The Mount Garibaldi map-area is in the southern part of the plutonic complex comprising the Coast Mountains of British Columbia.
The oldest rocks of the map-area are metavolcanic and minor metasedimentary rocks of unknown age and structure. These are extensively invaded by a quartz diorite batholith, the earliest of the plutonic masses, which displays an unfoliated core, a margin with highly developed secondary foliation, and an intervening zone of primary foliation. Bedded rocks at least 20,000 feet thick, principally clastic sediments derived in part from the batholithic rocks, occur in fault blocks north of Garibaldi Lake. The rocks of one fault block rest uncomformably on the older quartz diorites and contain Upper Cretaceous fossils; those of the other fault blocks are thought to be slightly younger than the fossil-bearing beds. The bedded rocks have in turn been invaded by later quartz diorites which are partly contemporaneous with and partly later than the block faulting. Two post-tectonic and presumably post-Upper Cretaceous batholiths lie partly within the map-area.