Trask Mountain - Geology

Geology

The mountain is composed of mainly volcanic rock with some sedimentary rocks. Like much of the northern section of the Oregon Coast Range, the origins began around 40 million years ago during the Eocene period. During this era, sandstone and siltstone formed in the area. Additionally, igneous rocks and basalt flows combined with basaltic sandstone to create many of the mountainous formations. The volcanic rocks come from basalt flows that covered much of Oregon that originated from fissures in the central portion of the state. Additional sedimentary rock was formed more recently, around 20 million years ago.

All of the coast range lies over a convergent tectonic margin interacting with the Juan de Fuca Plate that is subducting beneath North America tectonic plate in the Cascadia subduction zone. The mountains are created by the plunging structural arch of sedimentary and Tertiary volcanic strata that is being uplifted.