The lithology of placer gravels and indicators of glaciation were investigated in drainage basins near Mount Stewart, Thistle Mountain, and Selwyn Dome, west-central Yukon Territory. The composition of placer gravel indicates that mafic and felsic volcanic and subvolcanic rocks, unrecognized on existing bedrock geology maps, outcrop or suboutcrop in the area. Similar rocks host precious and base-metal deposits in the nearby Dawson Range.
Ultramafic rocks are more extensive in the study area than previously thought.
The presence of large erratic boulders suggests that the area may have been glaciated during the early Pleistocene.