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USGS Geology in the Parks

Terranes of the North Cascades Terranes of the North Cascades: Hozomeen Terrane

Location of Hozomeen Terrane rocks
Location of Hozomeen Terrane rocks shown in green.

Summary: Ocean-floor basalt, deep-ocean sandstone and shale, with lots of chert. Formed between 350 to 220 million years ago (Mississippian to Triassic).

The Methow Domain began as ocean floor formed between 350 and 220 million years ago (Mississippian to Triassic). The ocean floor was basalt overlain by some deep-ocean sandstone and mud, along with lots of chert. Some of the basalt erupted at a mid-ocean ridge, some erupted as oceanic islands like Hawaii, and some may have erupted as part of a volcanic island arc. We call this oceanic floor the Hozomeen terrane.

Location of Hozomeen Terrane rocks
Eruption of basalt in the ocean produces pillow basalt.

The rocks of the Hozomeen terrane do not fit well our bucolic description of the Methow scenery far from it. They stand out ruggedly in the high mountain ridge of Crater and Jack Mountains and peaks to the north.

Visit the Methow Terrane

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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