As part of EMSLAB, broadband magnetotelluric data have been collected and analyzed at 11 sites along an east-west transect in the Oregon Coast Range. Using one- and two-dimensional modelling, the Coast Range was found to consist of marine sediments about 4 km deep near the coast and volcanic rocks about 8 km deep farther inland. Willamette Valley consists of surficial conductive sediments to a depth of 1 km, which overlie an eastern extension of the rocks that compose the Coast Range. An east diping conductor, at a depth of approximately 20 km, is associated with the upper surface of the subducting Juan de Fuca plate. Possible mechanisms for the high conductance are water-saturated fractured basalts forming the surface of the plate, subducted sediments, and/or the dehydration of the subducting slab trapped by metamorphic layering within the lower crust. This conductor correlates with an east dipping reflector, 35--40 km below the eastern flank of the Coast Range, defined by COCORP profiling and thought to represent the surface of the subducting Juan de Fuca plate. ¿ American Geophysical Union 1989