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Source-linked reports with geographic coverage including Colorado.

At least 1,189 records · Page 66Linked to original sources
USGS1996

Recurrent eruption and subsidence at the Platoro caldera complex, southeastern San Juan volcanic field, Colorado: New tales from old tuffs

Reinterpretation of a voluminous regional ash-flow sheet (Masonic Park Tuff) as two separate tuff sheets of similar phenocryst-rich dacite erupted from separate source calderas has important implications for evolution of the multicyclic Platoro caldera complex and for caldera-forming processes generally. Masonic Park Tuff in central parts of the San Juan field, including the type area, was erupted from a concealed source at 28.6 Ma, but widespread tuff previously mapped as Masonic Park Tuff in the southeastern San Juan Mountains is the product of the youngest large-volume eruption of the Platoro caldera complex at 28.4 Ma. This large unit, newly named the “Chiquito Peak Tuff,” is the last-erupted tuff of the Treasure Mountain Group, which consists of at least 20 separate ash-flow sheets of dacite to low-silica rhyolite erupted from the Platoro complex during a 1 m.y. interval (29.5−28.4 Ma). Two Treasure Mountain tuff sheets have volumes in excess of 1000 km 3 each, and five more have volumes of 50–150 km 3 . The total volume of ash-flow tuff exceeds 2500 km 3 , and caldera-related lavas of dominantly andesitic composition make up 250-500 km 3 more. A much greater volume of intermediate-composition magma must have solidified in subcaldera magma chambers. Most preserved features of the Platoro complex-including postcollapse asymmetrical trap-door resurgent uplift of the ponded intracaldera tuff and concurrent infilling by andesitic lava flows-postdate eruption of the Chiquito Peak Tuff. The numerous large-volume pre-Chiquito Peak ash-flow tuffs document multiple eruptions accompanied by recurrent subsidence; early-formed caldera walls nearly coincide with margins of the later Chiquito Peak collapse. Repeated syneruptive collapse at the Platoro complex requires cumulative subsidence of at least 10 km. The rapid regeneration of silicic magmas requires the sustained presence of an andesitic subcaldera magma reservoir, or its rapid replenishment, during the 1 m.y. life span of the Platoro complex. Either case implies large-scale stoping and assimilative recycling of the Tertiary section, including intracaldera tuffs.

Colorado↗
USGS1996

Climatic significance of the bristlecone pine latewood frost-ring record at Almagre Mountain, Colorado, U.S.A.

From 1900 to 1993, latewood frost rings occurred in 1903, 1912, 1941, 1961, and 1965 in 10 to 21% of the sampled bristlecone pines at Almagre Mountain, Colorado. In early to mid September in each of those years, a severe outbreak of unseasonably cold air from higher latitudes produced a memorable or historic late-summer snowstorm in the western United States. Record subfreezing temperatures during these snowstorms probably caused the latewood frost rings, shortened (by about 1 mo in 1912) already colder than normal growing seasons, and caused crop damage in parts of the Western United States. Latewood frost rings recorded in relatively high percentages of the sampled trees (such as the 1805 event in 61% of sampled trees) were probably caused by multiple severe outbreaks of unseasonably cold air from higher latitudes that occurred from early September (possibly as early as mid- or late August) to mid-September. Analyses of 1900-1992 temperature data for two widely separated Colorado stations, Fort Collins and Colorado Springs, show that average summer (June-September) temperatures during latewood frost-ring years in this century were 1.5 and 2.0°C cooler than normal, respectively. Mountain snowpack probably persisted through these cool summers and was subsequently buried by the earlier than normal snowfall in September. Latewood frost-ring, ring-width, historical, and other data suggest that severe to cataclysmic volcanic eruptions from 1812 to 1835 triggered (1) an extended period of climatic cooling from as early as 1816 or 1817 through the early 1850s in the Southern Rocky Mountains, (2) catastrophic winters in Colorado and Wyoming in 1842-43 and 1844-45, and in the Great Salt Lake Basin in 1836-37, that caused large-scale destruction of bison and other large plains animals, and (3) Little Ice Age alpine glacial advances in about 1850-60 in the western United States.

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USGS1996

What affects water quality in the Upper Colorado River basin?

