Book excerpt: Growing up in the river town of Morton, Darby Nelson developed a deep taproot of affection that anchored his contagious curiosity about the land and people of the Minnesota River Valley. Now, with an ecologist's lens and a lifelong appreciation for wild and scenic places, Darby sets out with his wife, Geri, to paddle the river all the way from its source near the Minnesota-South Dakota border to its confluence with the Mississippi in the Twin Cities.