As a stratovolcano, the Mount Cayley massif is built up of solidified lava and ash from successive volcanic eruptions. It is predominantly dacitic in composition, although rhyodacite is also common. Its original and current volumes remain uncertain. It may have had a volume as large as , but erosion has since reduced it to glacially eroded crags. The modern volcano has an estimated volume of and is only a modest fraction of its total output of silicic eruptive products. It has a proximal relief of and a draping relief of , with a nearly vertical cliff more than high immediately above the Turbid Creek valley.[a] Turbid Creek, Dusty Creek, Avalanche Creek and Shovelnose Creek flow from the slopes of the Mount Cayley massif.