Also known as: South Twin Sister, North Twin Sister
The Twin Sisters are a striking pair of dunite peaks west of Mount Baker offering excellent ski touring and mountaineering. South Twin is the higher and more frequently climbed summit, with a straightforward approach through forest and across open slopes. The unusual dunite rock gives the peaks a distinctive reddish-orange hue.
The Twin Sisters are composed of dunite — an ultramafic rock rarely found at the surface — making them geologically unique in the Cascades. The dunite supports unusual plant communities adapted to the magnesium-rich, calcium-poor soils.