Savanna Portage State Park - Geology and Topography

Geology and Topography

The park is located on the divide between the watersheds of the Great Lakes and the Gulf of Mexico, both of which drain to the Atlantic Ocean. The area is a low-relief plain which was once a glacial lakebed. During the last phase of the Wisconsinan glaciation, the deteriorating continental glacier left behind connected lakes, known as Glacial Lakes Aitkin and Upham. Formed by the retreat of the St. Louis Sublobe of the Superior Lobe of the glacier, Lake Upham drained through Lake Aitkin to the Mississippi River. The retreating glacier and the lakes deposited sand and sediments in the lakebed. As the lakes drained these sediments became the present plain.

The plain at first was drained by the Cloquet River, which then ran west to the Mississippi. By the process of stream piracy, the smaller Saint Louis River, which runs to Lake Superior, captured the Cloquet and most of its drainage basin. This left behind the East Savanna River which drains into the St. Louis, Lake Superior, the lower Great Lakes, and the Saint Lawrence River, and to the west, the West Savanna River, which is tributary to the Mississippi.

The old lake plain is part of the Tamarack Lowlands Subsection within the Northern Minnesota Drift Plains Section of the Laurentian Mixed Forest. Lacustrine sediments deposited by the glacial lake are parent to the present soils of peats, silt, and sand; the peats are in marshes which form large parts of the park. These wet lowlands adjoin rolling hills which are end moraines of the recent glaciation. These moraines are part of the St. Louis Moraines Subdivision of the Northern Minnesota Drift Plain.