 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.