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Research about Pima County, Arizona

Source-linked reports with geographic coverage including Pima County, Arizona.

At least 19 recordsLinked to original sources
USGS2007

Estimated infiltration, percolation, and recharge rates at the Rillito Creek focused recharge investigation site, Pima County, Arizona

A large fraction of ground water stored in the alluvial aquifers in the Southwest is recharged by water that percolates through ephemeral stream-channel deposits. The amount of water currently recharging many of these aquifers is insufficient to meet current and future demands. Improving the understanding of streambed infiltration and the subsequent redistribution of water within the unsaturated zone is fundamental to quantifying and forming an accurate description of streambed recharge. In addition, improved estimates of recharge from ephemeral-stream channels will reduce uncertainties in water-budget components used in current ground-water models. This chapter presents a summary of findings related to a focused recharge investigation along Rillito Creek in Tucson, Arizona. A variety of approaches used to estimate infiltration, percolation, and recharge fluxes are presented that provide a wide range of temporal- and spatial-scale measurements of recharge beneath Rillito Creek. The approaches discussed include analyses of (1) cores and cuttings for hydraulic and textural properties, (2) environmental tracers from the water extracted from the cores and cuttings, (3) seepage measurements made during sustained streamflow, (4) heat as a tracer and numerical simulations of the movement of heat through the streambed sediments, (5) water-content variations, (6) water-level responses to streamflow in piezometers within the stream channel, and (7) gravity changes in response to recharge events. Hydraulic properties of the materials underlying Rillito Creek were used to estimate long-term potential recharge rates. Seepage measurements and analyses of temperature and water content were used to estimate infiltration rates, and environmental tracers were used to estimate percolation rates through the thick unsaturated zone. The presence or lack of tritium in the water was used to determine whether or not water in the unsaturated zone infiltrated within the past 40 years. Analysis of water-level and temporal-gravity data were used to estimate recharge volumes. Data presented in this chapter were collected from 1999 though 2002. Precipitation and streamflow during this period were less than the long-term average; however, two periods of significant streamflow resulted in recharge—one in the summer of 1999 and the other in the fall/winter of 2000. Flux estimates of infiltration and recharge vary from less than 0.1 to 1.0 cubic meter per second per kilometer of streamflow. Recharge-flux estimates are larger than infiltration estimates. Larger recharge fluxes than infiltration fluxes are explained by the scale of measurements. Methods used to estimate recharge rates incorporate the largest volumetric and temporal scales and are likely to have fluxes from other nearby sources, such as unmeasured tributaries, whereas the methods used to estimate infiltration incorporate the smallest scales, reflecting infiltration rates at individual measurement sites.

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USGS2006

The Ajo Mining District, Pima County, Arizona: Evidence for middle Cenozoic detachment faulting, plutonism, volcanism, and hydrothermal alteration

Introduction: The Ajo porphyry copper deposit and surrounding Upper Cretaceous rocks have been separated from their plutonic source and rotated by detachment faulting. Overlying middle Cenozoic sedimentary and volcanic rocks have been tilted and show evidence for two periods of rotation. Following these rotations, a granitic stock (23.7?0.2 Ma) intruded basement rocks west of the Ajo deposit. This stock was uplifted 2.5 km to expose deep-seated Na-Ca alteration.

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USGS2005

Effects of drought on shrub survival and longevity in the northern Sonoran Desert

Effects of drought on shrub survival and longevity in the northern Sonoran Desert. J. Torrey Bot. Soc. 132: 421–431. 2005.—Permanent vegetation plots in the northern Sonoran Desert, USA, provided an opportunity to assess the effects of recent drought on desert shrubs and to examine survival in relation to rainfall variability during the past 76 years. Survival and maximum longevity of six species were determined for eight intercensus periods between 1928 and 2004. Average annual survival was Ambrosia deltoidea , 0.9167 ± 0.0415; Encelia farinosa , 0.7952 ± 0.0926; Janusia gracilis , 0.9334 ± 0.0247; Krameria grayi , 0.9702 ± 0.0270; Larrea tridentata , 0.9861 ± 0.0174; and Lycium berlandieri , 0.9910 ± 0.0077. The longest-lived species were Larrea , Lycium , and Krameria , with average maximum life spans of 330, 211, and 184 years. Janusia , Ambrosia , and Encelia were much shorter lived, with average maximum longevity of 53, 40, and 16 years. Winter rain equalled or exceeded 90% of the long-term average accumulation except during 1948 to 1959 (65% of average) and from 2001 to 2003 (49% of average). Summer rain did not drop below 90% of the average accumulation in any period. The 1950s drought caused modest declines in survival of Ambrosia , Encelia , Janusia , Krameria , and Lycium . The effects of the recent drought were much more pronounced, resulting in sharp declines in survival and maximum longevity of Ambrosia , Encelia , Krameria , and Larrea , and modest declines for Lycium . Despite heightened mortality during the recent severe drought, 72% of the deaths observed between 1928 and 2004 occurred during periods of average or better-than-average rain, providing support for the idea that demography of shrubs in arid regions is influenced by continuous as well as episodic processes.

