Named for rocks in area of Green Mountain, lat 41 deg 07 min 30 sec N, long 106 deg 55 min 00 sec W, Carbon Co, WY, Northern Rocky Mountain region. No type locality designated. Overlies Archean quartz-biotite gneiss. Probably overlain by and intertongues with Big Creek Gneiss (new). Consists of several bodies of amphibolite grade metamorphic rocks consisting of sericitic, slabby, quartzite, siliceous marble, conglomerate, and felsic and mafic schists of volcanic origin. This formation records the first Proterozoic volcanism and sedimentation subsequent to intrusion of Baggot Rocks Granite in 2,560 m.y. and prior to intrusion of Sierra Madre Granite in 1,680 m.y. Characterized by poor exposures and scarcity of textures useful in determining bedding sequence and thus reconstructing the stratigraphy of the unit. Description of chemistry and petrology of units in formation. Geologic map. Is separated from Cow Creek Conglomerate (new), basal formation of Libby Creek Group by a structural unconformity. Assigned to the Proterozoic. Has an age of 1600 +/-200 m.y., an age that reflects the time of metamorphism a subsequent cooling associated with intrusion of Sierra Madre Granite. Has a minimum age of 1900 to 2000 m.y. based on relationship to other units.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Name applied to a series of calc-alkalic volcanic rocks and volcanogenic sedimentary rocks that may have formed near the edge of the Archean continent during Early Proterozoic time. Overlain by Libby Creek Group unconformably. Both sequences metamorphosed to the amphibolite facies and were isoclinally folded prior to 1,680 m.y. Geologic map of the Sierra Madre, WY, Northern Rocky Mountain region. Has a 1,600 +/-200 isochron.

Source: GNU records (USGS DDS-6; Denver GNULEX).