Upper Black Rocks area has a class 2 rapid. The river makes a sharp left entering a mile long zone of narrow, turbulent water.  Take it down the left at the top.  At high water, watch for weird turbulence and strong eddie lines, suck holes and boils.  This area can give unwary boaters trouble, especially in open canoes.  BEWARE OF JUMPING OR DIVING OFF ROCKS as people have been trapped and killed by hidden rocks and suck holes.  Here the Colorado River cuts through the Uncompahgre Plateau's basement rock, the same 1.5 billion year old uplifted metamorphic rock that is seen in the Black Canyon of the Gunnison, in Unaweep Canyon southwest of Grand Junction and at the base of the Colorado National Monument.  Geologists call it schist and gneiss, and this same formation creates the rapids of Westwater Canyon.  At this point the river is a suprisingly 85 FEET DEEP!!!! The fast moving, turbulent water is perfect habitat for the endangered Humpback Chub which uses its hump and large wing like fins as hydroplanes in the swift currents.  Chub are knwon to travel between Westwater and Black Rocks, possibly using riffles and eddies as spawning habitat.