What does the future of the Gordon Flowage have to do with its geography?

At the conclusion of his book, Brule Country, Albert M. Marshall discusses the future of the Brule River Valley in a way that seems directly relevant to the future of the upper St. Croix River.

In some respects the Brule Valley -- because of the character of the land surrounding it -- has been its [the Brule River's] protector.  The sandy barrens which stretch along its eastern border are today almost as they were when Du Lhut ventured by.  Men who have studied the reports of the original surveyors who ran the township lines back in the 1850's find that the cover is practically identical with that which they describe -- clumps of jack pines with an occasional sentinel white or Norway pine overlooking the undulating plains with their meager vegetation.  As long as this sandy barren remains to filter the rains which feed the springs along the Brule's banks, the river cannot dry up.  And it is reasonable to suppose that the very infertility of this border land will discourage cultivation and settlement.  Whether the Valley can be protected from the seeds of destruction blowing from some other quarters cannot yet be answered.  Probably as long as fishing remains the chief consideration, there will be no overt attempt to sell the Brule's riches to the pawnbrokers.  Many hope that no human hand will be allowed to molest the mighty pines, which in their younger days gazed down on the occasional fur trader ferrying his bulky packets along the swiftly moving currents.  Nor that the call of the whippoorwill of a summer's night will be rudely interrupted by man-made noises.  They want this little corner of the North American continent to remain close to its natural state so as to  remind people of another day and age and of the treasures and the heritage that Mother Nature has bequeathed to them!