The
Paleocene to
Eocene volcanics consist of
volcanism flows and
sills of
tholeitic to
alkalic basalts with associated
tuff breccia,
siltstone and
sandstone. The flows are
vesiculated with
zeolite filled amygdules. The volcanics originated as
oceanic crust and
seamounts.
Potassium argon dating gives ages of 58.1 ± 1.5 to 50.7 ± 3.1 Ma;
Selandian to
Ypresian. The volcanics occur in the following counties of western
Oregon:
Benton,
Coos,
Douglas,
Lane,
Lincoln,
Polk,
Tillamook,
Washington and
Yamhill. == See also ==