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USGS Geology in the Parks

field trip map 3

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

Twin Lakes

crinoid stems
Crinoid stem fossils in block of Chilliwack limestone.

Ancient volcanic rocks and a glacial pass

Twin Lakes are glacial tarns nestled in a U-shaped glacier-carved pass. The brown and rubbly rocks rising up from the evenness of the pass are volcanic rocks of the Chilliwack River terrane, and with a bit of looking, visitors can find fragments or pods of light grey, roughened limestone. Light-colored outcrops on the hillside, which contrast with the darker volcanic rocks, may be the same material. Some of these pods in the volcanic rocks have fossils (see also fieldtrip stop 1). The volcanic rocks themselves are so altered by metamorphism that on close approach they are rather nondescript and unattractive even to a geologist.
On to Lone Jack Mine
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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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