Northwestern Colorado Research Articles

The Desert Shrew, Notiosorex crawfordi (Coues), from Northwestern Colorado

The Desert Shrew, Notiosorex crawfordi (Coues), from Northwestern Colorado

Geomorphic implications of Pre-Wisconsin soils on the White River Plateau erosion surface of northwestern Colorado

The White River Plateau erosion surface (Miocene-Pliocene) at an elevation of approximately 2850 m (9500 ft) is dominated by weakly developed Holocene soils which commonly possess simple A-C horizonation. However, Pre-Wisconsin soils occur on the surface in isolated areas at both high and low topographic sites, most notably in Triangle Park. These Pre-Wisconsin soils consist of composite, polygenetic profiles having truncated, clayey subsoils which are overlain by stone or pebble lines, colluvium, soil creep, and probable local eolian deposits Truncation of the paleosols preceded development of the Holocene soils, which have formed on bedrock surfaces and have been superposed on the truncated, buried paleosols Soil distribution and character, in relation to structure of bedrock on the erosion surface, indicate that the surface as it now exists is structurally controlled and has a topography generated in late Tertiary to Pre-Wisconsin time.

Developments in Eastern and Northwestern Colorado in 1976

The number of exploratory and development wells drilled in eastern and northwestern Colorado in 1976 decreased 13.8% from 1975, whereas the success rate increased from 52.6% in 1975 to 57.8% in 1976. Exploratory drilling was down 14.6% and development drilling was down 13.4%. The only increase in activity over last year was exploratory drilling in northwestern Colorado (14.8%). Development drilling was concentrated in Weld County again this year, primarily in Spindle field. During 1976, 994 wells were drilled, of which 402 were successful oil completions and 173 were successful gas completions.

Foods of Elk and Other Ungulates at Low Elevations in Northwestern Colorado

In northwestern Colorado on areas where elk (Cervus canadenzis) and wild horses have been increasing in recent years, the diets of elk, cattle and wild horses consisted mainly of sedges and grasses. On the same areas mule deer (Odocoileus hemionus) have been decreasing steadily recently, and their diets were mostly browse. The foods of elk, wild horses, and cattle were much more similar to each other than any one of the herbivore diets was to that of mule deer. Cattle and wild horses have strikingly similar diets, and if forage was limited they would compete strongly for forage. There appears to be no large herbivore on the study areas that competes significantly for foods with mule deer. J. WILDL. MANAGE. 41(1):76-80 During the past 30 years elk in Colorado have been increasing slowly. During the past 15 years mule deer have declined rapidly. Record high numbers (23,946) of elk and near record low (46,666) deer numbers were harvested in 1974 (Riffel 1975:1). According to the most recent summary for 1975, the deer harvest was 14 percent less in 1975 than in 1974 (Lashnits 1975:1). In some low elevational ranges in northwestern Colorado, nonmigratory herds of elk have become established where they are not legally hunted or where only a few hunting permits are issued. Some of these same ranges also have increasing herds of wild horses (Cook 1975). There is growing concern for multiple use management of rangelands, and information pertaining to foods shared among different herbivores using a particular range is relatively limited. When provided protection from predators and man, large herbivores not only tolerate but may thrive within broad limits of climate, soil, topography, and vegetation. The food habits of large herbivores are generalized. Precise predictions of the botanical composition of diets of a species of herbivore may differ significantly between areas occurring wit in the same vegetation type. The purpose of this study was to determine the botanical composition of the diets of elk, mule de , wild horses, and cattle on the same

Biostratigraphic Correlation of Mesaverde Group in Southwestern Wyoming and Northwestern Colorado: ABSTRACT

Biostratigraphic Correlation of Mesaverde Group in Southwestern Wyoming and Northwestern Colorado: ABSTRACT

Geology and Shale-Oil Resources of White River-Gray Hills Area, Piceance Creek Basin, Northwestern Colorado: ABSTRACT

