Geomagnetic depth-sounding data have been obtained along a profile across the northern Yukon and the Mackenzie Delta region that approximately parallels the east–west flow of the auroral electrojets near the geomagnetic latitude of 70°N. An internal conductive zone, in which electric currents are confined to a north–south direction, is defined by the large spatial variation of the vertical component of the time-varying geomagnetic field and of the horizontal component parallel to the profile. This conductive zone, with a half width of about 50 km, correlates with the Blow Trough, an element of the Beaufort–Mackenzie Basin, that contains at least 5 km of Mesozoic and Cenozoic clastic sediments. Model studies suggest that up to 10 km of conducting sedimentary materials occur within a basin-shaped structure and that a conducting zone (20 km wide) extends this basin to a depth of 20 km in the Earth's crust. This deeper conducting zone could be the result of movements along the Rapid Fault array, which dissects the Blow Trough and which may have fractured the materials beneath the basin or displaced sedimentary masses to greater depths. The observed negative Bouguer gravity anomaly is consistent with such a structure.