View northwestward of South Sister volcano and unforested "Devils Chain" rhyolite lava domes.

The "Devils chain" is a string of nearly contiguous, virtually uneroded rhyolite lava domes and flows aligned north-south along a 5 km (3 mi) stretch on the southeast apron of South Sister. The largest of these is the Newberry flow (right center, below South Sister), only 2.5 km (1.5 mi) from the summit of South Sister. These rhyolite lavas were erupted about 2,000 years ago, during the most recent eruptive episode at South Sister, which also ejected pumice fall that still mantles much of the area.