As part of Lithoprobe's Southern Cordilleran transect investigations, magnetotelluric (MT) soundings were made at 160 sites providing unprecedented coverage from the Rockies to the west coast. Striking lateral variation, which spatially correlates with the morphogeological belt boundaries, is apparent at periods sensing the lower crust (~10 s). For the Rockies, MT phases are around 35 degrees, indicative of a moderately resistive (100's - 1000's Ohm.m) North American Basement. Foreland belt phases are transitional and increase from 60 degrees in the east to 70 degrees in the west. Omineca and Coast belt phases are high (75 degrees), implying a conductive (10-30 Ohm.m) lower crust, whereas Intermontane belt phases are more than 10 degrees lower (equivalent to ~150 Ohm.m). The regional variation in conductivity correlates to first order with surface heat flow changes along the profile and is also correlative with coincident seismic reflection sections in some aspects.