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USGS2002

Distance sampling for Sonoran Desert tortoises

We used line transects and distance sampling in combination with radiotelemetry to estimate density of a desert tortoise (Gopherus agassizii) population in the Rincon Mountains near Tucson, Arizona, USA, as part of a long-term study evaluating the impact of urban development on tortoises. During 2000, 34 1-km transects were each sampled twice in the 368.5-ha study area. We observed 46 tortoises with midline carapace lengths ???150 mm (subadults and adults) plus 7 juveniles on transects. For subadults and adults, the encounter rate was 0.63 tortoises/km, and the mean proportion of tortoises observable during radiotelemetry, conducted concurrently with transect sampling, was 82%. Corrected mean density based on line transects and radiotelemetry was 0.523 tortoises/ha (CV = 22.99, 95% CI = 0.29-0.79), and absolute abundance in the study area was estimated to be 193 (CV = 23.0%, CI = 107-291). Using the 2 independent coverages of transects as separate samples, the Lincoln-Petersen mark-recapture estimator produced an abundance estimate of 224 subadult and adult tortoises (CV = 53.9%, CI = 72-440). Transects measured on the ground over uneven topography resulted in 3% smaller estimates of density when compared to analysis with transect lengths determined from coordinates plotted on a map. Distance sampling appears to be a feasible method of estimating density of Sonoran Desert populations of the desert tortoise, but transect lengths should be based on mapped rather than measured distances to prevent biases caused by uneven topography.

