South Sister volcano viewed northward from the east shore of Sparks Lake.

The photo includes five rhyolitic units of different ages: Unforested 2-ka rhyolite of "Devils chain" rests on forested 35,000 year old flow lobe from adjacent Devils Hill dome. Three pale-gray spurs form sharp salients that extend to elevations only 550 m (1640 ft) below the darker andesitic summit of South Sister. Each spur is a petrographically distinctive rhyolite lava, and they yield ages of (from left to right) 51,000, 30,000–24,000 and 35,000 years old. On the skyline, South Sister summit and Hodge Crest are separated by the cirque of Lewis Glacier.