Geology of Olympic National Park, Washington

Geodiversity is the full range of a park's geologic resources — rocks, minerals, sediments, fossils, landforms and the processes that shape them — together with its soils. The National Park Service's Geodiversity Atlas, produced by the Geologic Resources Inventory, collects that information for education, geoconservation and the joint management of each park's living and non-living resources.

Wildflowers below the Olympic Mountains. Image from the National Park Service's page.

The park

• Olympic National Park lies on the Pacific coast about 72 km (45 miles) west of Seattle, in Clallam, Grays Harbor, Jefferson and Mason counties, northwestern Washington.
• First authorized as Mount Olympus National Monument on March 2, 1909, it was renamed and redesignated a national park on June 29, 1938.
• It covers about 373,383 hectares (922,650 acres): glacier-capped mountains, deep valleys, meadows, lakes, old-growth forest, temperate rain forest and more than 113 km (70 miles) of Pacific beach.
• It is home to more than 1,000 plant species, hundreds of bird species and 70 mammal species, including the native Olympic marmot and herds of Roosevelt elk.
• Hundreds of archeological sites record more than 12,000 years of human presence, and historic sites trace 200 years of exploration, homesteading and community-building.
• It was named an International Biosphere Reserve in 1976 and a World Heritage Site in 1981.

How the mountains formed

Olympic's rocks are mostly igneous and sedimentary, formed in the last 60 million years, since the Paleocene.

1. Many of the formations that now make up the high peaks were laid down offshore as an accretionary prism.
2. As the dense Juan de Fuca Plate dives beneath the North American Plate, sediment riding on it is scraped off and pressed against the continent's edge. This convergence has been adding foreign rock to western North America since the Eocene (about 34 million years ago).
3. Millions of years of continuous subduction have folded, thrust and uplifted these rocks into Olympic's mountains — and they are still rising.

Hurricane Ridge is a good example: ancient sea-floor rock now standing about 1,830 m (6,000 feet) above sea level.

Features to look for

• Sea stacks — jagged rocks along the coast, made of the Hoh rock assemblage;
• coastal cliffs;
• glacially carved lakes, such as Lake Crescent;
• glacial landforms: U-shaped valleys, erratics and scree fields.

Sea stacks along Olympic's coast. Image from the National Park Service's page.

Olympic belongs to the Pacific Border province and shares its geologic history with a region far beyond the park.

Maps and reports

The Geologic Resources Inventory produces digital geologic maps and reports for more than 270 natural resource parks — scoping summaries, GIS maps, reports, posters and project overviews, available through the NPS DataStore. A Soil Resources Inventory for Olympic has been started.

Sources

Based on "NPS Geodiversity Atlas—Olympic National Park, Washington," National Park Service; a work of the United States government in the public domain.