The Dinner Creek Tuff is a mid-Miocene rhyolitic to dacitic ignimbrite, consisting of four cooling units with 40 Two volcanic centers related to the Dinner Creek Tuff were identified. The southern volcanic center, centered at Castle Rock, is a caldera and source of the Dinner Creek Tuff unit 1 (DIT1). Rheomorphic, densely welded DIT1 is over 300 m thick along the east side of Castle Rock. The northwestern margin of the caldera has been uplifted along faults, showing vertically foliated tuff dikes and associated mega-breccia deposits.Up to 200 m of incipiently welded tuffs, and fluvial volcaniclastic sediments were deposited on the caldera floor, which has been uplifted due to resurgence and regional extension, creating the complex structural relationships between the volcanic units.The northern volcanic center is located at Ironside Mountain, where densely welded rheomorphic Dinner Creek Tuff unit 2 (DIT2) is exposed in outcrops over 600 m thick.