Limited possibilities exist for new hydrocarbon exploration regimes in the Pacific Northwest. Extensive geophysical studies have been used to outline a proposed sedimentary basin hidden beneath volcanic rocks of the Cascades region of southwestern Washington (Stanley et. al, 1992, AAPG Bull. 76, 1569--1585). Electrical geophysical imaging using the magnetotelluric (MT) method first detected thick, electrically conductive sequences believed to represent late Cretaceous to Oligocene marine sedimentary rocks. The conductive section occurs at depths from about 1 km to 10 km in the area west of a line between Mt. Rainier and Mt. Adams, extending westward to a line between Mt. St. Helens and just west of Morton, WA. The conductive rocks reaches thicknesses as great as 10 km. The anomalous rocks appear to be very near the surface in the axis of anticanes that bring Eocene marine shales to shallow depths. Careful consideration of physical properties and the correspondence of the morphology of the units to known fold sets suggests that the high conductivities are related to lithologic/stratigraphic units rather than to variations in physical properties. Our preference for the lithology of the anomalous section, based upon a study of regional geology and structure, is one dominated by marine shales of Eocene and older age. Other possible lithologies that have been evaluated for the conductive section include nonmarine sedimentary units of Tertiary age, highly altered volcanic flows, and pre-Tertiary memsedimentary rocks with large percentages of graphite. We refer to this anomalously conductive region as the southern Washington Cascades conductor (SWCC).