Silverthrone Caldera is the largest and best-preserved of the two caldera complexes in the northern Garibaldi chain, the other being the Franklin Glacier Complex to the east-southeast. The caldera has a diameter of and contains breccia, lava flows and lava domes. Like Franklin to the east-southeast, the geology of Silverthrone is poorly known due to minimal studies. The region surrounding the Silverthrone complex is significantly jagged due to the mountainous terrain of the Coast Mountains. Near vertical flanks extend from near sea level to more than in elevation. Silverthrone is significantly younger than the Franklin Glacier Complex to the east-southeast and its volcanics likely have ages comparable to other volcanics throughout the Garibaldi chain. The oldest volcanics at the Silverthrone Caldera complex are composed of volcanic breccias, some of which became fused together by intense volcanic heat from when the deposits were first erupted. After these volcanics were deposited, a series of dacite, andesite and rhyolite lava flows were erupted upon volcanic breccia from the first volcanic phase. These eroded lava flows in total are thick. Volcanics in the lower portion of this series of lava flows give a potassium-argon date of 750,000 years while volcanics slightly above the lava flows are 400,000 years old. The most recent volcanic activity produced a series of andesite and basaltic andesite lava flows down Pashleth Creek and the Machmell and Kingcome river valleys. The lava flow extending from near Pashleth Creek to down the Machmell River valley is over in length. Its small amount of erosion indicates that it could be 1,000 years old or younger.