In June 1985, wide-band magnetotelluric data were acquired at twelve equally spaced sites along a 30~km profile crossing the Flathead (Kishenehn) Basin in southeastern British Columbia, Canada. These data have been modelled by both one-dimensional inverse techniques and two-dimensional forward trial-and-error fitting. The results indicate the presence of the following three major zones of low electrical resistivity (10 - 500 Ohm.m) in the area: 1: Sediments of the 10 km wide Flathead sedimentary basin, extending to a depth of about 2 km, dominate the responses in the middle of the profile. 2: In the eastern part of the profile, in the area of the Lewis Range, a thin zone of low resistivity ($\simeq$1~km, 35~\ohmm) is imaged at a depth of some 3 km extending eastward from the edge of the basin. We associate this zone with the less dense thrusted Mesozoic clastic rocks lying directly below the Proterozoic rocks of the Lewis Thrust Sheet. 3: Beneath the Flathead Basin is a third zone, of higher resistivity (500 Ohm.m), which extends to deep within the crust. This zone may originate from mantle upflow recently proposed to explain the existence of the Cordilleran conductors in other localities. Additionally, in order to model the long period geomagnetic transfer function responses, we are required to postulate the existence of a zone of low resistivity in the mid to lower crust 50 km west of the survey line, corresponding to the location of the Rocky Mountain Trench.