The Cedar River Watershed Unit (as established by the states of Minnesota) consists of 1,204 square miles (3,118 square kilometres) of flat or gently undulating plain.
The watershed is drained by the Cedar River and several smaller streams that flow south into Iowa and eventually into the Mississippi River.
Its easternmost neck is part of a broad, flat, well-drained plain, covered by a thin sheet of glacial drift. Sinkholes have formed in the near surface carbonate bedrock, and a karst topography is developing. Farther north, along the east boundary, the drift is more than 200 feet (61 m) thick, and the land surface reaches altitudes of more than 1,450 feet (442 m) – the highest area in southeastern Minnesota. In the central part of the watershed in the southern flood plain of the Cedar River, the drift is less than 100 feet (30 m) thick, and the land surface altitude is less than 1,140 feet (347 m). The western part is dominated by a terminal moraine of the last Wisconsin glacier. Here the drift is more than 300 feet (91 m) thick, is poorly drained, and has numerous lakes.
The watershed is mostly prairie and is well suited for farming, which is the dominant economic activity.
Topographic quadrangle maps published by the U.S. Geological Survey are available for the entire watershed.
