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Trask Mountain in the Northern Oregon Coast Range, is the tallest mountain in Yamhill County, Oregon.〔 〕 It is located in the northwest corner of the county.〔 〕 Evidently the mountain was named for Elbridge Trask who settled west of the peak in Tillamook County in 1852. == 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 originated from fissures in the central portion of Oregon and covered much of the state.〔 (【引用サイトリンク】 Geologic Map of the Tillamook Highlands, Northwest Oregon Coast Range )〕 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Trask Mountain」の詳細全文を読む スポンサード リンク
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