Voyageurs National Park is situated on the southern tip of what is known as the Canadian Shield, a gigantic dome of volcanic bedrock that forms the heart of the North American Continent. This bedrock dates from the birth of North America. Some 2.8 billion years ago, massive volcanoes erupted through this area and deposited layer after layer of ash and lava, building up the island landmasses. These island arc volcanoes collided forming still larger landmasses. Subsequent uplifting, folding, superheating along with tremendous pressure created igneous and metamorphic rock to form the present day granite and schist of the Kabetogama Peninsula. Eons of erosion then wore down these volcanic mountain ranges to the landscape you see today. 

Visiting Grassy Bay Cliffs 

The sheer granite cliffs of Grassy Bay rise 125 feet above the surface of Sand Point Lake and reach one of the highest points within Voyageurs. This Lac La Croix biotite granite batholith (a body of magma that cooled underground) is the largest and youngest igneous intrusion in the area, dated at 2.64 to 2.69 billion years old. 

In summer, these cliffs are accessible by boat and in winter by snowmobile. There are currently no amenities at this Visitor Destination.