The lower St. Croix River watershed is an elongate area of about 930 square miles bounded on the east by the St. Croix River.
The St. Croix River forms the Minnesota-Wisconsin boundary along the eastern side of the watershed. Additional drainage to the St. Croix River includes areas of about 2,500 square miles upstream in Minnesota and about 4,340 square miles in Wisconsin. At the southern tip of the watershed, the St. Croix joins the Mississippi River.
Because part of the St. Croix River is deeply entrenched, topography in the watershed ranges from relatively rugged in highly dissected areas near the river to nearly flat in the west-central area.
In the southern third of the watershed and along the St. Croix River, many outcrops of Ordovician, Cambrian, and Precambrian bedrock occur. The remainder of the watershed is covered by glacial deposits whose maximum thickness is about 400 feet.
Much of the original forest cover, primarily hardwoods, has been removed; the largest concentrations remaining are long the St. Croix River and in the west-central area.
The proximity of the watershed to the expanding Minneapolis-St. Paul metropolitan area emphasizes the importance of defining water resources essential for future growth.
