Geology of Minnesota

Geology of Minnesota. Lake Harriet Region. , 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 hills were formed as conditions changed. The Lake Harriet landscape has such an origin. , Leaving the present channel of the Mississippi River at the Plymouth Avenue Bridge, a preglacial valley runs almost directly south beneath Lake of the Isles, Lake Calhoun and Lake Harriet to the Minnesota River at Bloomington. This valley was mostly filled but not completely obliterated by glacial deposits. The unfilled portions of the valley are now basins, which are filled by lakes perched high on the glacial debris. Lake Harriet lies directly over this ancient valley. Its surface 250 feet above the valleys rocky floor and is in a setting of hills piled up while the ice front paused here in its final retreat about 10,000 years ago. , , Erected by the Geological Society of Minnesota , and the Board of Park Commissioners, City of Minneapolis , Aided by a Grant from the , Louis W. and Maud Hill Family Foundation , 1955.