Geologic Formations of Mount Rainier
Explore Mount Rainier's geologic history through this selection of geologic formations.
Puget Group, 40+ million years ago
Puget Group, 40+ million years ago. Click to expand.
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. This rock outcrop is visible along Mowich Lake Road (SR165), just outside the border of the park.
Ohanapecosh Formation, 36-28 million years ago
Ohanapecosh Formation, 36-28 million years ago. Click to expand.
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.
Stevens Ridge Formation, 26 million years ago
Stevens Ridge Formation, 26 million years ago. Click to expand.
Early volcanoes erupted pumice and welded tuff. Visible in cliffs west of Box Canyon along Stevens Canyon Road.
Tatoosh Granodiorite, 18-14 million years ago
Tatoosh Granodiorite, 18-14 million years ago. Click to expand.
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.
Burroughs Mountain, 500-420 thousand years ago
Burroughs Mountain, 500-420 thousand years ago. Click to expand.
Built during a very active eruptive period and some of the oldest lava flows in the park. Visible from the Sunrise Area.
Rampart Ridge, 380 thousand years ago
Rampart Ridge, 380 thousand years ago. Click to expand.
Began as a lava flow that formed against a wall of glacier ice, creating the steep lava cliffs visible from Longmire today.
Little Tahoma Peak, 160-40 thousand years ago
Little Tahoma Peak, 160-40 thousand years ago. Click to expand.
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.
Gibraltar Rock, 40-14 thousand years ago
Gibraltar Rock, 40-14 thousand years ago. Click to expand.
Rocks of many ages are exposed in the upper mountain features of Liberty Ridge, Willis Wall, Success Cleaver, and Gibraltar Rock.
Emmons Glacier Lava Flows, 2.2 thousand years ago
Emmons Glacier Lava Flows, 2.2 thousand years ago. Click to expand.
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.
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. This rock outcrop is visible along Mowich Lake Road (SR165), just outside the border of the park.
Ohanapecosh Formation, 36-28 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.
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.
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.
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.
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.
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.
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.
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.