Geologic map of the Vanson Peak Quadrangle, Lewis, Cowlitz, and Skamania counties, Washington.

Abstract

The Vanson Peak Quadrangle, located about 25 km north of Mount St. Helens, is underlain by Oligocene volcanic and volcaniclastic rocks locally veneered by Pleistocene glacial deposits. The Tertiary rocks are dominantly basalt and andesite flows and associated fragmental rocks deposited in a subaerial environment. They have been gently tilted to the east and intruded by granitic rocks of the 21-Ma Spirit Lake Pluton. Extrusive and intrusive rocks are locally hydrothermally altered to clay-carbonate and advanced argillic assemblages. Late Pleistocene till mantles much of the center of the quadrangle and thick outwash deposits are present in the Cowlitz River valley in the northern part of the quadrangle.

40 samples from this reference