History in Depth

Minnesota preserves an extensive geological record, with rocks as old as 3.6 billion years exposed by the last ice age and bedrock soils formed during the early Paleozoic era between 540 and 440 million years ago, when a shallow sea covered this area and created sandstone from an ancient beach, limestone from the sea and its creatures, and shale from mud. Beginning more than 110,000 years ago and lasting until 12,000 years ago, glaciers covered much of North America, formed the Great Lakes, shaped Minnesota’s modern landscape, and left more than 200 feet of drift soils in this part of the state when they receded. Deep below Minnesota’s lakes and rivers, buried sandstone, limestone, and dolomite aquifers in much of the southern half of the state hold valuable groundwater that is cleaner than surface water because it is slowly filtered through rock. Several aquifers lie below this site, including the Prairie du Chien limestone, Jordan sandstone, and Franconia sandstone aquifers. The Gladstone Shops’ well passed through and connected three different aquifers, breaking a confining dolomite layer, and after the well was abandoned it became a potential pathway for surface contaminants to enter the aquifer and threaten drinking water until it was sealed to help protect the groundwater.

Maplewood, Minnesota · United States