The Keweenaw Peninsula was very different in the past. About 1.1 billion years ago this area was much more active as there was rifting and the crust was pulling apart. This rift was found under what we now call Lake Superior. During this time extensive lava flows occurred as the crust was pulling apart releasing magma from the mantle to come to Earth’s surface. This lava was mafic and resulted in the basalt that is very wide spread around the Keweenaw Peninsula. However, during this time the enormous heat caused some of the continental crust to also melt. This resulted in a different type of lava being formed, that of felsic lava because the continental crust was higher in silica content than the lower mantle magma.
Later when this tectonic activity halted and the lavas finished cooling rock layers were formed. This isolated melting resulted in the formation of pockets of Rhyolite that were buried beneath the ground. Later around 1.04-1.08 billion years ago a compressional force was placed on the area due to the Grenville tectonic zone. This squeezing force caused an uplift of the underlying rock layers as much as 3-5 kilometers. Within these now lifted rock layers were the pockets of Rhyolite like the one you will find here at Bare Bluff. To learn more about the Keweenaw Fault