An audiomagnetotelluric (AMT) sounding system developed by the U. S. Geological Survey appears to be an effective technique for reconnaissance exploration to detect shallow resistivity anomalies associated with geothermal reservoirs. The equipment operates within the frequency range of 8--18,600 Hz by using nine logarithmically spaced narrow band filters. The technique has been evaluated in Long Valley, California, where the results from dc resistivity and time domain electromagnetic surveys were available for control. The AMT method outlines two linear zones of low resistivity that correlate well with known hot springs in the area. Generally, good agreement was obtained with the results of other electrical methods.