The Pacific to Arizona Crustal Experiment (PACE) is a multidisciplinary transect which crosses an old magmatic arc, a continental rift, a transform plate boundary, and an extensional terrane located in southern California. This award supports a magnetotelluric survey along this transect. MT soundings, to date, have revealed a strong correlation with detachment fault geometry east of the Salton Trough in the Chocolate Mountains extensional terrane. Also, a regional detachment surface postulated by seismologists has probably been detected beneath the Peninsular Ranges.