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USGS Geology in the Parks

Domains of the North Cascades

FIELD TRIP STOP 7 - North Cascade Highway (State Route 20)

View of Crater Mountain from Highway 20, looking northwest
View of Crater Mountain from Highway 20, looking northwest.

Crater Mountain

Views of an ancient ocean floor

Travelers heading northwest on Highway 20 where it follows Granite Creek view the great mass of Crater Mountain rising 6,000 feet above the valley bottom of Canyon Creek. To enjoy the same view, however, east-bound travelers should stop at a the viewpoint and sign (located 11.6 miles from the Western Ross Lake Overlook; or 11.0 miles from Rainy Pass,) and look back the way they came.
Crater Mountain is carved from greenstone of the Hozomeen Terrane, once the basaltic floor of the ancient Methow Ocean. The mountain's name probably derives from the craterlike shape of its summit, which was carved from the ancient metamorphosed basalt by modern cirque glaciers. Crater Mountain is not a volcano with a summit crater. The rugged battlements of the greenstone viewed from the highway rest above phyllite of the Little Jack terrane, which is exposed in the lower slopes of the mountain. The thrust fault that separates the two terranes here was one of the first such faults discovered in the North Cascades by the late Peter Misch.
On to Easy Pass

Material in this site has been adapted from a book, Geology of the North Cascades: A Mountain Mosaic by R. Tabor and R. Haugerud, of the USGS, with drawings by Anne Crowder. It is published by The Mountaineers, Seattle.

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