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Geology of the National Parks


View to south from Mount Claywood
View south from Mount Claywood

The Unique Mountains

Along the west coast of North America, from Mexico to southern Canada, are mountain ranges of diverse character collectively called the Coast Ranges (fig. 1). The Olympic Mountains, at the extreme north-west corner of the conterminous United States, are a unique part of these ranges. Even though they are closely related in rock composition to the Coast Ranges of Oregon, they are separated from them by the broad lowland of the Chehalis River and are considerably higher and more rugged. They have some scenery in common with the Insular Ranges of Vancouver Island in Canada but are quite different geologicalIy.

Location of the North Cascades.
Fig. 1. Mountain ranges along the Pacific Coast

Viewed from above, the Olympics seem to present a disorganized, circular array of jagged peaks above a deep, forested labyrinth of canyons; but the dominant design is controlled by eleven major rivers radiating from the mountains like the spokes of a wheel. This circular spread and radial river plan show that the Olympics developed as a separate uplift, not as a part of a long, coastal mountain chain. They comprise a mountain massif in themselves. Between the major rivers in the core of the range are extensive tracts of alpine and subalpine terrain: flowered meadows, barren rocky expanses, and glacial ice.

The major rivers the Skokomish, Hamma Hamma, Duckabush, Dosewallips, Dungeness, Elwha, Soleduck, Bogachiel, Hoh, Queets, Quinault, Humptulips, and Wynoochee carry a tremendous volume of water because the high Olympics, intercepting Pacific storms, receive more rain and snow than any other place in the conterminous states. In the coastal area, precipitation averages about 140 inches per year and in the high mountains it may approach 200 inches; but on the northeast side of the peninsula, in the lee of the mountains, rainfall decreases rapidly to less than 20 inches in the Sequim area. Most rain and snow falls in the winter months, but the rivers are fed around the year by melting winter snow and glaciers.

Early Exploration: The Geographic Map

The Olympics lay obscure and remote long after the rest of the western United States was well explored and mapped. Although there was some settlement around the periphery of the Olympic Peninsula, maps of the mountain region made as late as 1890 were blank in the center.

Official exploration of the mountains got under way in 1885 when a party led by Lieutenant Joseph O'Neil of the U.S. Army reached the high country of the Hurricane Ridge area and explored to the south. O'Neil returned in the summer of 1890 to construct a mule trail up the North Fork of the Skokomish and down the Quinault. While accomplishing this remarkable task, he and his exploring parties also traveled the South Fork of the Skokomish, the Humptulips, the Wishkah, the Satsop, the Wynoochee, the North Fork of the Quinault, the Upper Elwha, and the Queets!

Lieutenant O'Neil's monumental but little-publicized exploration was outshone by the efforts of another party, the Press Exploring Expedition, sponsored, and well publicized, by a Seattle newspaper. The Press party, launched with great journalistic fanfare, barely made it across the mysterious range via the Elwha and Quinault rivers. Robert L. Wood tells the almost comical story of this expedition in his delightful book, Across the Olympic Mountains: The Press Expedition, 1889 - 90.

After these explorations, peaks and rivers finally began to be recorded on maps. Wood has neatly summed up the story of Olympic exploration and the evolution of Olympic National Park in another book, Trail Country: Olympic National Park.

Despite increasing travel and geographic exploration in the back country, little has been known about the geology of the mountains until recent times. The geology has remained obscure largely because of the mountains' steepness, heavy vegetation, and inaccessibility. Olympic rocks are also difficult to understand, and only recently have geologists had the concepts and tools to work with such rocks.

On to How the Geologist Explores: The Geologic Map

Material in this site has been adapted from Guide to the Geology of Olympic National Park by Rowland W. Tabor, of the USGS. It is published by The Northwest Interpretive Association, Seattle.

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