Geology and Shale-Oil Resources of White River-Gray Hills Area, Piceance Creek Basin, Northwestern Colorado: ABSTRACT

Improving Gambel Oak Ranges for Elk and Mule Deer by Spraying with 2,4,5-TP

Highlight: Areas of Gambel oak vegetation in northwestern Colorado were sprayed with 2,4,5-TP to evaluate effects on plant abundance and deer and elk use 2 and 5 years after treatment. Grasses increased in abundance 44% after 2 years; shrubs and forbs decreased 29 and 15%, respectively. After 5 years, grasses and shrubs were 17 and 7% , respectively, above pretreatment levels of abundance; forbs were 4% below. Total vegetation on the treated area decreased 4% after 2 years, while a 5% increase was recorded after 5 years. Elk and deer use on the sprayed area increased 73 and 16%, respectively, 2 years after spraying. After 5 years elk use was 11% above pretreatment levels and deer use was 21% below. If 2,4,5-TP is used to spray Gambel oak to modify plant composition and increase elk or deer use, the area should be resprayed at 3-year intervals, indefinitely, if the improved situation is to be maintained.

Terraces of Douglas Creek, northwestern Colorado: An example of episodic erosion

Channel incision began after 1880 in Douglas Creek, a tributary of the White River in northwestern Colorado. This modern erosion produced a complex series of discontinuous, unpaired terraces below the 1880 valley floor. As many as four of these surfaces were formed below the level of the old valley floor by a process of discontinuous downcutting that apparently was not related to changes of base level, climate, or land use, although the initial incision was probably due to the introduction of large numbers of livestock. The progress of incision was impeded as large quantities of sediment were flushed from steep tributary valleys into the main channel. Temporary storage and flushing of the sediment by episodic erosion produced a complex post-1900 terrace sequence. This phenomenon may be expected following rejuvenation of areas of high relief and high sediment production, and episodic incision may be a normal part of the erosional evolution of such areas.

Sorption of SO2on Ground Nahcolite Ore

Large quantities of nahcolite ore, a naturally occurring mineral containing between 70 and 90% sodium bicarbonate are known to occur in the Green River Formation of the Piceance Creek Basin of northwestern Colorado.1 Deposits occur in two major forms, as either bedded or disseminated ore. In the latter case, the host rock is oil shale, a dolomitic marlstone containing kerogen material. Bench and pilot scale studies have shown finely divided nahcolite ore to be an effective SO2 sorbent in baghouse filters.2 These studies form the basis of the nahcolite ore injection process as a means for controlling SO2 emissions to the environment.3 Although there have been published investigations of reactions of SO2 with Na2CO3and NaHCO3, 4 no reference could be found to a systematic study of nahcolite ore reacting with SO2.

Modeling of Noncontinuous Fort Union and Mesaverde Sandstone Reservoirs, Piceance Basin, Northwestern Colorado

