Geologic Map of Oregon
U.S. Geological Survey
Oregon is a mostly volcanic state, thanks to its position at the edge of the North American crustal plate where a small oceanic plate, the Juan de Fuca plate (and others before it), is being subducted beneath it from the west. This activity creates fresh magma which rises and erupts in the Cascade Range, represented by the stripe of medium-red in the western part of Oregon. To its west are more volcanics plus marine sediments from episodes when the crust was lower and the sea higher. Older rocks not quite covered by volcanic deposits are found in the Blue Hills of northeastern Oregon and in the northern Klamath Mountains in the extreme southwest, a continuation of the California Coast Ranges.
Eastern Oregon is divided between two large features. The southern part is in the Basin and Range province, where the continent has stretched in the east-west direction, breaking up into great blocks with intervening valleys, like the rocks of Nevada. The northern part is a vast expanse of lava, the Columbia River Basalt. These rocks were emplaced in fearsome fissure eruptions as the continent overrode the Yellowstone hotspot, during Miocene time some 15 million years ago. The hotspot has torched its way across southern Idaho and now sits at the corner of Wyoming and Montana beneath the geysers of Yellowstone National Park, far from dead.
This is a postcard-size version of U.S. Geological Survey Map I-595 by George Walker and Philip B. King, published in 1969. The 1200x1550 pixel version (1.1 MB) includes the explanation of the map units, and all of it is legible. The 2000x2600 pixel version (2.6 MB) is suitable for printing.
Back to Geologic Maps of the States
