Geologic Formations

Mount Rainier, rising to 14,410 feet and surrounded by a dramatic landscape of volcanic ridges and glacier-carved valleys, is an icon on the horizon in the Pacific Northwest. Look closer, and this familiar landscape contains the origin story of this area. It has been covered in swamps and ancient seas, flowing lava, explosive ash, and thick sheets of ice. Mountains rose and eroded away. The features described on this webpage provide an outline of Mount Rainier’s geologic past, but it does not cover every formation you may observe while exploring the park.

For a detailed geologic history of Mount Rainier, visit:
Geology of Mount Rainier - U.S. Geologic Survey
Roadside Geology of Mount Rainier National Park and Vicinity – Patrick T. Pringle, Washington Division of Geology and Earth Resources, Information Circular 107, June 2008.

 

Geologic Formations of Mount Rainier

This map highlights some of the geologic formations found in Mount Rainier National Park found in different time periods. For the best viewing experience, click on "View full screen" in the lower left corner. 
 

Pre-Mount Rainier Geology

Formed over the last 500,000 years, modern Mount Rainier is a relatively young volcano standing on a foundation of rocks millions of years old. Some of these pre-Mount Rainier formations include:

 
An exposed rock face surrounded by bushes and vegetation along a muddy dirt road. The rock face has vertical layers angled to the left with faint ripple marks.
Puget Group rock formation along Mowich Lake Road (SR165), just outside the border of the park.

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Puget Group, 40+ million years ago
Over 40 million years ago, lowland swamps left behind layers of sandstone, shale, and coal. This coal was later mined near the Carbon River area, outside the northwest corner of the park.

 
Thick bands of darker grey and crumbly tan-orange rock layered diagonally in a cliff face traversed by a paved road.
Ohanapecosh Formation (darker grey rocks) along SR410.

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Ohanapecosh Formation, 26-28 million years ago
Ancient Ohanapecosh Formation volcanoes erupted underwater, forming layers sandstone and breccia that have been compressed and folded over millions of years. These layers are visible between Cayuse Pass and Tipsoo Lake along State Route 410.

 
White and tan cliffs hang over a paved road.
Stevens Ridge Formation cliffs along Stevens Canyon Road.

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Stevens Ridge Formation, 26 million years ago
Early volcanoes erupted pumice and welded tuff. Visible in cliffs west of Box Canyon along Stevens Canyon Road.

 
Dark grey rocks, streaked lighter grey in sections, next to a paved road.
Tatoosh Granodiorite rocks along the White River Road.

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Tatoosh Granodiorite, 18-14 million years ago
A large mass of molten rock slowly cooled under the surface, forming granodiorite, a rock similar to granite. This granodiorite underlies the Tatoosh Range, White River, Carbon River, and Nisqually River Valleys. View it up-close along White River Road near the White River Campground.

 
A series of mountain ridges with two distant volcanic peaks rising above them.
Mount Adams, and distant Mount Hood, rise above the mountain peaks and ridges of the Cascade Range, as viewed looking south from Panhandle Gap on the east side of Mount Rainier.

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The Cascade Range
The Cascade Range starts to rise through subduction uplifting 10 million years ago, completing the geologic foundation of the Mount Rainier.

 

Formation of Mount Rainier

A subduction zone is an area where one tectonic plate is being forced underneath another into the earth's mantle. Approximately 50 miles down, chemical changes lower the melting point of rock, causing the subducting slab to partially melt, creating magma. Some magma bubbles to the surface of the earth and erupts out of volcanoes as lava. An ancestral volcano stood in the same place as modern Mount Rainier from 1-2 million years ago. It largely eroded during a period of low volcanic activity before modern Mount Rainier started to rebuild.

Modern Mount Rainier was built by numerous eruptions over the last 500,000 years, alternating between periods of high volume and low volume eruptions. These eruptions built up layer after layer of lava and loose rubble, eventually forming the tall cone that characterizes composite volcanoes. Some of these eruptions produced notable features on Mount Rainier that are still visible today.

 
A rounded ridge of grey rock in front of the glaciated peak of Mount Rainier.
Burroughs Mountain, the rocky, rounded formation in front of Mount Rainier, as viewed along the Sourdough Ridge Trail at Sunrise.

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Burroughs Mountain, 500-420 thousand years ago
Built during a very active eruptive period and some of the oldest lava flows in the park. Visible from the Sunrise Area.

 
Steep grey cliffs along a forested ridge.
Rampart Ridge viewed from the Longmire Area.

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Rampart Ridge, 380 thousand years ago
Began as a lava flow that formed against a wall of glacier ice, creating the steep lava cliffs visible from Longmire today.

 
A sharp, triangular peak of crumbly dark rock along a ridge above a glacier.
Little Tahoma viewed from the Sunrise Area.

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Little Tahoma Peak, 160-40 thousand years ago
Formed from dikes and vents feeding lava to the side of Mount Rainier, instead of erupting from the summit. This prominent feature on Mount Rainier's eastern slopes can be viewed from many locations in the park.

 
A large, flat-topped rock feature on a ridge above a glacier.
Gibralter Rock, a distinctive flat-topped rock feature on the upper mountain, as viewed from the Nisqually Vista Trail at Paradise.

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Gibraltar Rock, 40-14 thousand years ago
Rocks of many ages are exposed in the upper mountain features of Liberty Ridge, Willis Wall, Success Cleaver, and Gibraltar Rock.

 
Thin rock ridges descending down the middle of a glacier.
Lava ridges breaking through the Emmons Glacier, viewed from the Emmons Vista Overlooks at Sunrise.

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Emmons Glacier Lava Flows, 2.2 thousand years ago
Mount Rainier’s youngest features are the summit craters built around 1,000 years ago, and small surface lava flows under the Emmons and Winthrop Glaciers. Edges of these lava flows are visible breaking through the Emmons Glacier.

 
Layers of different ash and debris attached to a board, with one layer marked by a label "4".
A portion of an exhibit at the Sunrise Visitor Center showing different layers of ash found at Mount Rainier. Layer 4 is ash from the Summerland Series, a combination of six ash and tephra layers from Mount Rainier eruptions 2,200-2,700 years ago.

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Volcanic Ash
Mount Rainier has erupted numerous times. Ash, both from Mount Rainier and neighboring volcanoes like Mount St. Helens, created layers interspersed by rocks from debris flows and glaciers. These strata layers visible throughout the park and are a detailed timeline of Mount Rainier’s relatively recent past.
 
A cliff of roughly octagonal columns of grey rock.

Volcanic Features

Mount Rainier is a volcano and many volcanic features can be found in the park.

A glacier carves down a mountain slope into a forested river valley.

Sunrise Geology

The road from White River to Sunrise is a journey through the geologic history of Mount Rainier. Discover geology through this audio tour.

A climber stands on the edge of a large glacier crevasse.

Glacier Features

Learn about the unique features and formations created by glaciers and glacial forces.

Last updated: February 14, 2022

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