South Sister's northwest summit, basaltic andesite lava and scoria cap the volcano.
Lost Creek Glacier and its cirque are in the center, and Eugene Glacier and its cirque are toward the bottom left. Fingerlike lobes of dacite lava dribble down northwest ridge atop fragmental deposit and beneath capping agglutinate. The entire edifice visible here was built between 30 and 20 ka.
Hildreth et al., 2013