The striking gullies that separate and define the three summits of the Chief are the result of fracturing and mass-wasting of large blocks along a series of vertical, and roughly north-south oriented deep seated fracture sets (joints).
The Chief may be the root of an extinct volcano because no volcanic activity has occurred in the Squamish area from about 86 million years ago to the beginning of Garibaldi Volcanic Belt volcanism about 2-3 million years ago.