Question: Where does the river on which the United States' largest reservoir is located originate?
Context: Kerr Lake /kɑr/ (officially John H. Kerr Reservoir, also known as Bugg's Island Lake) is a reservoir along the border of the U.S. states of North Carolina and Virginia.  It is impounded by the John H. Kerr Dam, constructed between 1947 and 1952 to produce electricity and to provide flood control.  Kerr Lake is owned by the US Army Corps of Engineers, and is the largest reservoir in Virginia.  It is located in parts of Vance, Granville, and Warren counties in North Carolina, and Mecklenburg, Charlotte, and Halifax counties in Virginia.  At its maximum capacity, it is one of the largest reservoirs in the Southeastern United States, covering approximately 50000 acre and bordered by over 850 mi of shoreline.  The lake is named for Congressman John H. Kerr of North Carolina, who supported the original creation of the lake. Elephant Butte Reservoir is a reservoir on the Rio Grande in the U.S. state of New Mexico, 5 mi north of Truth or Consequences.  This reservoir is the 84th largest man-made lake in the United States and the largest in New Mexico by total surface area.  It is the only place in New Mexico where one can find pelicans perched on or alongside the lake.  There are also temporary US Coast Guard bases stationed at Elephant Butte.  It is impounded by Elephant Butte Dam and is the largest reservoir in New Mexico by peak volume.  The reservoir is also part of the largest state park in New Mexico, Elephant Butte Lake State Park. Lake Mead is the largest reservoir in the United States in terms of water capacity.  Formed by the Hoover Dam, the reservoir serves water to the states of Arizona, California, and Nevada, providing sustenance to nearly 20 million people and large areas of farmland.  Lake Mead is on the Colorado River, about 24 mi from the Las Vegas Strip, southeast of the city of Las Vegas, Nevada, in the states of Nevada and Arizona. Shasta Dam (called Kennett Dam before its construction) is a concrete arch-gravity dam across the Sacramento River in Northern California in the United States.  At 602 ft high, it is the eighth-tallest dam in the United States.  Located at the north end of the Sacramento Valley, Shasta Dam creates Shasta Lake for long-term water storage, flood control, hydroelectricity and protection against the intrusion of saline water.  The largest reservoir in the state, Shasta Lake can hold about 4500000 acre-ft . Elephant Butte Lake State Park is a state park of New Mexico, United States, located 7 mi north of Truth or Consequences along the shore of Elephant Butte Reservoir.  It is the largest state park in New Mexico and surrounds the state's largest reservoir.  The 36000 acre reservoir, created in 1916 across the Rio Grande, is 40 mi long with more than 200 mi of shoreline. Ah Pah Dam was a proposed dam on the Klamath River in the U.S. state of California proposed by the United States Bureau of Reclamation as part of its United Western Investigation study in 1951.  It was to have been 813 ft high and was to be located 12 mi upstream of the river's mouth.  It would stand almost as tall as the Transamerica Pyramid building in San Francisco, but would be much more massive.  It would flood 40 mi of the Trinity River, including the Yurok, Karuk and Hupa Indian Reservations, the lower Salmon River, and 70 mi of the Klamath River, creating a reservoir with a volume of 15000000 acre.ft – two-thirds of the size of Lake Mead, and becoming the largest reservoir in California.  The water would flow by gravity through a tunnel 60 mi long to the Sacramento River just above Redding and onward to Southern California, in an extreme diversion plan known as the Klamath Diversion.  The tunnel would have been located near the southernmost extent of the reservoir.  It was named in the language of the Yurok people. The San Luis Reservoir is an artificial lake on San Luis Creek in the eastern slopes of the Diablo Range of Merced County, California, approximately 12 mi west of Los Banos on State Route 152, which crosses Pacheco Pass and runs along its north shore.  It is the fifth largest reservoir in California.  The reservoir stores water taken from the San Joaquin-Sacramento River Delta.  Water is pumped uphill into the reservoir from the O'Neill Forebay which is fed by the California Aqueduct and is released back into the forebay to continue downstream along the aqueduct as needed for farm irrigation and other uses.  Depending on water levels, the reservoir is approximately nine miles long from north to south at its longest point, and five miles (8 km) wide.  At the eastern end of the reservoir is the San Luis Dam, or the B.F. Sisk Dam, the fourth largest embankment dam in the United States, which allows for a total capacity of 2041000 acre.ft . Caballo Lake is a reservoir on the Rio Grande in southern New Mexico, United States.  It is the fourth largest reservoir in New Mexico in terms of surface area and the fifth largest body of water in New Mexico in terms of volume.  The lake is in Caballo Lake State Park, which is approximately 16 mi south of Truth or Consequences. This is a list of the largest reservoirs in the state of Colorado.  All thirty-eight reservoirs that contain greater than 40,000 acre-feet (.0493 km) are included in the list.  Most of the larger reservoirs in the state are owned by the United States Bureau of Reclamation and, to a lesser extent, the Corps of Engineers.  Additionally, a number of these reservoirs are owned by private companies for flood control and irrigation purposes.  The largest reservoir entirely contained in Colorado is Blue Mesa Reservoir, with a capacity of 829,500 acre-feet (1.2032 km).  The total storage of the reservoirs on this list is 3,763,458 acre-feet (4.642 km), although not all is allocated for use by Colorado. The Colorado River is one of the principal rivers of the Southwestern United States and northern Mexico (the other being the Rio Grande).  The 1450 mi river drains an expansive, arid watershed that encompasses parts of seven U.S. and two Mexican states.  Starting in the central Rocky Mountains in the U.S., the river flows generally southwest across the Colorado Plateau and through the Grand Canyon before reaching Lake Mead on the Arizona–Nevada border, where it turns south toward the international border.  After entering Mexico, the Colorado approaches the mostly dry Colorado River Delta at the tip of the Gulf of California between Baja California and Sonora.
Answer: the central Rocky Mountains