Nature & Science

Rove Formation graywacke
Foreground: Broken rock slabs of a type of sandstone known as graywacke (gray'-wacke). Background: Layered cliff of the 1,750 million (1.8 billion) year old Rove Formation. The layered cliffs are the source of the broken graywacke slabs which mostly erode through frost cycles. When blocks fall, they tend to break parallel to the layering.

NPS Photo / Mike Plummer-Steen


Grand Portage National Monument is listed on the National Register of Historic Places as nationally significant for its, "…association with the fur trade and exploration and colonization of the northwest, its historic/geographic link between the United States and Canada, and its excellent state of preservation in a semi-wilderness setting."

The monument preserves 710 acres which includes: the historic depot (71 acres) located on Lake Superior, the site of Fort Charlotte (98 acres) on the Pigeon River with the Grand Portage (541 acres) connecting the two depots. The 8.5 mile portage corridor and Fort Charlotte (639 acres) contain the majority of the Monument's semi-wilderness setting.

Furrowed bark and evergreen tree foliage
Majestic old growth eastern white pine along the Grand Portage.

NPS Photo

Plants: The historic Grand Portage footpath preserves an important component of the largest terrestrial ecosystem in the world, the boreal forest (the Laurentian Mixed Forest Province of Minnesota). This forest of evergreen and broadleaf trees encircles the earth below the treeless tundra of the polar north and above the broadleaf forest to the south.

Grand Portage Diabase Dike
About 20 weather resistant dikes of the 1,100 million (1.1 billion) year old Grand Portage Diabase Complex have been recognized in the region.  If they reached the surface, basalt flowed out.

NPS Photo / Mike Plummer-Steen

Geology: Rugged hills and boggy lowlands, shear rock cliffs, shallow incised bays and Lake Superior, all come together in the highlands of Grand Portage. This extraordinary and impressive landscape was created by the different weathering rates of two types of rocks produced during Precambrian time. For nearly one billion years, stream erosion and glacial scour have removed much more of the soft than the hard rock leaving a modern relief of more than 600 feet.

Ridges have formed on a coarse, dark, resistant rock known as diabase (di′-a-base); lowlands and bays were produced in softer rocks of graywacke (gray′-wacke) sandstone and shale. The Grand Portage and Mt. Rose trails cross the highland regions which provide panoramic views of one of lowland areas, Grand Portage Bay.

Last updated: April 10, 2015

Contact the Park

Mailing Address:

P.O. Box 426
Grand Portage, MN 55605


(218) 475-0123

Contact Us