The great ice ages that began about one million years ago were characterized by the advance and recession of huge ice sheets over vast areas of North America. These continental glaciers, originating in Canada, moved southward, scraping up mantle . . . — — Map (db m252767) HM
Of all the geological agents which have played a part in shaping the face of Minnesota, the most overwhelming and powerful one is glacial ice. At least four times during the last million years, continental glaciers have spread over the state . . . — — Map (db m101379) HM
This point overlooks the St. Louis River Valley. The steeply inclined rocks in the river channel upstream are alternating beds of slates and graywackers of the Thompson Formation thousands of feet thick.
. . . — — Map (db m44627) HM
Toward the end of the great ice ages about 10,000 years ago, the glacier, which had pushed its way along the trough of Lake Superior, retreated toward the northeast, and near Moose Lake crossed the divide between the Mississippi River and Lake . . . — — Map (db m205057) HM
Two kilometers northwest of here, the St. Louis River flows on its way to Lake Superior. Its broad river valley, visible from this point, is in a western extension of the Lake Superior basin. Over the last two million years, the Lake Superior basin . . . — — Map (db m205010)
About 1.1 billion years ago, a great rift valley formed across the North American continent from the Lake Superior region southwest to Kansas. As this rift valley opened, basaltic lavas erupted into it, accumulating to a thickness of up to 20 . . . — — Map (db m45814) HM
The potholes at the St. Croix Dalles have their origins in a tale of fire and ice. They are carved in a dark volcanic rock called basalt, which erupted as lava 1.1 billion years ago. This basalt is related to lava flows that line the North Shore of . . . — — Map (db m46434) HM
Toward the close of the last or Wisconsin stage of glaciation about 10,000 years ago, the ice front receded from central Iowa toward the north and, in the latitude of Browns Valley, crossed the continental divide between the Mississippi River and . . . — — Map (db m233564) HM
The diversified scenery of Minnesota- of which the Itasca park area is one phase- is due to the location of the state in the approximate center of the continent, situated midway between the Atlantic and Pacific oceans, Hudson Bay and the Gulf of . . . — — Map (db m232172)
The rocks of the North Shore of Lake Superior record the last period of volcanic activity in Minnesota. This volcanism occurred 1.1 billion years ago when the North American continent began to rupture along a great rift valley, which extended from . . . — — Map (db m203069) HM
The harbor of Grand Marais is the result of unequal weathering or erosion of two types of rock. One of these, called diabase, resulted from the cooling of molten material which was forced between two earlier lava flows. The dark, massive diabase, . . . — — Map (db m203155) HM
Toward the close of the Wisconsin stage of glaciation about 12,000 years ago, the waning lobe of the ice sheet in the Brainerd area retreated westward, leaving in its wake many stagnant ice blocks which had become separated from the main ice field. . . . — — Map (db m155678) HM
The Portsmouth was one of many iron and manganese mines that operated along the Cuyuna Range during the period 1911-1978. As much as 60 meters of glacial sediment cover the iron-bearing bedrock in this area; there are few natural rock exposures. . . . — — Map (db m277208) HM
Hasting lies just south and East of the last glaciation. About 20,000 years ago a lobe of ice, called the Superior lobe, advanced from the Lake Superior basin and crossed the ancient bedrock valley of the Mississippi River between St. Paul and . . . — — Map (db m42199) HM
During the great ice ages the landscape of Minnesota was profoundly altered by continental glaciers in four major epochs of glaciation. In this area, as elsewhere, the closing stage of each epoch was characterized by the release of floods of . . . — — Map (db m45869) HM
Like most lakes in Minnesota, Lake Minnetonka was formed during the Ice Age of the last two million years. During several separate glacial periods, ice advanced along different routes across the state. The glaciers, along with large volumes of . . . — — Map (db m59925) HM
Near Fort Snelling, 10,000 years ago, melt water from the Wisconsin glacier was discharged through the Mississippi River and plunged over a ledge of Platteville limestone into a gorge cut chiefly in the white St. Peter sandstone. The . . . — — Map (db m40765) HM
The continental glaciers spreading over Minnesota during the great ice ages brought vast quantities of rock material from the north to be dumped indiscriminately during the recession of the ice. Old river valleys were filled and belts of . . . — — Map (db m37863) HM
The agricultural land of the Willmar region has a history that dates back 60 million years, when an inland sea covered the Great Plains from the Gulf of Mexico to the Arctic Ocean. As the adjacent land eroded and life in the sea flourished, . . . — — Map (db m75844)
The scenery of the region between Split Rock and Beaver Bay is the direct result of important events of early geologic time.