Abstract A recent Federal Power Commission study indicated up to 600 trillion ft of natural gas in place in the Rocky Mountains in low-permeability place in the Rocky Mountains in low-permeability Cretaceous and Tertiary nonmarine sandstones. This type of reservoir rock bas been studied in the surface and subsurface in the Piceance Basin area of northwestern Colorado. The sandstone geometry and orientation are characterized in this paper. A "random intersection" technique is developed that uses the geological information to generate a spectrum of reservoir models that may be used to simulate the performance of conventional as well as hydraulically and nuclearly fractured wells. Example reservoir models for fractured wells are compared with reservoir models for nonfractured wells. In general, point-bar sandstones can be simulated by radial models and channel-fill sandstones by linear models. In a sequence of channel-fill sandstones with Piceance Basin geometry, an average well will be Piceance Basin geometry, an average well will be connected to about 18 percent of the in-place reservoir volume in a 320-acre area. Connected reservoir volumes of greater than 70 percent in a 320-acre area are calculated for fractured wells with fracture wing dimensions of 2,000 ft, with actual values depending on fracture extent and pervasiveness. The percent of connected reservoir pervasiveness. The percent of connected reservoir volume decreases as well spacing increases. Introduction Selecting an appropriate model for reservoir simulation can be a difficult task, especially if a minimum amount of subsurface data are available. In many areas, the reservoir rock outcrops within a reasonable distance of the field. Thus, the meager subsurface data can be supplemented by outcrop studies. This paper briefly summarizes the results of outcrop studies on the Mesaverde and Fort Union formations in northwestern Colorado and presents an evaluation of some reservoir models generated by using the outcrop information. This study was an attempt to use all available information sources to supplement the usual subsurface data. It is recommended that data from studies of rock types and geometries be used to help develop that best reservoir model possible; otherwise, important information is being ignored. SUMMARY OF GEOLOGY GEOLOGICAL SETTING The Piceance Basin is located in northwestern Colorado. The basin is a large structural downwarp with a sedimentary sequence more than 20,000 ft thick. The principal gas-bearing units are a series of fluvial Tertiary and Cretaceous sandstone lenses in the Fort Union and Mesaverde formations. A schematic section of the horizons encountered in the Project Rio Blanco area is presented in Fig. 1. A more comprehensive geological description is presented in Appendix A. presented in Appendix A. SUMMARY OF OUTCROP STUDY The Fort Union-Mesaverde sandstone bodies studied in outcrops along the periphery of the northern Piceance Basin appear to be predominately fluvial channel-fill deposits with some point-bar sandstones. The point-bar sandstones occur in the lower Fort Union section. The most commonly observed thickness was between 20 and 30 ft (manly channel-fill sandstones) and the log mean length/thickness ratio (L/h) was 35 for all of the observed sandstones lenses, with a minimum of about 19/1 and a maximum of about 140/1. Length/width (L/W) ratios (shape of body in plan view) average 2-4/1 for the Fort Union point-bar sandstones) and greater than 10/1 for the Mesaverde channel-fill sandstones (Appendix B). Average length/width/thickness (L/W/h) ratios are the following. Sandstone Formation Type L/W/h Fort Union Point-bar 190/90/1(Typical Case) - (7,600/3,200/40 ft) Mesaverde Channel-fill 140/14/1(Typical Case) − (3,500/350/25 ft) SPEJ P. 175

Developments in Eastern and Northwestern Colorado

Developments in Eastern and Northwestern Colorado

Oil Shale Development: Status and Prospects

Technology is available for commercial development of the vast U.S. oil shale deposits. However, economic changes and uncertainties, including inflation in construction costs, impede this development. If economic incentives are provided for construction of pioneer oil shale plants, oil shale production could reach 2 million BID in 1995. Introduction This paper concerns oil shale, specifically the status of oil shale development and the contribution that oil shale can be expected to make to the nation's energy supply during the next 20 years. The subject is timely because the United States needs oil, and the oil shale deposits of the U.S. constitute the world's largest known hydrocarbon reserve. Oil Shale Reserves The prime oil shale deposits of the U.S. are in northwestern Colorado, eastern Utah, and southern Wyoming. The largest deposit in this region is in a 1,200-sq mile area of northwestern Colorado referred to as the Piceance Basin. Piceance Basin. The oil shale deposit of the Piceance Basin has been extensively explored and the results in terms of potential oil in place are staggering. The 1,200-sq mile area potential oil in place are staggering. The 1,200-sq mile area is underlain by a rich oil-shale bed referred to as the Mahogany Zone. The bed is from 75 to 250 ft thick, and the in-place oil content is projected to be 164 billion bbl. Below the Mahogany Zone and separated by lowergrade materials are two other rich zones. The total content of the three rich zones is 320 billion bbl. In the three-state area, and counting shale in leaner beds, the total estimated in-place resource is 1.8 trillion bbl. For this discussion, it is not important what specific reserve estimate is considered, for it is clear that the reserves are more than enough to make a vast contribution to the nation's energy supply. For example, the Mahogany Zone in-place reserve of the Piceance Basin is many times larger than the proven Piceance Basin is many times larger than the proven conventional petroleum reserves of the U.S.; and the reserves of the three rich zones of the Piceance Basin approach in magnitude the proven reserves of all the Middle East. Oil Shale Recovery Processes All work on oil shale recovery has focused on heating the shale to recover the contained oil and gas, for there is no other practical method for extracting a significant portion of the contained oil. In the processes studied, portion of the contained oil. In the processes studied, the shale is heated to about 900 degrees F, at which temperature the organic material in shale rapidly decomposes into oil vapor and gas. Cooling this vapor stream produces liquid oil and uncondensed, light hydrocarbon produces liquid oil and uncondensed, light hydrocarbon gases. Surface Retorting Processes Most development work on oil shale recovery has been directed to mining the shale, bringing it to the surface, and then processing it in surface facilities. The various surface retorting processes can be classified according to the method used to provide heat for the retorting reaction. With one procedure, the gas combustion process, the source of heat is internal combustion within the retorting vessel, and a controlled amount of air is admitted to the retort to supply oxygen for the combustion reaction. JPT P. 16

