[map of Brainerd Lakes region]
Geology of Minnesota
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. Water flowing from the surface of the receding ice deposited sand and gravel around and over these severed parts of the glacier and formed an outwash plain studded with huge blocks of partly buried, motionless ice.
On melting, the detached blocks - some of which were miles in extent and scores of feet thick - left permanent, water-filled depressions in the gravel plain. The lakes so formed, including those portrayed on this tablet, do not follow the original shape of the ice blocks but are commonly round or elliptical due to subsequent shore line changes.
ERECTED BY THE GEOLOGICAL SOCIETY OF MINNESOTA
AND THE DEPARTMENT OF HIGHWAYS, STATE OF MINNESOTA
AIDED BY A GRANT FROM THE
LOUIS W. AND MAUD HILL FAMILY FOUNDATION