Friday 18 July 2014
The Boundary Waters Canoe Area Wilderness, is a 1,090,000-acre wilderness area within the Superior National Forest in northeastern Minnesota (USA) under the administration of the U.S. Forest Service. The BWCAW is renowned as a destination for both canoeing and fishing on its many lakes and is the most visited wilderness in the United States. The lakes of the BWCAW are located in depressions formed by differential erosion of the tilted layers of the Canadian Shield. For the past two million years, massive sheets of ice have repeatedly scoured the landscape; the last glacial period ended with the retreat of the Laurentide Ice Sheet from the Boundary Waters about 17,000 years ago. The resulting depressions in the landscape later filled with water, becoming the lakes of today. Many varieties of Precambrian bedrock are exposed, including granite, basalt, greenstone, gneiss, as well as metamorphic rocks derived from volcanic and sedimentary rocks. Greenstone of the Superior craton located near Ely, Minnesota is up to 2.7 billion years old, some of the oldest exposed rock in the United States. Source
