 The fur trade was in decline by the late 1830s . The American Fur Company went bankrupt in 1842 , though the Missouri Fur Company and other operations kept the trade from collapsing entirely . As this trade declined the lumber industry began to grow substantially in areas such as the Saint Croix Valley where valuable white pine was plentiful . New saw mills appeared in Marine and Stillwater . Lumber was typically cut during winter and sent downstream in the spring . In 1848 , businessman Franklin Steele built the first private sawmill on the Saint Anthony Falls ( which would later become the town of Saint Anthony ) opening commercial lumbering on the Mississippi River . More sawmills quickly followed . Soon the Saint Croix and Mississippi Rivers in Minnesota had become major <unk> for lumber headed for Saint Louis and other destinations . 
