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Grand Portage State Forest
Nearby Parks
State Park Information
State Park Overview
Nature of the Area
Mixed hardwood forest covers most of the park and is dominated by paper birch and quaking aspen, with occasional white spruce, white pine, balsam fir, white cedar balsam, poplar and
black ash. Visitors will also see mountain ash, mountain maple, red-dosier dogwood and
thimbleberry. The slopes and crest of the large ridge are boreal forest communities containing abundant groundcover that includes clintonia, bunchberry, wild sarsaparilla and
club mosses and ferns. The forested areas provide a beautiful backdrop to the rugged beauty of the falls and the shoreline of the Pigeon River that runs through the park.
The geology of high falls is a story of fire and ice. According to geologists, it begins in the middle of the Precambrian era about 1.9 billion years ago. An ancient sea covered what is now Minnesota and deposited mud that hardened over time into a layer of shales and slates known as the Rove Formation. These are the layered rocks you can see along the inside of the high falls gorge. About 1.2 billion year ago, the continent began to spread along a rift that extended from what is now eastern Lake Superior to Kansas. Basaltic lava flowed over this zone, while here in Grand Portage, database intrusions penetrated the older Rove Shales turning the contact area shales into slate. The cliff the falls run over is a diabase dike and is very resistant to erosion. Huge glaciers bulldozed away the softer rock (shale and slate) leaving the harder and more resistant rock (basalt) standing. There were four major advances of ice with warmer interglacial climates between each advance. We are currently in the fourth interglacial period with the most recent glacial retreat having occurred around 10,000 years ago. The land around the Lake Superior basin gradually rebounded from the weight of the ice and the lake level slowly receded. The ridges around Grand Portage State Park would have first emerged as an isolated group of offshore islands. As centuries passed, gravel was deposited in terraces by the retreating lake. The path to High Falls cuts directly through one of these gravel terraces. About 9,000 years ago, the lake level dropped to a point where the river mouth would have been at the lower end of the High Falls gorge. If High Falls is a post-glacial landform, then the gorge is only about 9,000 years old. There is speculation among geologists that the gorge was cut before the glaciers came, filled with sediment and
was re-excavated after the lake level dropped. There is evidence for this happening in several other North Shore river valleys.
The glacial ridges in the park add to a varied terrain which harbors an abundance of wildlife. The channeled bays and river islands below the falls are home to osprey, eagle, otter, beaver, moose and
great-blue heron. Visitors can expect to see white-tail deer and black bear along with other small animals and birds.
History of the Area
More Info
Grand Portage State Forest