The BorderWaters region is a beautiful landscape where rocks wilderness and water reflect the depth of time and the formation of a continent. The rock formations of the BorderWaters region have fascinated people for millennia. Exploring jagged, vertical slabs of ancient fault-sheared greenstone or quietly following mysterious rock cairns over smooth, ice scratched, granite, whalebacks can provide days of adventure, fun, and wonderment about the geologic processes that so dramatically shaped this landscape. In fact, one of the defining concepts influencing the formation of Voyageurs National Park was the geologic formations and exciting geologic history of the area.

The depth of time the rocks represent is truly mind boggling. Most of the bedrock in the BorderWaters region formed between 3.0 and 1.0 billion years ago. Most noticeable when traveling the lakes and highways of the region are vertical slabs of rock commonly called greenstone. These rocks are primarily volcanic in origin, however, the green color is a product of later heat and pressure, due to deep burial under towering mountain ranges colliding continents, and the ominous presence of ancient bodies of molten magma.

The geologic story of the region is beset by the slow conflagration of moving and shifting continents, the opening and closing of ancient ocean basins, and finally the last of the great ice ages. The BorderWaters region and everything north is commonly referred to as the Canadian Shield. The Canadian Shield is at the core of the North American Continent and represents the first stage in the formation of North America as we know it. It was assembled slowly, over billions of years by the mighty process of plate tectonics. In this sense the Canadian Shield is composed of numerous flakes and fragments of older continents and chains of volcanic island arcs - much like the Aleutian islands of northwest Alaska. These continents and island arcs form linear, roughly parallel chains or belts of Precambrian rock that were literally squashed together over time. Geologists call them greenstone belts and can regale the unsuspecting visitor with hours of delightfully vivid descriptions of what the landscape looked like and how it has changed through time.

To get an idea, visualize yourself wielding an immense continent-sized saw. Begin by placing the saw in an east-west orientation, say from Baudette, Minnesota to Thunder Bay, Ontario, and methodically slicing the Border Waters region and the rest of the Canadian Shield into bands about 200 miles or so in width. Each of these bands would represent an ancient micro-continent or line of volcanic islands, similar to say Japan, the Philippines, or the Aleutians. Now spread the bands apart from north to south and watch the worlds oceans fill in the spaces. In these new, or rather old, oceans, sediments are accumulating. After a time, starting in the north, systematically push the bands of rock back together. Watch as the ocean sediments squeeze up between, to become what we presently call biotite schist. If you use enough force, the belts of rock will also fold and crumple upwards to form towering coastal mountain ranges, bordering the slowly closing seas. Each time two bands of rock collide, you are creating one of the many mountain building events to have influenced the region. With the pressure you are exerting, the ocean floor underneath many of the oceans will be forced beneath the continental crust (it has to go somewhere) and as it dives deeper will melt. This melting rock will rise as magma and either cool in place to form the bodies of cliff-making granite that lend this landscape so much of its drama, or will erupt as lava through volcanoes at the surface. In essence the ancient Border Waters region was a dramatic, and often violent landscape replete with volcanoes, oceans, towering Andes or Himalayan-style mountain ranges, and major, often, San Andreas-type fault zones.

But where are they now. Today the topography of the region is more or less tame. The answer lies in time and weathering. By about 2 billion years or so the BorderWaters Region was at peace. Most of the action was taking place to the south east and west. Over the next two billion years, time begin to take its toll. Weathering and erosion slowly wore down the mountains. Today, when traveling the BorderWaters region we traverse the roots of ancient mountains and, if traveling north to south have the opportunity to visit the remains of multiple ancient continents. Another way of looking at it is, if traveling from Minnesota northward into Canada, you would literally be walking backward through time.

The final chapter in this story begins about two million years ago with the last great ice age. With cooling temperatures, ice invaded from the north, covering the Border Waters region in mighty glaciers. As you might imagine this was erosion at its best. The weakened fault-rock was most easily eroded and plucked-up by the moving ice sheets, to create low-lying basins, later to fill with glacial melt water. This is the origin of our beautiful scenic lakes, and indeed, many of the original rocks can now be found in southern Minnesota and northern Iowa. The harder granite was more or less left in place but often sculpted into the magnificently smooth whale-back shaped islands and headlands which define many of the lakes. One of the most diagnostic features of our post-glacial landscape one might notice are peculiar rounded boulders which simply don’t belong here. They come from far to the north, and were transported south by the glaciers. These round travelers are called glacial erratics and add beauty and surprise to the surroundings. To the unwary traveler they always seem slightly out of place, and thus are easy to recognize. The ice, eventually begin to melt, and by 10,000 years ago was gone, leaving behind scratches and scouring on smoothed rock outcroppings, bountiful lakes, and of course the erratics.

As you travel through the BorderWaters region, keep a sharp eye out for the famed greenstone. It is really the eroded remnants of ancient volcanoes. Watch for pink and white crystalline granite and know that you are seeing the now cold, frozen evidence of liquid-hot magma that cooled deep beneath our ancient mountains. The gray to black outcrops, sparkling with brown biotite mica are really what is left of the buried ocean sediments squished between colliding continental fragments. And finally don’t forget to keep a sharp eye out for north to north-east elongated, glacial scratches in the rocks, and those strange looking, round boulders that just don’t seem to belong in this region of jagged greenstone and massive granite cliffs.

When in the BorderWaters region, remember, most every rock you encounter, if you listen carefully, can tell you a story. It is a story of a continent awash with dynamic seas, great uplifting mountainous events, colliding continents, volcanic desolation, peaceful erosion, deep blue ice, far reaching lakes, and finally the lush growth of forests, wildlife, and human culture. So follow the mysterious cairns through this ancient, storied landscape of rocks, ice, and Border Waters.

written by:
Chris Hemstad