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Home Archived Aug 4, 2016

USGS Geology in the Parks

Domains of the North Cascades

SIDE TRIP E - Great hike off the North Cascade Highway (State Route 20)

Maple Pass

View from Maple Pass area View east from above Lake Ann. Mountains on the far side of Granite Creek and beyond the dashed contact line are carved from granite of the Golden Horn batholith. Dotted line is hidden contact behind Whistler Mountain. Foreground ridges are in tonalite of the Black Peak batholith.

Views of a wandering batholith

Black Peak
Black Peak from trail to Maple Pass.

Hikers who have reached the high point (6,980 feet) between the Lake Ann and the Rainy Lake cirques, not only have terrific views in all directions, but can contemplate two batholiths, one a foreign immigrant, and one a native Washingtonian. Black Peak and its attendant ridges display cliffs and glacier-sculpted ridges, known as aretes. Orange and yellow peaks rise to the east, across Granite Creek valley and the highway. The dark-hued mountains are eroded from the tonalite and quartz-diorite of the Black Peak batholith; and the orange-to-yellow peaks, from the granite of the Golden Horn Batholith. Black Peak magma invaded the surrounding rocks of the Chelan Mountains Terrane about 90 million years ago (Cretaceous), but the Golden Horn granite intruded only about 45 million years ago (Eocene). Some geologists believe that the Chelan Mountains terrane may have been located far to the south when it was invaded by Black Peak magma, but was more or less where it is today by the time Golden Horn magma rose up into it.

On to Washington Pass Overlook

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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