About north-northwest of the Franklin Glacier Complex is the deeply dissected Silverthrone Caldera. It is wide, with steep slopes extending from near sea level to a maximum elevation of . Like Franklin to the south-southeast, Silverthrone has not been studied in detail by scientists. As a result, its affinity and eruptive history is poorly known. It is considered to be part of the Garibaldi Volcanic Belt, but it also lies on the overlapping trend of the much older Pemberton Volcanic Belt. At least three phases of volcanic activity have been identified at Silverthrone. The first phase, following collapse of the caldera, deposited a thick sequence of undated basal breccia. It contains irregular subvolcanic intrusions, as well as a profusion of dikes. In some places, the basal breccia has been welded together by intense volcanic heat. Subsequent activity 750,000 to 400,000 years ago constructed rhyolite, dacite and andesite lava domes, breccia and lava flows. Mount Silverthrone, a volcanic peak associated with the Silverthrone Caldera, consists of overlapping andesite and rhyolite lava domes that were formed during this eruptive period. The third phase, less than 1,000 years ago, produced cinder cones, pyroclastic deposits and basaltic andesite lava flows that issued from vents on the rim of the caldera. Most of this activity occurred on the northern rim where lava flows traveled down the Pashleth Creek valley then into the Machmell River valley. The entire lava flow sequence is at least long, ranging in elevation from to . Many of the volcanic products are now buried under glacial ice. However, remains of cinder cones protrude through glaciers and lava flows are exposed at lower elevations, such as the extensive Machmell-Pashleth Creek lava flow. A relatively small basaltic andesite lava flow extends from the caldera's southern rim into the headwaters of the Kingcome River.