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MAP

Topo

Rock Formations

Measure

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Topo

Ecoregions

Public Lands

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BASEMAPS

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Temperature

Smoke

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WEATHER

Garnet Range Formation: locally includes upper Libby Formation and Pilcher Formation in northwestern Montana (MTYgr;0)

Geologic Formation in MT

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Lithology

Quartzite

Argillite

Geologic Age

Mesoproterozoic (1600 Ma – 1000 Ma ago)

Geologic Unit Label

Ygr

Dark green, micaceous, fine-grained quartzite with subordinate argillite interbeds. Thickness as much as 1,200 m (3,937 ft). In northwestern Montana - Libby Formation: Light to dark gray and greenish gray siltite and argillite with subordinate quartzite in mud-cracked couplets. Thickness as much as 2,300 m (7,546 ft). Pilcher Formation: Light gray and red cross-bedded, feldspathic, fine grained quartzite. Garnet Range Formation: Dark green, micaceous, fine-grained quartzite with subordinate argillite interbeds. Thickness as much as 1,200 m (3,937 ft).

— USGS

Taxonomy

Classified As

Geologic Formation