The Gunnison River is a tributary of the Colorado River rising on the Western Slope of the Rocky Mountains in southwestern Colorado. The Aspinall Unit above and in the Black Canyon of the Gunnison prior to 2009 was managed to maximize power generation and water storage. In May, 2009, due to successful pursuit of federal water rights by the National Park Service, 16 billion gallons of water were released and flowed through the Black Canyon scouring the bed of the river in a manner mimicing natural spring runoff flushing the river bed. Flow peaked at 7,300 cubic feet per second (cfs) on May 13, 2009.