Stuart Range - Geology

Geology

The Mount Stuart batholith underlies the Stuart Range and the nearby Wenatchee Mountains. The batholith is about 13 by 16 miles in extent. Two plutonic masses are separated by a thin screen of Chiwaukum Schist and rocks of the Ingalls Complex. The more-eastern pluton is 93 million years old, while the more-western rock mass is between 83 and 86 million years old. Exposed rock tends to be quartz diorite and granodiorite.

The range sits near a convergent plate boundary where one plate overrides another. In Western Washington, the North American plate overrides the Juan de Fuca plate, resulting in both volcanic and seismic activity. This convergence has been ongoing for over 200 million years. Continuing uplift and erosion has exposed the underlying granite batholith, making for one of the more spectacular mountain ranges in Washington.