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USGS2002

Characteristics of shallow deposits beneath Rillito Creek, Pima County, Arizona

Characteristics of the stream-channel and basin-fill deposits beneath a 12-mile reach of Rillito Creek, Pima County, Arizona, were obtained to describe the geohydrologic system. The findings presented here are part of a larger project to improve the understanding of recharge processes beneath ephemeral streams. The stream-channel deposits, which range in thickness from 15 to 40 feet, generally are sandy gravels or gravelly sands. On average, the stream-channel deposits are 44 percent gravel, 51 percent sand, 2 percent silt, and 3 percent clay. The underlying basin-fill deposits also are sandy gravels or gravelly sands but have, on average, a larger component of silt and clay than the stream-channel deposits?about 9 percent silt and 6 percent clay. Porosity values for the stream-channel and basin-fill deposits are similar: about 31 and 34 percent on average, respectively. Volumetric moisture content and percent saturation, however, generally were lower in the stream-channel deposits than in the basin-fill deposits. Moisture content in the stream-channel deposits ranged from 2 to 40 percent and averaged about 18 percent, whereas moisture content in the basin-fill deposits ranged from 7 to 47 percent and averaged about 24 percent. Saturation in the stream-channel deposits ranged from 9 to 100 percent and averaged about 58 percent; saturation in the basin-fill deposits ranged from 30 to 100 percent and averaged about 69 percent. Porosity and moisture content correlate with silt and clay content. Cumulative thickness of water in the 100- to 125-foot thick unsaturated zone obtained by integrating the moisture content over depth, ranged from 17.2 to 40.4 feet. Matric potential for saturation levels at the time of sample collection generally was less than -1 bar for deposits that were less than 35 percent saturated. Matric potential generally was greater than -0.1 bar for deposits that were more than 65 percent saturated. Moisture-retention curves are a function of the physical properties, such as porosity and grain size, of the sediments. The shapes and van Genuchten fitting parameters of moisture-retention curves for the stream-channel deposits are different from those of the basin-fill deposits. For instance, the fitting parameter, a, for stream-channel deposits ranged from 4.56 to 1,220 bar-1 and averaged 220 bar-1, whereas a for basin-fill deposits ranged from 4.22 to 67.9 bar-1 and averaged 22.8 bar-1. The residual water content for the basin-fill deposits is greater than that for the stream-channel deposits. Relative hydraulic conductivity of the stream-channel deposits is less than relative hydraulic conductivity of the basin-fill deposits at the same matric potential. Unsaturated hydraulic conductivity for moisture conditions that existed at the time of sample collection typically was more than two orders of magnitude less than saturated hydraulic conductivity. Saturated vertical hydraulic conductivity of the stream-channel deposits is about an order of magnitude greater than that of the basin-fill deposits. The equivalent hydraulic conductivity of stream-channel deposits ranges from 2 to 7.3 feet per day, and averages about 4 feet per day, whereas the equivalent hydraulic conductivity of the basin-fill deposits ranges from 0.06 to 1.5 feet per day and averages 0.61 foot per day. The equivalent vertical hydraulic conductivity of the entire unsaturated zone cored is 0.75 foot per day. Assuming no vertical to horizontal anisotropy, the equivalent horizontal hydraulic conductivity generally is about two to three times that of the equivalent vertical hydraulic conductivity. The difference between average equivalent vertical and horizontal hydraulic conductivity values results from the differences in methods used to calculate the respective values. Electrical methods were useful in discriminating between stream-channel deposits and basin-fill deposits. In general, electrical conductivity of the stream-channel deposits was less than 30 millimhos per meter and averaged 27 millimhos per meter. The conductivity of the basin-fill deposits was greater than that of the stream-channel deposits and averaged 44 millimhos per meter. The greater conductivity probably is related to factors such as greater moisture content and fraction of fine sediments in the basin-fill deposits. Apparent resistivity measured with two-dimensional resistivity soundings generally decreased with depth. The resistivity values from the near-surface measurements represent dry stream-channel deposits and averaged 303 ohm meters. The resistivity values for basin-fill deposits generally were less than 140 ohm meters and less than 100 ohm meters when saturated. Seismic-velocity values for the recent alluvium (stream-channel and terrace deposits) ranged from 1,150 to 2,200 feet per second, whereas values for basin-fill deposits ranged from 2,000 to 11,650 feet per second. The average seismic velocity for the stream-channel deposits (1,300 feet per second) was less than that for the terrace deposits (1,600 feet per second). Saturated basin-fill deposits had an average velocity of 7,800 feet per second, whereas unsaturated basin-fill deposits had an average velocity of 2,750 feet per second.

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USGS2001

Implications of seed size for seedling survival in Carnegiea gigantea and Ferocactus wislizeni (Cactaceae)

Larger seeds have been shown to convey benefits for seedling survival but the mechanisms of this process are not well understood. In this study, seed size and seedling survival were compared for 2 sympatric cactus species, Carnegiea gigantea (Engelm.) Britt. & Rose and Ferocactus wislizeni (Engelm.) Britt. & Rose, in laboratory and field experiments in the northern Sonoran Desert. Both species have small seeds, but Ferocactus seeds are nearly twice as long and 3 times as heavy as those of Carnegiea . The difference in size is perpetuated after germination: new Ferocactus seedlings have 4 times the estimated volume of new Carnegiea seedlings. In an outdoor experiment, annual survivorship of both species was low but was 6 times higher for Ferocactus (6 seedlings, 8.1%) than Carnegiea (1 seedling, 1.4%). The pattern of seedling mortality in relation to temperature and rain suggests that, after the initial flush of seed and seedling predation, drought and heat took a greater toll on Carnegiea than Ferocactus seedlings, probably because the larger seedling volume of Ferocactus conferred greater drought tolerance. In addition, F. wislizeni could become established without benefit of nurse plants whereas C. gigantea could not; this might reflect differential tolerance to high soil temperatures.

