Mont Saint-Bruno might be the deep extension of a vastly eroded ancient volcanic complex, which was probably active about 125 million years ago.A Hundred-Million Year History of the Corner Rise and New England Seamounts Retrieved on 2007-08-01 The mountain was created when the North American Plate moved westward over the New England hotspot, along with the other mountains of the Monteregian Hills. As a result, Mont Saint-Bruno forms part of the Great Meteor hotspot track. Its igneous rock consists mostly of pyroxenite and gabbro.
