The 1,462 square miles of land surface in the Cannon River watershed varies considerably from areas of low hills and plains to areas dominated by streams deeply incised into bedrock. Much of the south-central part of the area consists of a till plain that ranges in altitude from 1,100 to 1,200 feet above mean sea level. This plain is bordered by end moraines that form ridges on the east, west, and south. The eastern moraine marks the maximum eastward extend of the Wisconsin glacier, rising to more than 1,300 feet above sea level and forming ridges 50 to 100 feet above the till plain. In the northwest, the end moraine ridges are less obvious but extend directly north across the Cannon River valley.
The end moraine ridges were cut by glacial melt water, which also deepened the pre-existing Cannon River valley. This deeply incised valley captures some of the streams that flow westward off the end moraines.
East of the end moraines, pre-Wisconsin age glacial deposits are relatively thin and deeply weathered and eroded.
Lard glacial melt-water valleys, around Cannon Falls and extending several miles to the west and south west, are characterized by broad valley floors underlain by outwash sand and gravel. The Cannon River flows out of the watershed and enters the Mississippi River at about 660 feet altitude.
