 Joseph Nicollet scouted the area in the late 1830s , exploring and mapping the Upper Mississippi River basin , the St. Croix River , and the land between the Mississippi and Missouri Rivers . He and John C. Frémont left their mark in the southwest of the state , carving their names in the pipestone quarries near Winnewissa Falls ( an area now part of Pipestone National Monument in Pipestone County ) . 
