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FIELD TRIP SIDETRIP J - Twin Lakes Road off Mount Baker Highway (State Route 542)

Twin Lakes Road

Last whack
A last whack of thrusting shuffles the usual pile of thrust plates.

Cutting the deck

spacer image Beyond Gold Run Pass Trailhead, the road to Twin Lakes is a private mine road, a tentacle of civilization into the Mount Baker Wilderness. Many years, the road is closed by mud slides and snow-avalanche debris, but most summers, the mine owners or friends of Twin Lakes open the road--sort of. All but four-wheel drive vehicles generally must be parked near the Forest Service trail to Gold Run Pass and Tomyhoi Lake. From the road, but beyond the Gold Run Pass Trail junction, look up slope to cliffs of dark phyllite, a layer of Darrington Phyllite (Easton terrane) sandwiched between thrust plates of volcanic rocks of the Chilliwack River terrane. Throughout most of the Western Domain, the Chilliwack River terrane lies below the Easton terrane, but not both above and below the Easton terrane, as is the case here. Such a glaring exception to the structural order might destroy the faith of any geologic acolyte. But as shown in the drawing here, the anomalous stacking is simply the result of subsequent thrust-faulting that cuts across the deck of previously stacked terranes.

On to Twin Lakes
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This site is a cooperative endeavor of the
US Geological Survey Western Earth Surface Processes Team
and the National Park Service.
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This page was last updated on 11/30/99

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