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We have observed several new features in recent controlled-source audio-frequency magnetotelluric (CSAMT) soundings on and around Mount St. Helens, Washington State, USA. We have identified the approximate location of a strong electrical conductor at the edges of and beneath the 2004–08 dome. We interpret this conductor to be hot brine at the hot-intrusive-cold-rock interface. This contact can be found within 50 meters of the receiver station on Spine 5, which extruded between April and July of 2005. We have also mapped separate regional and glacier-dome aquifers, which lie one atop the other, out to considerable distances from the volcano.

This paper is the fourth in a series on a play fairway analysis of geothermal resources across the State of Hawai‘i. Here we describe recent exploration activities that include groundwater sampling in ten locations statewide, as well as geophysical surveys on Lāna‘i, across the SW rift of Haleakalā Volcano (Maui), and surrounding Mauna Kea Volcano (Hawai‘i Island). We derive a first-order method for computing topographic stress using Green’s functions, finding that topography can induce appreciable crustal stress. We develop a new method for incorporating depth information about resistivity, density, and topographic stresses into our previously published equations to calculate resource probability and confidence. We incorporate newly collected and modeled data into our calculations to update statewide maps of probability and confidence. Lāna‘i Island and southeast Mauna Kea are identified as the top targets for exploratory drilling. The east rift of Haleakalā Volcano, the southern-most region of Mauna Loa’s SW rift (Hawai‘i Island), and central Kauai are identified as targets for geophysical surveying.

Audio-magnetotelluric soundings collected near and within the Edwards Aquifer recharge area along Seco Creek in Medina County, Texas show the electrical structure of the Glen Rose and Edwards Group rocks within the uppermost 800 meters. These soundings were collected to test the efficacy of the technique, provide ground truth for an airborne survey, and map hydrogeologic features along Seco Creek where most of the surface water runoff is captured by the Edwards aquifer. Electrical sections generated from the data suggest several three-dimensional geologic structures. These structures are part of one of the nations largest limestone groundwater aquifers that discharges almost 1 million m3 per day providing water to millions of people in the San Antonio/Austin region. The data indicate northeasttrending gradients consistent with the mapped geologic structures associated with the Balcones fault system.

The Farlin Creek Wilderness Study Area (MT-076-034) is in the south-central Pioneer Mountains about 24 miles west-northwest of Dillon, Beaverhead County, southwestern Montana. At the request of the U.S. Bureau of Land Management, an area of 610 acres (less than 1 square mile) was investigated by the U.S. Geological Survey and the U.S. Bureau of Mines in 1984. The area contains no mines or prospects, no visible evidence of mineralization, and no identified mineral resources. Geophysical evidence suggests that three parts of the area have moderate mineral resource potential for undiscovered resources of molybdenum. The entire area has a low resource potential for all other metals and for all nonmetals, fuels, and geothermal energy.

A U.S. Geological Survey report is presented giving an Electrical survey of the Honey Lake valley, Lassen County, California and Washoe County, Nevada.