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Home Archived Aug 4, 2016

USGS Geology in the Parks

field trip map 3

FIELD TRIP SIDETRIP I - off Mount Baker Highway (State Route 542)

Yellow Aster Meadows

Yellow Aster
View of stacked thrust plates on thick faulted slab of Yellow Aster gneiss holding up Yellow Aster Meadows (looking southwest from near Yellow Aster Butte).

Home of the Yellow Aster Complex

In the Yellow Aster Meadows area, west of Yellow Aster Butte, travelers hike on a great slab of old gneiss of the Yellow Aster Complex. This fault-bounded block, some four square miles in area, is one of many in the Bell Pass mélange, though some blocks are only a few feet across. Where the rough and steep trail reaches the open undulating country of the meadows and threads around bumps of gneiss and small ponds, look west to a rounded high knob of stacked thrust plates. Above the highly smashed gneiss holding up the meadows and ponds is a faulted layer of ocean deposits--chert and shale about 225 million years old (Triassic)--that are also part of the Bell Pass mélange. Above the chert and shale is Darrington Phyllite, another ocean-bottom deposit, about 150 million years old (Jurassic). Darrington Phyllite is part of the Easton terrane. Miners' diggings here and there in the Meadows are generally into pods of dark green serpentine, metamorphosed blocks of the Earth’s mantle that have been dragged into the Yellow Aster gneiss along faults. The prospectors probably hoped to find nickel deposits, which are not uncommon in ultramafic rocks. They may have found some nickel ore, but unfortunately the miners knew nothing of mélanges, and did not realize that the small blocks they were digging in did not contain enough ore to make them rich.
On to Twin Lakes Road

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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