Limnological characteristics of strip mine ponds in northwestern Colorado, U. S. A.

Limnological characteristics of strip mine ponds in northwestern Colorado, U. S. A.

Developments in Eastern and Northwestern Colorado in 1974

Exploratory and development wells drilled in eastern and northwestern Colorado in 1974 were up 17% from 1973; the success ratio increased from 42.6% in 1973 to 50.9% in 1974. Exploratory drilling was down 15.4%, but development drilling increased 65.2%. During 1974, 323 exploratory tests were drilled in Colorado and, of these, 25 found oil and 24 found gas. Development drilling was accelerated in all of Colorado but was most concentrated in the western Denver basin in the Wattenberg, Spindle, Surrey, and Third Creek fields. A decrease in both development and exploratory drilling is expected in 1975.

Gully Erosion, Northwestern Colorado: A Threshold Phenomenon

The widespread occurrence of discontinuous gullies in the oil-shale region of northwestern Colorado is of particular concern because of the resulting progressive destruction of the valley floors. Furthermore, the integration of a semi-arid drainage network can cause a rapid increase in the sediment yield of the basin, with subsequent harmful effects downstream. Field work in the Piceance Creek and Yellow Creek drainage basins indicates that these discontinuous gullies developed on oversteepened segments of the valley floors. Although the critical slope of entrenchment is probably related to magnitude of run-off, discharge measurements are not available; therefore, drainage-basin area was selected as the most representative measure of discharge. An inverse relation between drainage-basin area and critical slope of entrenchment applies, and the lower limit of scatter of the data establishes a critical slope-area relation, which can be used to identify potentially unstable valley floors. This relation can help the land manager determine areas of instability where preventive measures can most economically and successfully be undertaken. It is stressed that this particular quantitative relation is applicable only to the Piceance Creek and Yellow Creek drainage basins. In more heterogeneous basins, other variables will need to be included in the analysis; however, the general theory of valley stability will remain applicable.

Recent Records of Birds from the Yampa Valley, Northwestern Colorado

Recent Records of Birds from the Yampa Valley, Northwestern Colorado

Developments in Eastern and Northwestern Colorado, 1973

Exploratory and development wells drilled in eastern and northwestern Colorado in 1973 were down 31% from 1972, but the success ratio remained essentially the same. Exploratory drilling was down 8.2% whereas development drilling decreased 47.8%. An overall decrease in drilling activity in the Denver basin is the primary reason for the reduction in total drilling activities. During 1973, 382 exploratory tests were drilled in Colorado and, of these, 27 found oil and 29 found gas. Development drilling was highlighted by extensive development programs in the Wattenberg, Spindle, Surrey, and Singletree oil and gas fields and a strong infield program in Rangely field. An increase in development and exploratory drilling is anticipated for 1974.

