Editing Chilcotin Group (section)

==Formation of the Chilcotin Plateau Basalts==
[[Image:Chasm Provincial Park trees and flood basalts.jpg|thumb|left|Cliffs made of low viscosity lava flows in Chasm Provincial Park suggest extensive volcanic activity in the Chilcotin Plateau Basalts]]
The distribution and volume of the Chilcotin Group is unknown due to extensive Pleistocene glacial cover. This presumably glacial "drift" is very thick, and in most regions completely obscures the volcanism. Individual vents for [[basalt]] volcanism include small [[cinder cone]]s, [[volcanic plug]]s, and [[gabbro]]ic feeders, which locally crosscut lava flows. Recent studies indicate that the volume of the Chilcotin Group is much less than previously thought, and that the "Plateau" is likely Eocene in age. This means that the Chilcotin is likely composed of many local volcanic vents, that were of small volumes that fed into the paleo-landscape, and subsequently are found in the major river systems that we see at present.

Prior to 16 million years ago, the western [[Cascade Volcanoes|Cascade Volcanic Arc]] [[stratovolcanoes]] erupted with periodic regularity for over 27 million years, even as they do today. The ultimate cause of this volcanism is still up for debate, however, the most widely accepted idea is that a [[back-arc basin]] behind the [[Cascadia subduction zone]] initiated the widespread and voluminous basaltic volcanism.<ref name="SI"/> Some centers erupted along pre-existing brittle [[fault (geology)|fault]] systems while volcanism along its northern portion is most widely believed to have been related to a centre of upwelling [[magma]] called the [[Anahim hotspot]] (similar to that associated with present-day Hawaii), creating the [[Rainbow Range (Coast Mountains)|Rainbow]], [[Ilgachuz Range|Ilgachuz]] and [[Itcha Range]] [[shield volcano]]es which also in turn form part of the [[Anahim Volcanic Belt]]. The exact nature of the relationship between the Anahim hotspot and the Chilcotin Group is unknown, however.