About the Cannon River Watershed

What exactly is a “watershed?” A watershed is an area of upslope land that drains to a specific channel or waterway. All of the land in the Cannon River watershed drains to the Cannon River or to one of its tributaries. Take a look at the example below; Turtle Creek south of Owatonna drains to the Straight River. The Straight River drains to the Cannon River. Turtle Creek and the Straight River are both in the Cannon River’s watershed. The Cannon River, in turn, drains to the Mississippi River and is within the Mississippi Basin (think of a basin as a really big watershed).

Beneath the Cannon River watershed lies sedimentary rocks; sandstone, limestone, and dolostone. The deepest of these rocks overlay older sedimentary rocks formed during the Proterozoic era, 1,200 to 900 million years ago. A series of sandstone and sandy limestone formations lay above this, including the Mt. Simon Sandstone and the Jordan Sandstone. These sandstones are overlain by Prairie du Chien Group dolostone formations, the St. Peter Sandstone, and the Dechora Shale.

In the western and southern portion of the watershed, these rocks have been buried beneath 100 to 200 feet of glacial drift. During the most recent glacial period, the Wisconsin Glaciation, glacial melt water deposited a thick layer of glacial drift, a mixture of sand, gravel, and rocks. As the glaciers receded north, drainage water carved out well-developed stream and river channels into the drift and created lakes in the western portion of the watershed.

Travel east towards the Mississippi, this glacial drift thins and is virtually non-existent when you enter Goodhue County. This area, where there is little or no glacial drift, is called the “driftless zone.” In this part of the watershed, and throughout much of southeast Minnesota, the previous glaciation which shaped the southern and western portions of the watershed, did not reach this area. Consequently, the limestone and sandstone bedrock were never buried under glacial till. Exposed to thousands of years glacial melt water and drainage, the bedrock has eroded away and created a more hilly terrain and formed the magnificent bluffs of the Mississippi River valley.

The groundwater in the region is stored in the sedimentary rock formations mentioned above in bedrock “aquifers.” An aquifer is a layer of rock that holds water in pore spaces wtihin the rock. From the surface, a well can be drilled into one of these aquifers and useable water can be drawn. The most heavily used aquifer throughout the watershed is the St. Peter-Prairie du Chein-Jordan aquifer, while other deeper aquifers such as the Franconia-Ironton-Galesville or Mt. Simon-Hinckley aquifers are not as widely tapped. Older wells in the western portion of the watershed have also used groundwater stored in glacial drift, however these sources are not very reliable and are slow to recharge.

On the surface, the topography of the watershed varies. The southern and western portion are largely flat while the eastern portion of the watershed is hilly. Although currently dominated by agricultural land use, historically, the southern portion of the watershed was prairie or oak savannah. According to information from pre-settlement surveys, grasses as tall as eight feet once grew there, with frequent wildfires sweeping across the prairie keeping trees and other plant life to a minimum.

The western and central portion of the watershed was in “Big Woods.” The Big Woods was an expanse of hardwood forest that extended from central Minnesota into south-central and southeastern portions of the state. A thick forest of elm, maple, basswood, and red oak dominated the terrain, broken up only by lakes and small wetlands.

The eastern portion of the watershed consists primarily of oak savannah and prairie, much like the southern portion of the watershed. However, the area is populated by species that can grow successfully on the hilly and rocky terrain. Likewise, as you descend into the Mississippi River valley, floodplain forest populated by maples and cottonwoods become prevalent in addition Big Woods remnants.

Today, much of the land in the Cannon River watershed has been converted for agricultural use. Windblown sediment called loess that coated the region after the glaciers had receded contributes to the fertility of the region. That, combined with nutrient rich prairie soils, provide valuable land for corn, soybean, and other crop production.

The two main rivers in the Cannon River watershed are the Cannon and Straight Rivers. The Cannon River originates in Shields Lake and flows west before turning south. The river turns again east as it goes through Waterville, MN and continues on to Faribault, MN where the Straight River drains into it. The Straight River begins in Oak Glen Lake south of Owatonna, MN. It flows directly north before it dumps into the Cannon River. From Faribault, the Cannon flows north through Northfield, MN and finally turns west. As it travels through the Byllesby Resevoir and Cannon Falls, MN, the Cannon finally drains to the Mississippi River just north of Red Wing, MN.

From the highest point of the Straight River to the confluence of the Mississippi and the Cannon, the river drops over 500 feet in altitude. The Cannon flows nearly 130 miles from Shields Lake to the Mississippi, while the Straight River flows approximately 65 miles north to its confluence with the Cannon. Add over 630 miles of smaller perennial streams flowing into the Cannon and Straight, and water courses in the Cannon River watershed cover over 800 linear miles, draining a watershed area of 1,470 square miles! That’s nearly the size of the state of Rhode Island!