To the northwest, the Franklin Glacier Complex is a set of volcanic bedrock that encompasses an area long and wide. It has an elevation of over and is largely destroyed by erosion. A series of dikes and subvolcanic intrusions compose the complex, a few of which seem to represent vents for the overlying sequence of volcanic deposits. Volcanics include dacite breccia and small remnants of hornblende andesite lava flows associated with tuffs that reach thick. The complex is poorly known due to minimal studies, but potassium-argon dates obtained from some of the subvolcanic intrusions indicate that Franklin formed during two volcanic events, each separated by about five million years of dormancy. The first event occurred between six and eight million years ago when volcanic activity in the Garibaldi Belt had not moved to its current location, but was becoming more aerially restricted within a large band to the east and west. During this period, volcanic activity in the Garibaldi Belt and other portions of the northern Cascade Arc took place mainly at the Franklin Glacier Complex and in the Intermontane Belt further east. When the Garibaldi Belt moved to its current location five million years ago, another volcanic event occurred at the Franklin complex. This final and most recent volcanic event occurred between two and three million years ago, about a million years after Mount Cayley to the south began its formation.