A program of detailed magnetotelluric soundings was initiated in 1974 in Green Valley, Nevada, as part of the Lawrence Berkeley Laboratory's major study of techniques for geothermal exploration in north central Nevada. The magnetotelluric program had three main goals; the determination of resistivity distribution at depths greater than that conveniently measured with other techniques; a comparison of the interpreted resistivity at shallow depth with the results of the other techniques; and the evaluation of the SQUID or Josephson effect magnetometer in practical field surveys. In addition, new numerical models were developed so that interpretation could be carried out in terms of fairly complex two-dimensional models