Reconnaissance geophysics of a known geothermal

Audio-magnetolelluric (AMT) and telluric current soundings were made in a study ofthe geothermal poten-tial of the area between Weiser, Idaho and Vale, Oregon, during the spring and fall of 1974. The electrical surveys covered an area on the westem edge ofthe Snake River plain of approximately 3500 km * with 89 AMT and 31 telluric current stations at approximately 6-km spacings. The AMT method used the natural electromagnetic (EM) field from 7.5 Hz to 6.7 kHz (10 frequencies) with two VLF radio sources at 10.2 and 18.6 kHz, while the telluric method utilized geomagnetic micropul-sations, band-limited from 0.02 to 0.1 Hz. Maps were compiled using both methods to outline major high-and low-resistivity features. Major high-resistivity zones appear to trend northwest on the AMT apparent resistivity maps. These zones parallel structural trends between Vale and Weiser. The lowest apparent resistivities are associated with the known geothermal hot springs in the Vale and Weiser areas. The telluric ratio map shows lowest values at the eastem side ofthe area, and a low trend extending through Vale and to the northeast