Okanogan Highlands | Northern Cascades | Southern Cascades | Olympic Mountains |
Willapa Hills | Columbia Basin | Blue Mountains | Puget Lowland | Portland Basin
Washington is uniquely positioned for the study of the geologic and structural setting of western North America. To the southeast, in Oregon and Nevada, extensional features predominate as reflected by basin-and-range terrain. To the east, the Rocky Mountains influence the geology of Idaho. To the north, western British Columbia is characterized by a massive coastal crystalline belt and remnants of the geologic continent Wrangellia. All of these major crustal features of the adjacent regions terminate in Washington.
The state's uniqueness is further enhanced by two major geologic conditions. First, Washington is impacted by crustal tectonics as the oceanic Juan de Fuca plate is being forced under the North American continent through a process called subduction. Second, the Columbia Basin in Washington and adjacent Oregon was subjected to one of the greatest outpourings of basalt known in the geologic record.
Washington's geology is highly diverse. Rocks of Precambrian age, as well as units from every geologic period, Cambrian to Quaternary, are represented. The area of the state has been subject to continental collisions, metamorphism, intrusion of igneous rocks, volcanism, mountain-building episodes, erosion, and massive flooding events. This diversity has a strong influence on soil productivity, location of mineral deposits, scenic grandeur, and even the climate.
The easiest way to understand Washington's complex geology is to examine each physiographic region individually.
Okanogan Highlands | Northern Cascades | Southern Cascades | Olympic Mountains |
Willapa Hills | Columbia Basin | Blue Mountains | Puget Lowland | Portland Basin
References
The above text is modified from the following article: Lasmanis, Raymond, 1991, The geology of Washington: Rocks and Minerals, v. 66, no. 4, p. 262-277. © Copyright Heldref Publications (Helen Dwight Reid Educational Foundation). Used with permission.