The Upper Colorado River Basin is 1 of 60 study units selected for water-quality assessment by the U.S. Geological Survey as part of the National Water-Quality Assessment program. Understanding the environmental setting of the Upper Colorado River Basin study unit is important in evaluating water-quality issues in the basin. Information about the environmental setting identifies the basin characteristics and includes natural and human factors that affect the physical, chemical, and biological quality of water in the basin. This information has been used to design surface-water- and ground-water-quality sampling networks in the basin to assess overall water quality of the basin

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USGS1996

Salinity in the Colorado River in the Grand Valley, western Colorado, 1994-95

Salinity, or the dissolved-solids concentration, is the measure of salts such as sodium chloride, calcium bicarbonate, and calcium sulfate that are dissolved in water. About one-half of the salinity in the Colorado River Basin is from natural sources (U.S. Department of the Interior, 1995), such as thermal springs in the Glenwood-Dotsero area, located about 90 miles upstream from Grand Junction (fig. 1). Effects of human activities, such as irrigation, reservoir evaporation, and transbasin diversions, have increased the levels of salinity in the Colorado River. High salinity can affect industrial and municipal water users by causing increased water-treatment costs, increased deterioration of plumbing and appliances, increased soap needs, and undesirable taste of drinking water. High salinity also can cause lower crop yields by reducing water and nutrient uptake by plants and can increase agricultural production costs because of higher leaching and drainage requirements. Agricultural losses might occur when salinity reaches about 700?850 milligrams per liter (U.S Department of the Interior, 1994). Figure 1. Irrigated area in the Grand Valley and locations of sampling sites for the 1994?95 salinity study of the Colorado River. The Colorado River is the major source of irrigation water to the Grand Valley (fig. 1) and also is one source of water for the Clifton Water District, which supplies domestic water to part of the eastern Grand Valley. During spring and early summer in 1994, the Colorado River in the Grand Valley had lower than average streamflow. There was concern by water users about the effect of this low streamflow on salinity in the river. In 1994, the U.S. Geological Survey (USGS), in cooperation with the Colorado River Water Conservation District, began a study to evaluate salinity in the Colorado River. This fact sheet describes results of that study. The specific objectives of the fact sheet are to (1) compare salinity in the Colorado River among different locations from Cameo to the Colorado-Utah State line, (2) assess variations in salinity for different times of the year, and (3) describe the relation between streamflow and salinity in the river.

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USGS1996

Water-quality data for the Arkansas River Basin, southeastern Colorado, 1990-93

Water-quality data were collected and compiled for 59 surface-water stations in the Arkansas River Basin of Colorado. The purpose of the data collection was to describe selected water-quality characteristics of the Arkansas River from the headwaters downstream to the Colorado-Kansas State line. Data are presented for 19 Arkansas River stations, 31 tributary stations, 2 mine-drainage stations, and 7 transmountain diversion stations. Water-quality data presented in this report include instantaneous discharge; onsite measurements of specific conductance, pH, water temperature, and dissolved oxygen; analytical concentrations of bacteria, dissolved solids, major nutrients, trace elements, pesticides, radiochemicals, and suspended sediment; and quality-assurance data for selected water-quality constituents. Sampling began in April 1990 and continued through March 1993 at the 59 surface-water stations. The basinwide water-quality study was initiated in 1988 by the U.S. Geological Survey in cooperation with 14 local agencies and the Bureau of Reclamation.

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USGS1996

Hydrogeology of the alluvial aquifers at the Pueblo Depot Activity near Pueblo, Colorado

