piles and related intrusions ranging in composition from basalt to rhyolite and in age from about eight million years old in the west to about 3.5 million years old elsewhere. Major element analyses of Alert Bay volcanic and hypabyssal rocks suggest two different basalt-andesite-dacite-rhyolite suites with divergent fractionation trends. The first coincides with the typical calc-alkaline, Cascade trend, whereas the other is more alkaline and more Fe-enriched following a trend which straddles the calc-alkaline-tholeiite boundary. The western end of the Alert Bay Volcanic Belt is now about northeast of the Nootka Fault. However, at the time of its formation the volcanic belt may have been coincident with the subducted plate boundary. Also, the timing of volcanism corresponds to shifts of plate motion and changes in the locus of volcanism along the Pemberton and Garibaldi volcanic belts. This brief interval of plate motion adjustment at about 3.5 million years ago may have triggered the generation of basaltic magma along the descending plate edge. Because the Alert Bay Volcanic Belt has not been active for at least 3.5 million years, volcanism in the Alert Bay Volcanic Belt is probably extinct. The Chilcotin Group, a large igneous province and volcanic plateau in south-central British Columbia, consists of thin, flat-lying, poorly formed columnar basalt lava flows that have formed as a result of partial melting in a weak zone in the upper part of the Earth's mantle within a back-arc basin related to subduction of the Juan de Fuca Plate. Chilcotin Group volcanism occurred in three distant magmatic episodes, the first 16-14 million years ago, the seconed 10-6 million years ago and the third 3-1 million years ago. Anahim Peak, a volcanic plug near the eastern flank of the Rainbow Range, and other plugs penetrating the Chilcotin Group are suggested to be vents for basalt volcanism. These volcanic plugs form a northwest trend about inland from the Pemberton and Garibaldi volcanic belts and exist along the axis of the volcanic plateau. Silicic tuff lying between Chilcotin basalt lava flows, likely originated from explosive eruptions related to arc volcanism in the Garibaldi and Pemberton belts just to the west and was preserved between successive basaltic lava eruptions in the Chilcotin back-arc basin. It is suggested by geoscientists the Chilcotin Group forms a sequence of merged low-profile shield volcanoes erupted from central vents. British Columbia plume and rift complexes The Northern Cordilleran Volcanic Province of northwestern