Mount Garibaldi is known both for the very high quality exposures of its internal structure and for its conspicuous topographic anomalies, which can be attributed to the growth of the mountain onto a large glacier system and the subsequent collapse of the flanks of the volcano with the melting of the ice. The western flanks of the mountain expose basement rocks, sheared and altered quartz diorite, carved by streams and glaciers into a rugged topography with relief up to . Valleys in this jagged surface have been filled with 0.52 to 0.22 million year old dacite and andesite flows, tuff breccias, and domes, precursors of the activity at Mount Garibaldi. About of material remains in the volcano. In modern times, the apron of material around the volcano's main vent extends at least from its source in places that were covered by ice. In other areas its extent is less and its slope is steeper.