In 1992, the U.S. Army Corps of Engineers and the U.S. Army Pueblo Depot Activity requested that the U.S. Geological Survey study the hydrogeology of the Pueblo Depot Activity, a 36-square-mile facility that has been operated by the U.S. Army since 1942. The purpose of the study was to provide an updated hydrogcological framework to facilitate the investigation of specific sites on the facility that might require remediation. This report describes the hydrogeology of the alluvial aquifers beneath the facility and the distribution of specific conductance of ground water in those aquifers. The Pueblo Depot Activity is underlain by two alluvial aquifers: (1) The terrace alluvial aquifer, which is a southernmost, downgradicnt part of an erosional remnant of an extensive terrace deposit; and (2) the Chico Creek alluvial aquifer, a smaller alluvial system along Chico Creek. These aquifers primarily consist of sand separated by clay layers and are underlain by the almost impermeable Pierre Shale of Upper Cretaceous age. The bedrock surface, which has an average slope of 28 feet per mile to the south-southeast, is relatively regular beneath the northern two-thirds of the terrace deposits at the Pueblo Depot Activity, but forms an irregular surface of troughs, hills, and ridges in the southwestern part of the terrace alluvium. Saturated thickness of the terrace aquifer ranges from 0 to about 45 feet. The bedrock surface beneath the Chico Creek aquifer slopes about 31 feet per mile to the south. Saturated thickness of the Chico Creek alluvium ranges from 0 to about 30 ft, but generally is less than 15 ft. Total thickness of the Chico Creek alluvium in the saturated area ranges from 16 to 41 ft. Water in the terrace alluvial aquifer generally flows southward, except in the southwestern part where directions of flow are complex. Measured hydraulic conductivity ranges from 0.4 to 400 feet per day (median 26 feet per day). Estimates for vertically averaged ground-water-flow velocity range from 0.02 to 3 feet per day (median 0.9 foot per day). Water in the Chico Creek alluvial aquifer generally flows southward to the Arkansas River alluvium. Measured hydraulic conductivity ranges from 14 to 310 feet per day (median 42 feet per day). Estimates for vertically averaged ground water-flow velocity range from 0.5 to 4 feet per day (median 0.7 foot per day). Specific conductance of ground water in the terrace alluvial aquifer generally is less than 800 microsiemens per centimeter; the smallest values were observed in the north-central part of the Pueblo Depot Activity. In the southwestern part of the terrace alluvial aquifer, values varied in an irregular pattern, and values as large as 3,300 microsiemens per centimeter were measured locally. Water in the terrace alluvial aquifer was dominated by the sodium cation and usually by the bicarbonate anion, and sulfate usually was present in substantial (and locally predominant) concentrations. Measured specific conductance of water in the Chico Creek alluvial aquifer ranged from 683 to 1,460 microsiemens per centimeter. This water was dominated by the sodium cation and by the bicarbonate and sulfate anions; sulfate was more predominant to the south.

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USGS1996

Trend analysis of selected water-quality data associated with salinity-control projects in the Grand Valley, in the lower Gunnison River basin, and at Meeker Dome, western Colorado

To decrease salt loading to the Colorado River from irrigated agriculture, salinity-control projects have been under construction since 1979 by the Bureau of Reclamation and the U.S. Department of Agriculture in the Grand Valley and since 1988 in the lower Gunnison River Basin of western Colorado. In 1980, a salinity-control project was initiated at Meeker Dome, which involved plugging three abandoned oil wells that were discharging saline water to the White River. Trend analysis was used to determine if the salinity-control projects had affected salinity in the Colorado and White Rivers. The mean annual dissolved-solids load in the Colorado River near the Colorado-Utah State line for water years 1970-93 was about 3.32 million tons. About 46 percent of that load was from the Colorado River upstream from the Grand Valley and about 38 percent was from the Gunnison River. About 16 percent of the dissolved-solids load in the Colorado River near the State line was discharged from the Grand Valley, and most of the Grand Valley dissolved-solids load was from irrigation-induced sources. Monotonic trend analysis of dissolved-solids and major-ion data for the Colorado and Gunnison Rivers was used for determining if salinity-control projects had affected salinity (dissolved solids) in the Colorado River. Data collected in water years 1970-93 at gaging stations on the Colorado River-one near Cameo and the other near the Colorado-Utah State line, and at the station on the Gunnison River near Grand Junction-were analyzed for trends. A computerized procedure developed by the U.S. Geological Survey that uses the nonparametric seasonal Kendall test with adjustment for streamflow was used for trend analysis of periodic and monthly data, and linear regression was used for trend analysis of annual data. Three time periods were tested, including periods that were concurrent with work on salinity-control projects. Many of the trends in unadjusted concentration and load data were not statistically significant. There were downward trends in flow-adjusted dissolved-solids and major-ion concentrations and in monthly dissolved-solids loads for all three stations in the 1970's, prior to the salinity-control projects. The two stations on the Colorado River also had significant downward trends in flow-adjusted concentrations and loads for water years 1986-93. The cumulative effects of salinity-control projects in the Grand Valley and in the lower Gunnison River Basin on salinity in the Colorado River would have become more substantial after the mid-1980's. Part of the decrease in dissolved solids in the Colorado River near the State line probably was related to salinity-control projects; however, there apparently are other factors that are affecting dissolved solids in the upper Colorado River in addition to salinity-control projects. A significant decrease in chloride and sodium concentrations in the White River downstream from Meeker Dome indicated that the well plugging in 1981 was successful in stopping much of the discharge of saline water from the wells. Chloride and sodium concentrations have not changed in the White River at Meeker or downstream from Meeker during water years 1982-95, indicating that the well plugging has remained intact.