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USGS1999

Aquifer-storage change in the lower Canada del Oro Subbasin, Pima County, Arizona, 1996-98

Aquifer storage was monitored using gravity methods in the Lower Canada del Oro subbasin from 1996 through 1998 to determine areas of infiltration and amounts of recharge along the Canada del Oro Wash after major surface flow and to estimate aquifer-storage change and specific-yield values for the regional aquifer. Both purposes were addressed by periodic monitoring of changes in aquifer storage and water levels at a network of gravity stations and monitor wells. Water levels and gravity were also monitored near an active withdrawal well for several months for the purpose of estimating specific yield of the aquifer within the cone of water-leel depression at the well.

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USGS1996

More flowers or new cladodes? Environmental correlates and biological consequences of sexual reproduction in a Sonoran Desert prickly pear cactus, Opuntia engelmannii

Should a platyopuntia expend all aerolar meristems in flower production, now new cladodes could be produced, and further reproductive effort and vegetative growth would cease. To investigate the trade-off between flower and cladode production, the numbers of flowers, fruits, and cladodes were monitored for 4 years on 30 Opuntia engelmannii Salm-Dyek, plants on Tumamoc Hill, Tucson, Arizona. Plant size controlled the number of flowers initiated each spring. The proportion of flowers that developed (i.e., did not abort) was perhaps determined by December-February rainfall in the months before bloom, with more being developed in the wettest years. Models based on different ratios of initiated cladodes to initiated flowers demonstrated that continued high investment in flowers and fruits would eventually terminate reproduction altogether; therefore periods of high sexual reproduction should alternate with periods of high vegetative growth. In the first 3 years of this study, the ratio of new cladodes to initiated flowers was low, showing a high investment in sexual reproduction. As suggested by the model, the population recouped this investment in the fourth year, when the number of new cladodes was nearly 3 times the 1992-1994 mean, and the number of initiated flowers was only 73% of the 3-year mean.

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USGS1996

Infiltration of wastewater effluent in the Santa Cruz River Channel, Pima County, Arizona

Infiltration of effluent into the Santa Cruz River channel from water-treatment plants near Tucson, Arizona was studied from March 23, 1990, to September 30, 1993. The study reach extended along a 23-mile stream reach from the water-treatment plants, about 5 miles northwest of central Tucson, downstream to Trico Road, about 5 miles west of Marana, Arizona. Data indicate that 88.4 to 90.2 percent of the effluent discharged from the two water-treatment plants infiltrated the Santa Cruz River channel. During 1991 93, the volume of effluent discharge that flowed out of the study area was 2,880, 4,120, and 3,320 acre-feet per year, respectively, and the volume of infiltration was 41,890, 43,640, and 45,670 acre-feet per year, respectively. Intermittent rainstorms resulted in high flows that altered the composition, structure, and geometry of the channel bed and may have caused the infiltration to increase to nearly 100 percent. In comparison, variations in evapotranspiration and open-channel evaporation had a minimal effect on the water budget. In the study reach, 3.2 to 3.9 percent of the effluent was lost to evapotranspiration and open-channel evaporation; 6.2 to 8.3 percent flowed through the reach.

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USGS1993

Channel change on the Santa Cruz River, Pima County, Arizona, 1936-86

The Santa Cruz River, an ephemeral river that drains 8,581 square miles in southeastern Arizona, has a long history of channel instability. Since the late 19th century, lateral channel erosion has caused extensive property damage, particularly in Pima County. During the flood of 1983, about $100 million damage was caused in the Tucson area alone; most damage resulted from bank erosion on the Santa Cruz River and its tributaries. The nature, magni- tude, location, and frequency of channel change on the Santa Cruz River were highly variable in time and space from 1936 through 1986 along a 70-mile reach in Pima County, Arizona. Four mechanisms of lateral channel change--channel migration, avulsion and meander cutoff, channel widening, and arroyo widening--were identified on the Santa Cruz River. The dominant mechanism in a reach depends on channel morphology and flood magnitude. The dominant vertical change has been degradation. The timing and magnitude of channel change at a particular location are controlled primarily by hydroclimatic factors such as magnitude, duration, intensity, and frequency of precipitation and floods. The location of channel change and its magnitude in response to a given discharge are controlled largely by topographic, geologic, hydraulic, and artificial factors. Although much of the present morphology of the Santa Cruz River is the result of recent large floods, a direct link between hydroclimatic con- ditions and channel change is not always evident because resistance of the channel to erosion varies with time. (USGS)

