gas productive lenses and five separate oil-productive lenses of variable sizes and shapes are already known to occur in the Hiawatha member of the Wasatch formation. Four fields, namely, East Hiawatha, West Hiawatha, Powder Wash, and Canyon Creek have found commercial volumes of natural gas in Wasatch sand lenses. Two of them, East Hiawatha and Powder Wash, are productive of commercial quantities of petroleum, as well as natural gas, from the same Wasatch formation. The economical development of petroleum and natural gas fields in the lenticular and somewhat erratic sands of the continental Wasatch formation involves production problems and hazards not common to the more regular sand-reservoir fields. End_of_Article - Last_Page 900------------

Petroleum and Natural Gas in Non-Marine Sediments of Powder Wash Field in Northwest Colorado

The occurrence of considerable volumes of petroleum (1,000 barrels per day) and natural gas (34,000,000 cubic feet per day) in non-marine sediments of the Powder Wash field in northwest Colorado has recently attracted much attention. The petroleum and natural gas production occurs in continental deposits of Lower Eocene age known as the Hiawatha member of the Wasatch formation. Production is believed to be indigenous to the non-marine Wasatch formation and not migratory from either underlying or overlying formations. Saline waters occur in association with the petroleum-producing zones. Accumulation apparently is controlled by an upfolded Tertiary dome structure but within the confines of the structure producing horizons are extremely irregular. This irregularity is large y due to the highly lenticular sand bodies which are characteristic of the continental Wasatch formation. The Powder Wash field is discussed as an example of a field productive of both petroleum and natural gas from non-marine sediments. The stratigraphy of the region and general structural conditions are described in some detail to prove as untenable any assumption of vertical migratory movement of hydrocarbons from other formations and any assumption of long-distance lateral migration is shown to be equally unsupportable. Two hypotheses to account for the presence of hydrocarbons in the non-marine sediments at Powder Wash are presented. The unusual hazards involved in developing such fields in the Wasatch continental formation are discussed.

Unit Operation as Proposed for the Hiawatha, South Baxter Basin and North Baxter Basin Gas Fields in Southwest Wyoming and Northwest Colorado

The three gas-producing "pools" discussed in this paper are inSweetwater County, southwest Wyoming, and Moffat County, northwest Colorado.Hiawatha,.North Baxter Basin and South Baxter Basin gas fields becameeconomically important in 1929 when a 330-mile gas line connected them withSalt Lake City, Ogden and towns en route. This development immediately focussedattention on the gas-producing fields and the efforts of the producing companyto develop them in an orderly, economical manner. Several outstanding interestswere acquired and working agreements made with others.

Geology of Vermilion Creek Gas Area in Southwest Wyoming and Northwest Colorado

The Vermilion Creek gas area, located on both sides of the state line between southwest Wyoming and northwest Colorado, is now the field terminus of a 330-mile $20,000,000.00 gas line built in 1929 and supplying Salt Lake City, Utah, and adjacent towns with natural gas. The gas developed here is the first important commercial gas developed in the Tertiary formations of the Rocky Mountain region. Six closed domes, three of which are associated with considerable faulting and four of which are controlled by one main line of anticlinal folding, are developed. The folding in the gas area is a direct consequence of the older and more severe regional structural movements in the Uinta Mountains on the south and west and the Rock Springs uplift on the northwest. To date two of the domes have been proved for commercial gas, one well yielding a total of 65,000,000 cubic feet per day from four separate sands. The gas is produced from irregular sand bodies, very lenticular and physically different, in the lower Wasatch formation of Eocene Tertiary age. The producing horizons are of fresh-water origin only. Gas accumulation is controlled by the folding of the Tertiary beds into closed structures. The source of the gas, which is of excellent quality, is not exactly known. Examination of outcrops and of drill cuttings reveals comparatively scanty evidence of organic life in the lower Tertiary beds. It has been suggested that the underlying Cretaceous beds are the source, but the preponderance of evidence does not support this view. Production from the gas area commenced in September, 1929. Insufficient gas has been run to date to make possible accurate estimates on the life of wells and total reserves.

Identity of the Northwest Colorado Pocket Mouse

Identity of the Northwest Colorado Pocket Mouse