Current Status of Oil Shale Development in United States: ABSTRACT

There is no commercial oil shale development in the United States today despite extensive and well known deposits and periodic flurries of interest. In the current energy situation the oil shales of the Green River Formation in Colorado, Utah, and Wyoming are attracting a great deal of interest as a possible secure domestic source of synthetic crude oil. High grade oil shale deposits containing a potential 600 billion bbl of shale oil occur in an 11-million-acre area of the three states. The tempo of predevelopment activity has accelerated during the last year and the prospects for a domestic shale oil industry in the foreseeable future appear good. Four private industrial groups recently have announced tentative plans for development of private oil shale lands in Colorado. The Colony Development group has operated a semi-works scale facility north of Grand Valley, Colorado, at 1,000 tons per day with room and pillar underground mining techniques and a surface retort using the TOSCO II system. Union Oil Company has done prior experimental mining and retorting on their lands which adjoin the Colony property. Superior Oil Company has announced their intention to explore the lower oil shale zones by an inclined shaft to determine the feasibility of a multi-mineral development producing nahcolite and dawsonite as well as shale oil in the northern part of the Piceance basin. Occidental Petroleum Company has successfully operated an ex erimental in-situ retorting process north of DeBeque, Colorado. A group of 16 companies has joined in a 30-month program to develop and test a new retorting system. The United States Department of Interior has been involved in research and investigation of the Green River oil shales and the technology for their development for many years. It has now initiated a prototype program of leasing for development by private End_Page 905------------------------------ industry of a small part of the approximately 80% of the oil shale resources which are Federally owned. Four years of study and planning and the completion of a six-volume Environmental Impact Statement have preceded this action. If this program is successful the production from the six Federal leases combined with production from private lands could reach an estimated 400,000 bbl per day by the early 1980s and one million bbl per day before the close of that decade. The first lease offering under the prototype program of a single 5,100-acre tract in northwestern Colorado was on January 8, 1974. Eight offers were received with a high bid of $210,305,600 submitted by a combination of Standard Oil Company of Indiana and the Gulf Oil Corporation. This appears to be the highest per acre bid ever received by the Federal government for the leasing of any mineral deposit. The total of all bonus bids received was $641,126,463.09. End_of_Article - Last_Page 906------------

Petrology of the Cutler Formation (Pennsylvanian-Permian) Near Gateway, Colorado, and Fisher Towers, Utah

ABSTRACT The Cutler Formation (Pennsylvanian-Permian) of the northwestern Colorado Plateau was deposited as an alluvial fan complex along the western margin of the ancestral Uncompahgre Uplift. Near Gateway, Colorado, and Fisher Towers, Utah, the Cutler comprises rapidly-deposited, poorly-sorted, conglomeratic sandstone and siltstone. During deposition, the climate was arid to semi-arid. The red color of the Cutler rocks resulted from the formation of hematite by intrastratal solution of iron-bearing minerals. The detritus at the Gateway section differs in mineral composition and texture from the Fisher Towers section. The Gateway section is characterized by an overall coarse grain size, a high potassium feldspar to total feldspar ratio, and a non-micaceous, non-opaque heavy-mineral assemblage rich in epidote, sphene, and garnet. The Fisher Towers section is finer grained, contains more quartz, and has a heavy-mineral assemblage dominated by garnet, sillimanite, and tourmaline, with rare epidote and sphene. These differences in mineralogy reflect regional difference in provenance. The source rocks for the Gateway section were largely Precambrian Vernal Mesa-type quartz monzonite and gneisses. At Fisher Towers, gneiss was the main source rock.

Absolute stress measurements at the rangely anticline, Northwestern Colorado: Discussion of R. V. De La Cruz and C. B. Raleigh's

Absolute stress measurements at the rangely anticline, Northwestern Colorado: Discussion of R. V. De La Cruz and C. B. Raleigh's