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Green Mountain Laccolith (Little Sundance Dome) (Sundance, Wyoming, USA) 1 | by James St. John
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Green Mountain Laccolith (Little Sundance Dome) (Sundance, Wyoming, USA) 1

Green Mountain - an igneous laccolith in the Eocene of Wyoming, USA.


Several igneous intrusions occur in the vicinity of the town of Sundance in northeastern Wyoming. The intrusion shown above is Green Mountain. Igneous rocks are not exposed at the surface here - the hill consists of Minnelusa Formation sedimentary rocks (Pennsylvanian-Permian in age). Those rocks have been altered by heating as a result of the intrusion of an underlying, Eocene-aged igneous laccolith. Laccoliths are lens-shaped igneous intrusions. The Green Mountain intrusion is circular in map view.


Locality: Green Mountain (also known as Little Sundance Dome), 2 to 3 miles east of town of Sundance, southeast-central Crook County, northeastern Wyoming, USA


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Taken on August 4, 2015