Written by Al Agnew- Because of geology, the St. Francis is far from a typical Ozark stream. It is the master stream of the St. Francois Mountain area (note the different spelling), which is the geologic center of the Ozark uplift. The volcanic rock knobs, peaks, and canyons of the St. Francois Mountains are the oldest exposed rock in the central United States. Often generically called granite, though relatively little of the rock is true granite, it is generally harder and more resistant to weathering and erosion than the dolomitic limestones and sandstone that surround it and once covered much if not all of it. So not only do the “mountains” now survive where the overlying sediments have been removed, the river valleys, where they encounter this resistant rock, have formed V-shaped, boulder-strewn canyons called shut-ins.