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USGS1982

Mineral resources potential map of the Pusch Ridge Wilderness Area, Pima County, Arizona

A mineral resource assessment of the Pusch Ridge Wilderness Area was conducted by the U.S. Geological Survey and U.S. Bureau of Mines. The area was evaluated for its mineral potential by analysis of geochemical samples by the U.S. Geological Survey and by examination of mines, prospects, and mineralized areas by the U.S. Bureau of Mines. The Pusch Ridge Wilderness Area has a low potential for minerals and little surficial indication of potential for oil, gas, or geothermal energy. Assignment of a low potential is based on consideration of geologic environments where mineral and other resources might be expected.

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USGS1982

Mine and prospect map of the Pusch Ridge Wilderness Area, Pima County, Arizona

The Endangered American Wilderness Act of 1978 created the Pusch Ridge Wilderness. During 1979, the U.S. Geological Survey and the U.S. Bureau of Mines investigated the area to evaluate the mineral resources. In addition to field investigations, studies by the Bureau of Mines personnel included courthouse research to ascertain claim locations within and near the area. Field work involved sampling and mapping located prospects. Rock samples were obtained from most of the working examined. A total of 55 samples were collected for assaying. All samples were fire-assayed for gold and silver, and at least one sample from each locale was checked by spectrographic analysis. Analytical results of all samples are available from the Bureau of Mines, Intermountain Field Operations Center, Denver Federal Center, Denver, Colorado 80225.

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USGS1978

Mineral resources of the Rincon wilderness study area, Pima County, Arizona

The Rincon wilderness study area comprises about 254 km 2 (98 mi 2 ) of the Rincon Mountains 15-30 km (10-20 mi) east of Tucson, Arizona. The area lies within the Coronado National Forest and forms a belt around the north, east, and south sides of the Saguaro National Monument (fig. 1). A mineral resource survey was made of the area in 1977 by the U.S. Geological Survey and the U.S. Bureau of Mines. This study indicates that the potential for finding metallic or nonmetallic mineral deposits, petroleum or coal or geothermal energy in the study area is low. This appraisal is based on geologic and geochemical investigations and on examination of all mineralized prospects. A geologic map was made of the area and its immediate surrounding. Chemical and spectrographic analyses were made of 1.30 stream-sediment samples and of 143 rock samples. The locations of mining claims were compiled and samples from most of the claims were assayed. There has been no recorded mineral production from within the study area. The geology of the Rincon Mountains is structurally complex. The core of the Rincon Mountains, lying mainly within the Saguaro National Monument, is underlain by igneous and metamorphic rocks chiefly of Precambrian and Tertiary ages. The study area lies on the flanks of the mountains in a terrain of sedimentary, metamorphic, and igneous rocks mainly of Precambrian through mid-Tertiary age. The rocks of this area are cut by many faults, with low-angle or bedding-parallel faults abundant. the distribution of these faulted rocks around the flanks of the Rincon Mountains is the result of a doming in the core area, the sliding of rock masses from the high part of the dome down its flanks, and to the effects of erosion. The potential for economic metallic mineral deposits is considered low because the known areas of anomalous concentrations of metals are small and the concentration of metals weak and erratic. The surface signs of mineralization are largely restricted to 4 locales in which some prospects exist (fig. 1): (1) east of Colossal Cave, southwest or the Rincon Mountains, (2) north of Happy Valley, east of the mountains, (3) between Roble and Youtcy Canyons, northeast of the mountains, and (4) near Italian Trap north of the mountains. Very little primary sulfide mineralization is present and signs of alteration are restricted to narrow zones along faults and fractures. The geochemical anomalies are weak. The sites at which anomalous values of copper, molybdenum, or silver were obtained are mainly controlled by faults. Nonmetallic mineral resources occur in deposits that are too small and too remote to be economically attractive. Sand and gravel deposits in the main drainages are similar to larger deposits that occur closer to nearby highways and cities. Limestone and marble present in some of the metamorphic rocks are too impure and too broken for use as dimension stone. Use of this marble as decorative rock is limited by remote markets. Limestone suitable for making cement is not likely to be found in large quantities within the Rincon wilderness study area. Closely spaced fractures in the granitic rocks makes them of little value for building stone.

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