Geology
Many geologists believe the Wallowa Mountains in northeastern Oregon are a displaced fragment of the Insular Belt. The Wallowa Batholith is formed of granite from a magma upwelling in Late Jurassic and Early Cretaceous time (between 160 million and 120 million years ago). The placement of this rock caused uplift of the surface, which at the time was tropical sea. This is evident from the slate, quartzite, and marble present in the mountains, which come from metamorphism of the sedimentary deposits of oceans during the Triassic. At the center of the Batholith are granodioritic rocks, while the outer limits of the range are tonalitic. The granite batholith is cut by dikes; however, these are uncommon.
Glaciers carved out the valleys during the late Pleistocene, which left a number of moraines. The series of moraines is formed by a series of glacial advances and retreats. Glacial till is also a common feature of the valleys. The melting of the glaciers produced a large quantity of water, which carried sediment to the valley bottoms, leaving delta deposits on top of the former deposits.
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