McCarthy Beach State Park

ORIGIN OF McCARTHY BEACH

The beautiful, sandy beaches of Sturgeon Lake are a gift from the glaciers.  During the Ice Age of the last two million years, glacial ice advanced out of the Ontario region and repeatedly covered this area.  As the ice advanced, it gouged the earth, scraped up and crushed the rock and soil, and carried these sediments along.  About 12,000 years ago, when the last glacier in this area was receding to the northeast, it left piles of sediment along its edge, forming a ridge of hills called a moraine.  These hills can be seen northeast of Sturgeon Lake, where the ridge they form has a northwest-to-southeast orientation.

The receding glacier also left some stranded blocks of ice in this area.  Glacial meltwater that flowed down onto the lowlands on this side of the moraine was free to meander.  Its slower velocity could not continue to carry the sand it washed out of the ice, so the sand was deposited.  Over time, the sand accumulated creating a large outwash plain that buried the stranded blocks of ice.  Slowly, the hidden ice blocks melted, forming a group of sandy, water-filled basins called kettle lakes.

Since the shores of the kettle lakes and the nearby land were composed entirely of sand, the shorelines eroded readily and the kettles grew until they joined to form Sturgeon Lake with its many bays.  The lake has many wide, shallow margins because waves wash the beach sand into the lake, and as a result, the shoreline migrates outward, widening the shallows.  Under the right conditions, one can see the wide zone of shallow water extending about 100 meters out from the shore near this marker.  The place where the bottom drops off sharply, to a depth of more than two meters, is close to where the shoreline was when it started to migrate.

Erected by the Geological Society of Minnesota in partnership with the Minnesota Department of Transportation, the Minnesota Geological Survey, and the Minnesota Department of Natural Resources   2003