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WEATHER
Quadrant and Amsden Formations (MTPAMqa;0)
Geologic Formation
in
MT
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ID
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Lithology
Sandstone
Limestone
Shale
Other
(148 mi²)
Geologic Age
Serpukhovian – Moscovian (331.1 Ma – 307.1 Ma ago)
Geologic Unit Label
PAMqa
Quadrant Formation (PAq): Very light gray, yellowish or pinkish, well-sorted sandstone or quartzite, locally interbedded with subordinate limestone beds. Marine. Generally, thickness as much as 140 m (460 ft), but as much as 800 m (2,625 ft) in southwestern-most Montana. Amsden Formation (PAMa): Red shale, light gray limestone, and cherty and sandy limestone. Coastal plain or marine. Thickness as much as 180 m (590 ft).
—
USGS
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Geologic Formation
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