Bachelor

This volcanic system extends from Mount Bachelor on the N to Lookout Mountain about 20 km S, with a chain of scoria cones and small shield volcanoes between and additional volcanic features to the E. The basaltic andesite and basaltic volcanoes formed during four eruptive periods dating back to about 18,000-15,000 years before present (BP). Construction of the main scoria cone chain was completed by about 12,000 years BP, and Bachelor (formerly known as Bachelor Butte) is one of its youngest features.

The latest activity produced lava flows on the E side of Sparks Lake from scoria cones on the NNE flank of Bachelor, and lava flows from Egan scoria cone on the N flank that slightly preceded the eruption of the Mazama ash from Crater Lake about 7,000-8,500 years ago.