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USGS1996

Water-quality assessment of the Rio Grande Valley, Colorado, New Mexico, and Texas: Shallow ground-water quality of a land-use area in the San Luis Valley, south-central Colorado, 1993

This report describes the quality of shallow ground water in an agricultural area in the San Luis Valley, Colorado, and discusses how natural and human factors affect the quality of shallow ground water. Thirty-five wells were installed, and water samples were collected from these wells and analyzed for selected dissolved common constituents, nutrients, trace elements, radionuclides, and synthetic organic compounds. The San Luis Valley is a high intermontane valley that is partially drained by the Rio Grande. The San Luis Valley land-use study area was limited to a part of the valley where the depth to water is generally less than 25 feet. The area where the 35 monitor wells were installed was further limited to the part of the study area where center-pivot overhead sprinklers are used to irrigate crops. Precipitation, runoff from adjacent mountainous areas, and ground-water inflow from the adjacent mountainous areas are the main sources of water to the aquifers in the San Luis Valley. Discharge of water from the shallow, unconfined aquifer in the valley is mainly from evapotranspiration. The dominant land use in the San Luis Valley is agriculture, although nonirrigated land and residential land are interspersed with agricultural land. Alfalfa, native hay, barley, wheat, potatoes, and other vegetables are the main crops. Dissolved-solids concentrations in shallow ground water sampled ranged from 75 to 1,960 milligrams per liter. The largest median concentration of cations was for calcium, and the largest median concentration of anions was for bicarbonate in shallow ground water in the San Luis Valley. Calcium concentrations ranged from 7.5 to 300 milligrams per liter, and bicarbonate concentrations ranged from 28 to 451 milligrams per liter. Nitrite plus nitrate concentrations ranged from less than 0.1 to 58 milligrams per liter as N; water from 11 wells had nitrite plus nitrate concentrations greater than 10 milligrams per liter as N. With the exception of the following trace elements--aluminum, barium, iron, manganese, molybdenum, and uranium--the concentrations of trace elements were less than 10 micrograms per liter in 90 percent of the samples. All trace-element concentrations measured were below the maximum contaminant levels set by the U.S. Environmental Protection Agency. Five samples exceeded the proposed maximum contaminant level of 0.02 milligram per liter for uranium. All samples collected exceeded the proposed maximum contaminant level for radon-222. The volatile organic compound methyltertbutylether was detected in one sample at a concentration of 0.6 microgram per liter. Of the pesticides analyzed for, one or more were detected in water from 5 of the 35 wells sampled. Metribuzin was the most commonly detected pesticide and was detected in water from three wells at concentrations ranging from an estimated 0.005 to 0.017 microgram per liter. Metolachlor (detected in one sample at a concentration of 0.072 microgram per liter), prometon (detected in one sample at a concentration of 0.01 microgram per liter), and p,p'-DDE (detected in one sample at an estimated concentration of 0.002 microgram per liter) were the other pesticides detected. The U.S. Environmental Protection Agency lifetime health advisory for metolachlor, metribuzin, and prometon is 100 micrograms per liter, which is much larger than the concentrations measured in the shallow ground water sampled for this study. The elevated nitrite plus nitrate concentrations in shallow ground water are indicative of leaching of fertilizers from the land surface. This conclusion is consistent with conclusions made in other investigations of the San Luis Valley.

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