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 Santa Clara River Lakes, located along the San Andreas fault 19 miles northwest of Palmdale, California, were placed on the state’s “303(d) List” or “Impaired Water List” in 1996 for eutrophic conditions, high pH, and low dissolved oxygen. In 2016, the state adopted a Total Maximum Daily Load (TMDL) for nutrients (nitrogen and phosphorus) in the Santa Clara River Lakes. This study focuses on the largest of the three lakes, Lake Elizabeth, which is surrounded by the unincorporated town of Elizabeth Lake, CA. The local community uses on-site wastewater treatment systems instead of a centralized sewer system, resulting in potential contamination of groundwater. In response to concerns over the quality of water in the area and fluctuating water levels in Elizabeth Lake, the U.S. Geological Survey (USGS) cooperated with the Los Angeles Regional Water Quality Control Board to assess hydrologic conditions and water quality near Elizabeth Lake. As part of this work, the USGS did electrical resistivity tomography (ERT) survey lines at two locations across the southern edge of the lake near the community in March 2019.

Hi-Desert Water District (HDWD) is constructing a wastewater treatment plant as part of a groundwater replenishment and reuse project (GRRP) in the east hydrogeologic unit (Nishikawa, and others, 2003) of the Warren Valley Basin (7-012) (California Department of Water Resources, 2016) in Yucca Valley, CA. The HDWD plans to use reclaimed wastewater for managed aquifer recharge by spreading treated wastewater into unlined ponds at the GRRP facility. Reclaimed wastewater will percolate through the unsaturated alluvium by gravity drainage through the unsaturated zone to the water table located about 370 feet (ft) below land surface (bls). As part of the cooperative efforts between the HDWD and the USGS, the electrical resistivity tomography (ERT) geophysical surveying technique was proposed to monitor the movement of reclaimed wastewater through the unsaturated zone to the water table. This data release presents ERT data collected before water was placed into the ponds. Data from two ERT surveys (YVHDWW_L1 and YVHDWW_L2) were collected in May and September of 2019 to determine background resistivity values for the unsaturated alluvium south of the GRRP facility prior to recharge. The surveys were collected normal to each other and located downslope from the GRRP facility. This location was chosen in order to collect resistivity data in anticipation of movement of recharged water downslope through the unsaturated zone.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 mi north-northeast of Barstow, California, covers approximately 1,177 square miles, and is comprised of ten groundwater basins, three of which have been subdivided into subbasins on the basis of additional hydrologic testing. Since the early 1990s, the U.S. Geological Survey (USGS) has been studying water resources issues at Fort Irwin. One issue of concern is the potential effect of groundwater development resulting from planned training expansion and infrastructure at the NTC on natural springs and seeps, an important water source for wildlife. In 2010, the USGS entered into cooperative agreements with the U.S. Army to complete studies of groundwater resources focusing primarily on undeveloped basins within the NTC. Electrical resistivity data were collected in 2015 and 2017 at three groups of springs in undeveloped basins in order to quantify the spatial extent of groundwater associated with each spring and to detect hydrologic change over this two year time period. In 2017, electrical resistivity data were also collected at the airstrip on Bicycle Lake (a dry lakebed) to provide insight on ground failures and data regarding the depth of the known surface cracks and macropolygon features.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 mi north-northeast of Barstow, California, covers approximately 1,177 square miles, and is comprised of ten groundwater basins, three of which have been subdivided into subbasins on the basis of additional hydrologic testing. Since the early 1990s, the U.S. Geological Survey (USGS) has been studying water resources issues at Fort Irwin. One issue of concern is the potential effect of groundwater development resulting from planned training expansion and infrastructure at the NTC on natural springs and seeps, an important water source for wildlife. In 2010, the USGS entered into cooperative agreements with the U.S. Army to complete studies of groundwater resources focusing primarily on undeveloped basins within the NTC. Electrical resistivity data were collected in 2015 and 2017 at three groups of springs in undeveloped basins in order to quantify the spatial extent of groundwater associated with each spring and to detect hydrologic change over this two year time period. In 2017, electrical resistivity data were also collected at the airstrip on Bicycle Lake (a dry lakebed) to provide insight on ground failures and data regarding the depth of the known surface cracks and macropolygon features.