The Little Colorado River alluvial aquifer near Leupp, Arizona was investigated as a possible source of irrigation water for the Leupp and Birdsprings Chapters of the Navajo Nation. The physical, chemical, and hydraulic characteristics of the alluvial aquifer were studied using geophysical surveys, installation of observation wells, water-level measurements, chemical analyses, groundwater pumping simulations, and review of previous investigations. Geophysical surveys and well borings were used to measure the thickness of the aquifer. Geophysical surveys included Electrical Resistivity Tomography (ERT) to better define the alluvial channel of the Little Colorado River near Leupp. ERT is a commonly used electrical geophysical technique for investigating the subsurface of the Earth. In this study it was tested in two separate areas to determine how effective the technique would be for determining the thickness of the alluvial sediments along the LCR. An Advanced Geosciences Inc. Supersting R8TM multi-channel resistivity/IP meter with a SwitchBox56® was used for the DC resistivity survey and all DC resistivity survey data was modeled using Advanced Geosciences Inc. Earthimager 2D software. For each survey line, 56 electrodes were placed on the ground with a spacing of 5 meters (except Line MB4 had a spacing of 6 meters) for the initial survey segment and when the segment was completed then the first 28 electrodes of the survey were moved to the end of the survey line in a roll-along technique. The survey line can be extended indefinitely in a leap-frog fashion even though each segment is only 56 electrodes at a fixed spacing of 5 meters. Resistivity measurements were made in different arrangements or arrays of electrodes, and for this survey dipole-dipole and strong-gradient arrays were used. For both array types, an electrical current is transmitted into the ground, and the resulting potential differences are measured at the surface (Sharma, 1997). Layers within the Earth that are electrically conductive or resistive will deflect or distort the normal potentials.

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).

The Cahuilla Valley and Terwilliger Valley groundwater basins, 9-006 and 7-026 respectively (California Department of Water Resources 2016) located approximately 25 miles southwest of Palm Springs, are the sole-source for groundwater supply for the rural disadvantaged community and two Native American Tribes, the Ramona Band of Cahuilla and the Cahuilla. The characteristics and sustainable yield of the Cahuilla Valley and Terwilliger Valley groundwater basins are not well understood and are threatened by increasing water use and potential changes in water sustainability related to climate change. Previous USGS studies of the Cahuilla-Terwilliger Valley groundwater basins defined the thicknesses and characteristics of the alluvial sediments that constitute the main water-bearing unit of the aquifer system and identified where wells completed in the underlying fractured bedrock are located (Moyle, 1976; Landon and others, 2015; Woolfenden and Bright, 1988). However, although the fractured bedrock is an important part of the aquifer system for domestic and some irrigation supply, the thickness and hydraulic characteristics of the fractured bedrock are not well understood (Landon and others, 2015; Moyle 1976). Existing gravity data identified a possible conduit for groundwater flow beneath Cahuilla Creek in the Cahuilla and Durasno Valleys (Landon and others, 2015). Electrical resistivity tomography (ERT) data was collected in August 2018 to evaluate the cross-sectional depth to bedrock underlying a narrow section of Durasno Valley, and to help select locations for groundwater monitoring wells. Data from two transects were collected perpendicular to Cahuilla Creek, and offset by approximately 600 meters (m).