Lava flows, which had accumulated in this region to a thickness of about 30,000 feet, were lifted and arched by a . . . — — Map (db m76280)
Earth's Crust Ruptures
The geology of the shoreline between Split Rock and Little Marais is the direct result of cataclysmic events that occurred many kilometers* below the earth's surface. About 1.1 billion years ago, this continent began . . . — — Map (db m204164) HM
As you walk the pebbled beaches of the North Shore, watch for translucent, color-banded, and reddish-brown stones called Lake Superior agate—Minnesota's state gemstone. The story of the Lake Superior agate begins 1.1 billion years ago, when basaltic . . . — — Map (db m204248) HM
The classic steel arch bridge that spans this gorge is impressive for its simple beauty and elegance. Equally remarkable, but not as obvious to the onlooker, is the massive underground foundation that keeps this bridge sound and secure. To construct . . . — — Map (db m204424) HM
The second highest point in southwestern Minnesota is about one kilometer north of here on the Bemis moraine, locally known as Buffalo Ridge. This ridge marks a drainage divide separating the watersheds of the Mississippi and Missouri Rivers. Lake . . . — — Map (db m228133)
This marker is located near the big bend of the Minnesota River directly opposite the mouth of the Blue Earth River. The abandoned channel east of it is the former course of the LeSueur before it joined the Blue Earth. Most of the broad . . . — — Map (db m66715) HM
The diversified scenery of Minnesota - of which the Rochester area is one phase - is due to the location of the state in the approximate center of the continent. Situated midway between the Atlantic and Pacific Oceans, Hudson Bay and the Gulf of . . . — — Map (db m178698) HM
This point commands a view of one of the great water courses of North America. The stream which once filled this valley, named the River Warren, was larger than any river on the continent to-day.
During the past million years, Minnesota has . . . — — Map (db m225300) HM
Exposed in the rocky hillocks of the Minnesota River valley between Montevideo and Morton are some of the oldest rocks on earth. The pink-and-black banded rock used for the pedestal of this tablet is a metamorphic rock called gneiss (pronounced . . . — — Map (db m69216) HM
Lake Superior is situated over the Midcontinent Rift, which is a rupture in the North American continent that formed a great rift valley from the Lake Superior region southwest to Kansas about 1.1 billion years ago. For about 20 million years as the . . . — — Map (db m5113) HM
The Laurentian Divide separates the watershed of streams that flow north to the Arctic Ocean from the watershed of streams that flow south through the Great lakes to the Atlantic Ocean. Where you are standing the divide is formed by a prominent . . . — — Map (db m183138) HM
Minnesota was largely covered by glaciers many times during the last million years. The ice flowed across the state from both the northeast and the northwest. As it advanced along separate paths, it scraped up, crushed, and carried with it . . . — — Map (db m69965) HM
Lake Pepin occupies the Mississippi Valley above this point for a distance of 22 miles. The lake is formed by the delta of the Chippewa River which enters the Mississippi directly east of this site.
The Chippewa, a relatively small river, has a . . . — — Map (db m45700) HM
The site of this tablet marks the northern limit of Lake St. Croix, impounded by the natural dam of sand and gravel, made by the Mississippi where it is joined by the St. Croix River, twenty miles below Stillwater. The valley, with its steep . . . — — Map (db m233569) HM
From Winona to La Crosse, the Mississippi River valley displays its greatest depth as it extends vertically through more than 240 meters of a sedimentary-rock plateau. Here, Highway 61 follows the narrow strip between the river and the steep bluffs . . . — — Map (db m213346) HM
The bold and picturesque bluffs of the Whitewater Valley, from the Jordan sandstone below to the massive Oneota dolomite at the top, represent deposition during a hundred million years. Much of the erosion of these marine sedimentary rocks occurred . . . — — Map (db m213348) HM
In its traverse of 2400 miles from Lake Itasca to the Gulf of Mexico, the Mississippi River falls 1475 feet, nearly two-thirds of which is within or along the eastern side of Minnesota. For 300 miles from Minneapolis, its course lies between rocky . . . — — Map (db m166631)
