The mountains are made of schist, part of the Nason terrane. The original rock in the Nason terrane was laid down 210 Myr ago. The terrane then smashed into the western coastline of the continent, and the Mount Stuartbatholith intruded into it in the late Cretaceous. The intrusion of the granitic rock metamorphosed the rock into schist. [1].
The Chiwaukum Mountains and Larch Lake, looking southeast.
