Geology

Geology

Main article: Geology of Minnesota

See also: List of lakes in Minnesota and List of Minnesota rivers

Tilted beds of the Middle Precambrian Thomson Formation in Jay Cooke State Park^[15]

Minnesota has some of the Earth's oldest rocks, gneisses that are about 3.6 billion years old (80 percent as old as the planet).^[15][16] About 2.7 billion years ago, basaltic lava poured out of cracks in the floor of the primordial ocean; the remains of this volcanic rock formed the Canadian Shield in northeast Minnesota.^[15][17] The roots of these volcanic mountains and the action of Precambrian seas formed the Iron Range of northern Minnesota. Following a period of volcanism 1.1 billion years ago, Minnesota's geological activity has been more subdued, with no volcanism or mountain formation, but with repeated incursions of the sea, which left behind multiple strata of sedimentary rock.^[15]
In more recent times, massive ice sheets at least one kilometer thick ravaged the landscape of the state and sculpted its terrain.^[15] The Wisconsin glaciation left 12,000 years ago.^[15] These glaciers covered all of Minnesota except the far southeast, an area characterized by steep hills and streams that cut into the bedrock. This area is known as the Driftless Zone for its absence of glacial drift.^[18] Much of the remainder of the state outside the northeast has 50 feet (15 m) or more of glacial till left behind as the last glaciers retreated. Gigantic Lake Agassiz formed in the northwest 13,000 years ago. Its bed created the fertile Red River valley, and its outflow, glacial River Warren, carved the valley of the Minnesota River and the Upper Mississippi downstream from Fort Snelling.^[15] Minnesota is geologically quiet today; it experiences earthquakes infrequently, and most of them are minor.^[19]

Palisade Head on Lake Superior formed from a Precambrian rhyolitic lava flow.^[15]

The state's high point is Eagle Mountain at 2,301 feet (701 m), which is only 13 miles (21 km) away from the low of 601 feet (183 m) at the shore of Lake Superior.^[17][20] Notwithstanding dramatic local differences in elevation, much of the state is a gently rolling peneplain.^[15]
Two major drainage divides meet in Minnesota's northeast in rural Hibbing, forming a triple watershed. Precipitation can follow the Mississippi River south to the Gulf of Mexico, the Saint Lawrence Seaway east to the Atlantic Ocean, or the Hudson Bay watershed to the Arctic Ocean.^[21]
The state's nickname, the "Land of 10,000 Lakes", is apt, as there are 11,842 Minnesota lakes over 10 acres (4 ha) in size.^[22] The Minnesota portion of Lake Superior is the largest at 962,700 acres (389,600 ha; 3,896 km²) and deepest (at 1,290 ft (390 m)) body of water in the state.^[22] Minnesota has 6,564 natural rivers and streams that cumulatively flow for 69,000 miles (111,000 km).^[22] The Mississippi River begins its journey from its headwaters at Lake Itasca and crosses the Iowa border 680 miles (1,090 km) downstream.^[22] It is joined by the Minnesota River at Fort Snelling, by the St. Croix River near Hastings, by the Chippewa River at Wabasha, and by many smaller streams. The Red River, in the bed of glacial Lake Agassiz, drains the northwest part of the state northward toward Canada's Hudson Bay. Approximately 10.6 million acres (4,300,000 ha; 43,000 km²) of wetlands are contained within Minnesota's borders, the most of any state except Alaska.^[23]