 To the east, across the Klickitat River, lies the Simcoe Mountains volcanic field. This area contains many small shield volcanoes and cinder cones of mainly alkalic intraplate basalt with fractionated intermediate alkalic products, subordinate subalkaline mafic lavas, and several rhyolites as secondary products. There are about 205 vents that were active between 4.2 million and 600 thousand years ago.
