General Geology

Rock types (illustrative photo)The Wallowa Mountains have been uplifted to almost 10,000 feet along a fault located on the northwestern edge of the mountains. This area consists of a few main formations of rocks. The rocks are as follows: Columbia River Basalts, Clover Creek greenstone, Martin Bridge Formation, Hurwal Formation, quartz diorite, granodiorite, and alluvial/glacial deposits. The Columbia River Basalts come from large fissure eruptions in the Lewiston area about 16 MA filling in the Columbia basin forming what is known today as the Columbia plateau. The quartz diorite and granodiorite formed from a pluton that is part of the Idaho batholith. The Clover Creek Formation consists of andesite, porphyritic andesite, and basaltic-andesite. These are from lava flows erupting from an old island arc identified as Wrangellia. Martin Bridge Formation is a very thick sequence of limestone and marble that was formed off the shores of Wrangellia. The Hurwal Formation consists of volcanics formed after the collision of Wrangellia. The collision of Wrangellia formed the batholithic complex that created the granitic rocks in the Wallowa region. The alluvial deposits found at the base of the Wallowa Mountains are from large glaciers that once occupied the Wallowa Mountains and have since receded creating large glacial moraines and leaving behind the glacial deposits we see today. All this information was taken from Notes on the Geology of Northeast Oregon written by Ellen Morris Bishop.

banded gneiss (photo)Banded Gneiss

metamorphosed to a gneiss with severe temperature and pressure

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andesites and breccia (photo)Andesites and Breccia

porphyritic andesite (top left), andesite (bottom), volcanic breccia (top right)

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limestones and marbles (photo)Limestone and Marble

from Martin Bridge Formation, marble (left), limestone (right)

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granitic rocks (photo)Granitic Rocks

granodiorite (left), quartz monzonite (right)

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deposits (photo)Deposits

Glacial till deposits created this large moraine.

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