Shallow soil conductivity was mapped in the San Luis Valley, Colorado, using the DualEM421 electromagnetic sensor in March 2020. Data were acquired by towing the DualEM421 sensor on a wheeled cart behind an all-terrain vehicle, with the sensor at a height of 0.457 m above the ground surface. Approximately 62 line-kilometers of data were acquired over an area of nearly 1.5 square kilometers, with 20 m separation between survey lines. Data were manually edited for noise sources (powerlines, pipelines, or other buried structures), and averaged to regular output soundings every 1 m along survey lines. Data were corrected for offset between the recorded GPS location and data locations for each coil pair, but were not...
Shallow subsurface electrical conductivity was mapped at selected U.S. Fish and Wildlife Service managed lands in northeast Montana and northwest North Dakota using the DUALEM421 electromagnetic sensor (Dualem, Inc., ON, Canada) in the winters of 2017 and 2018. Data were acquired by towing the DUALEM421 sensor on a sled behind an all-terrain vehicle or snow machine, with the sensor at a nominal height of 0.3 meters (m) above ground surface. Approximately 427 line-kilometers (km) of data were acquired over an area of nearly 26 square-kilometers. Data were manually edited to remove sensor dropouts, lag corrected for apparent offsets between recorded GPS location and data locations for each coil pair, and averaged...
Hydrologic reconnaissance of Mineral Creek near Silverton, Colo., was conducted from June 25-27, 2020. Both banks of Mineral Creek and the adjacent hillsides were walked, starting near the ghost town of Chattanooga and proceeding downstream to the confluence of Mineral Creek with the Middle Fork of Mineral Creek. The purpose of this reconnaissance was to identify areas of emergent groundwater on the right (EGR) and left (EGL) banks, a task that was accomplished by following observed surface flows (seeps and springs) upgradient to the point at which they emanated from the subsurface. Coordinates, using a handheld global positioning system (GPS) device, and photographs were obtained at these locations of emergent...
Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired September 2021 to January 2022 along 27,204 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP), Mississippi Embayment, and Gulf Coastal Plain. Data were acquired by Xcalibur Multiphysics (Canada), Ltd. with three different airborne sensors: the 30Hz TEMPEST time-domain AEM instrument that is used to map subsurface geologic structure at depths up to 300 meters (m) depending on the subsurface resistivity; a Scintrex CS-3 cesium vapor magnetometer that detects changes in deep (hundreds of meters to kilometers) geologic structure based on variations in the magnetic properties of different formations; and a Radiation Solutions...
Airborne electromagnetic (AEM) and magnetic survey data were collected during April and May 2019 along 1,467 line-kilometers in the San Juan-Silverton Caldera complex, Colorado, in the Southern Rocky Mountain Volcanic Field. Data were acquired by Geotech, Ltd. with the versatile time-domain electromagnetic (VTEM-ET) system together with a Geometrics optically pumped cesium vapor magnetometer. The survey was flown at a mean flight height of 140 meters (m) above terrain in various line directions and line spacings ranging from 150 m to 600 m. Multiple variable-spaced lines were flown along rivers and streams in the survey area. USGS provided the contractor with the San Juan National Forest Lidar Point Cloud elevation...