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Upper Mesa Falls : ウィキペディア英語版 | Upper Mesa Falls
Upper Mesa Falls is a waterfall on the Henrys Fork in the Caribou-Targhee National Forest. Upstream from Lower Mesa Falls, it is roughly away from Ashton, Idaho. Upper Mesa Falls is roughly high and wide. ==Formation==
Mesa Falls Tuff, which is the rock over which Upper Mesa Falls cascades, was formed 1.3 million years ago. A cycle of rhyolitic volcanism from the Henrys Fork caldera deposited a thick layer of rock and ash across the area.〔 〕 This layer compressed and hardened over time. Between 200,000 and 600,000 years ago, the river eroded a wide canyon which was subsequently partly filled with basalt lava flows. The Henrys Fork of the Snake River then carved the channel through the basalt; which is the inner canyon seen today.
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「Upper Mesa Falls」の詳細全文を読む
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