The Montana Mountain area lies at the western edge of the Intermontane Belt, where the Whitehorse Trough overlies the Atlin Terrane. Paleozoic volcanic rocks of Atlin Terrane and clastic rocks of the Laberge Group occur along the margins of the area mapped. Cretaceous intermediate volcanic rocks of the Mount Nansen Group intrude this basement within a roughly circular area about 7 km in diameter and are referred to as the Montana Mountain Volcanic Complex. The northern margin of the complex is metamorphosed by a granite pluton related to the Coast Plutonic Belt. Porphyritic rhyolite dikes intrude the Mount Nansen Group and adjacent Laberge strata.
Quartz veins, some with economic mineralization, cut the granite and Mount Nansen volcanic rocks. Although Montana Mountain has a long history of prospecting and mining ventures, no detailed study of the geology is generally available.
