Physiography, Relief, and Drainage

Inspiration Peak, the highest elevation in Otter Tail County, is approximately 1,750 feet above sea level. It is on the Alexandria Moraine Complex in the southeastern part of the county, west of Urbank. The lowest point in the county is at an elevation of approximately 1,010 feet above sea level where the Otter Tail River exits the southwest corner of the county.

The county can be divided into five broadly defined landform regions. These are the stagnation moraines, till plains, Wadena Drumlin Field, pitted outwash plains, and Glacial Lake Agassiz Lake Plain. The areas of stagnation moraine are comprised of geomorphic regions of the Alexandria Moraine Complex and Big Stone Moraine Complex, which make up about 35 percent of the county. The topography of the stagnation moraine associated with the Alexandria Moraine Complex has high relief with differences in elevation ranging from 10 to 120 feet. The area is gently undulating to steep and is characterized by wet depressions, marshes, and numerous small to large lakes. The stagnation moraine associated with the Big Stone Moraine Complex has undulating to hilly topography with lower relief. The differences in elevation commonly range from 10 to 50 feet. This moraine has wet depressions, marshes, and a few small lakes. Attempts have been made to drain the wet depressions within the moraines, but the complex landscape and a lack of drainage outlets have hindered these practices.

In the northeastern part of the county is the Wadena Drumlin Field, which makes up about 6 percent of the county. The topography is dominated by gently sloping to strongly sloping landscapes of moderate relief. The local relief generally ranges from a few feet to about 30 feet. Many of the depressions between the drumlins are commonly drained by shallow drainageways or deeper drainage ditches. The ditches and drainageways remove the excess surface water.

The Henning and Fergus Falls till plains make up 18 percent of the county. The topography is dominated by nearly level to hilly landscapes with short slopes. These areas have moderate relief with differences in elevation commonly ranging from 5 to 50 feet.

The Detroit Lakes Pitted Outwash Plain in the central part of the county and along the meltwater channel of the Pelican River and the Park Rapids- Staples Outwash Plain in the southeast corner of the county make up 40 percent of the county. The topography of the outwash plain areas is nearly level to hilly and has low or moderate relief. The differences in elevation typically range from a few feet to about 40 feet. The Detroit Lakes Pitted Outwash Plain commonly has small to large lakes and small wet depressions.

The Park Rapids-Staples Outwash Plain has less relief. It has fewer lakes than other areas but contains more and larger wet depressions, which result from the shallower surficial ground-water table. Many of the large depressions have been drained by ditches that outlet into tributaries of the Leaf River or the Wing River.

The Glacial Lake Agassiz Lake Plain in the southwest corner of the county makes up approximately 1 percent of the county. The area typically is flat or nearly level but ranges to gently sloping in the vicinities of the glacial beach ridges. This area contains a few drainage ditches, and almost all of the soils have some form of surface drainage. The area also has some small and medium depressions.

The continental divide that separates north-flowing waters from south-flowing waters lies in an irregular line near Butler to New York Mills, then south towards Urbank, northwest towards Underwood, and finally south to just west of Dalton. North-flowing waters drain via the Red River into the Hudson Bay, and southflowing waters drain via the Crow Wing and Minnesota Rivers into the Mississippi River.