North Shore Highlands

The North Shore Highlands are a physiographic and ecological region of the U.S. state of Minnesota in central North America. They were formed by a variety of geologic processes, but are principally composed of rock created by magma and lava from a rift about 1.1 billion years ago, which rock formations are interspersed with and overlain by glacial deposits. Their ecology derives from these origins, with thin, rocky soils supporting flora and fauna typical of their northern, inland location.

The North Shore Highlands are part of what once was called the Cabotian Mountains, a name applied to the highlands north of Lake Superior. They are bounded on the south by the North Shore of Lake Superior, from which they rise in rock formations ranging from gentle slopes to sheer cliffs. They extend from the Dalles of the Saint Louis River in Jay Cooke State Park on the west near Thomson, Minnesota, to the Grand Portage Highlands in the Grand Portage Indian Reservation at the easternmost extremity of the state. Between these anchors are cliffs along the shore such as Silver Creek Cliff, Split Rock, Palisade Head, and Shovel Point; the Sawtooth Range, also lakeside in the central part of the uplands; and the inland Misquah Hills to the east, containing Eagle Mountain, the highest point in Minnesota.

Geologically, the region is part of the southern reaches of the rugged Canadian Shield, the core of the North American craton. The bedrock was created during the Midcontinent Rift, a failed rift which occurred some 1.1 billion years ago. As the continent sundered, magma and lava flowed upward, which cooled into the present-day rock of the Duluth Complex and North Shore Volcanic Group. Much of these rocks remain exposed, often in prominences which were more resistant to erosion. Mafic intrusions of gabbro of the Duluth Complex anchor both ends of the highlands, to the west of Duluth and above Grand Portage Bay to the east. Between them is an area of basaltic rocks of the North Shore Volcanics, interspersed with occasional mafic rocks. These basaltic layers, formed from lava emitted from rift fissures in the center of what is now Lake Superior, subsided in the middle (forming the present lake basin); the edges angle upward from the lake in a serrated series of ridges known as the Sawtooth Mountains along the lakeshore.

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