Cascade volcanic-plutonic belt 

(late Eocene to Quaternary) 

(Central and southern Canadian Cordillera, and U.S.A. Pacific Northwest, units QTvi, QTvm, 
mTp)

In Canadian Cordillera, belt consists of Pleistocene-Holocene basalt, andesite, and dacite eruptive centers, 
and late Eocene(?), Oligocene, and Miocene plutons (Chilliwack and Mount Barr batholiths). Includes age-
equivalent, possibly unrelated volcanic rocks (Masset Formation) on the Queen Charlotte Islands.

In U.S.A. Pacific Northwest, the belt consists of volcanic rocks of stratovolcanoes, mostly andesite but 
ranging from basalt to rhyolite. Includes interbedded fluvial and lacustrine deposits and minor tonalite to 
granodiorite plutons. In Washington, parts of belt are included in the Ohanapecosh, the Fifes Peak, and the 
Northcraft Formations (Walsh and others, 1987; Vance and others, 1987; Smith, 1993). The Oregon parts 
of belt are included in many formations and informal units, listed in Walker and MacLeod (1991). 
Youngest active volcanoes include Mount Jefferson, Mount Hood, Mount Adams, Mount St. Helens, and 
Mount Rainier. The Cascade belt comprises the western part of unit QTvi in Washington and Oregon. East 
of the volcanoes, the belt includes units that are interpreted as backarc extensional volcanic rocks of 
Miocene to Holocene age, predominantly basaltic and rhyolitic volcanic rocks. REFERENCES: MacLeod 
and others, 1976; Green, 1981; Walsh and others, 1987; Vance and others, 1987; Wells, 1990; Walker and 
MacLeod, 1991; Smith, 1993