Five magnetotelluric stations were operated in two clusters in southern British Columbia and Alberta, in order to determine the conductivity structures in each of the two main regions delineated by geomagnetic depth-sounding. A wide period range was covered (20 to 7500 seconds), to permit resolution of structure at lower crustal and upper mantle depths.At the eastern cluster (Pincher, Fernie), a moderately conducting zone (30–50 ohm-meters) is defined starting at depth 30–35 km and extending to a depth of at least 100 km. At the western cluster (Penticton, Osoyoos, Grand Forks) a conducting layer (10 ± 5 ohm-meters) starts at depth 15 ± 5 km; below this layer (of thickness 20–40 km) the resistivity increases to a value of the same order (30–50 ohm-meters) as at the eastern cluster.

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