 During a period of 3 million years , extrusion of undersaturated trachyte flows built up the gently sloping Late Pliocene @-@ to @-@ Pleistocene Itcha Range . It is the easternmost and youngest of the three large felsic shield volcanoes lying on an east @-@ west trend in west @-@ central British Columbia . It has a diameter of 15 km ( 9 mi ) . The broad scale morphology of the Itcha shield is given by the extensive lateral distribution of thick ( 70 – 150 m ( 230 – 490 ft ) ) felsic flows which erupted from fissure vents around a central vent to cover an area of 330 km3 ( 79 cu mi ) . Most late @-@ stage lavas capping the Itcha shield complex were erupted from cinder cones , tuff rings , and fissure vents in the eastern half of the complex about 80 @,@ 000 years ago . 
