Tensor apparent resistivity values obtained from the magnetotelluric field measurements, in the plains of Alberta indicate a major regional anisotropy. The direction of the major axis of the anisotropy is parallel to the strike of the Rocky Mountains and the sedimentary basin of Western Canada. Results obtained by numerical methods for a two-dimensional geoelectric model support an interpretation of the observed magnetotelluric results, depending on regional structures. The observed polarization parameters of the magnetotelluric fields are also in good agreement with those computed for the two-dimensional model. This study shows that the conclusions based on some earlier magnetotelluric results, which postulated an upper mantle conductivity layer must be treated with strong reservations.