Question: Where does the river on which the United States' largest reservoir is located originate?

full_context: Document 1: Lake Mead: 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.
Document 2: Lake Mohave: Lake Mohave is a reservoir on the Colorado River between the Hoover Dam and Davis Dam in Cottonwood Valley defining the border between Nevada and Arizona in the United States. This 67 mile stretch of the Colorado River flows past Boulder City, Nelson, Searchlight, Cottonwood Cove, Cal-Nev-Ari, and Laughlin to the west in Nevada and Willow Beach and Bullhead City to the east in Arizona. A maximum width of 4 miles wide and an elevation of 647 ft , Lake Mohave encompasses 28,260 acres of water. As Lake Mead lies to the north of the Hoover Dam, Lake Mohave and adjacent lands forming its shoreline are part of the Lake Mead National Recreation Area administered by the U.S. National Park Service.
Document 3: Colorado River (Texas): The Colorado River is an 862 mi long river in the U.S. state of Texas. It is the 18th longest river in the United States and the longest river with both its source and its mouth within Texas.
Document 4: Mississippi River: The Mississippi River is the chief river of the second-largest drainage system on the North American continent, second only to the Hudson Bay drainage system. Flowing entirely in the United States (although its drainage basin reaches into Canada), it rises in northern Minnesota and meanders slowly southwards for 2320 mi to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains all or parts of 31 U.S. states and 2 Canadian provinces between the Rocky and Appalachian Mountains. The Mississippi ranks as the fourth-longest and fifteenth-largest river in the world by discharge. The river either borders or passes through the states of Minnesota, Wisconsin, Iowa, Illinois, Missouri, Kentucky, Tennessee, Arkansas, Mississippi, and Louisiana.
Document 5: Lake Mead National Recreation Area: Lake Mead National Recreation Area is a U.S. National Recreation Area located in southeastern Nevada and northwestern Arizona. Operated by the National Park Service, Lake Mead NRA follows the Colorado River corridor from the westernmost boundary of Grand Canyon National Park to just north of the cities of Laughlin, Nevada and Bullhead City, Arizona. It includes all of the eponymous Lake Mead as well as the smaller Lake Mohave – reservoirs on the river created by Hoover Dam and Davis Dam, respectively – and the surrounding desert terrain and wilderness.
Document 6: Bill Williams River: The Bill Williams River is a 46.3 mi river in west-central Arizona where it, along with its tributary, the Santa Maria River, form the boundary between Mohave County to the north and La Paz County to the south. It is a major drainage westwards into the Colorado River of the Lower Colorado River Valley south of Hoover Dam and Lake Mead, and the drainage basin covers portions of northwest, and west-central Arizona. The equivalent drainage system paralleling the east–west lower reaches of the Bill Williams is the Gila River, which flows east-to-west across central Arizona, joining the Colorado River in the southwest at Yuma. The confluence of the Bill Williams River with the Colorado is north of Parker, and south of Lake Havasu City.
Document 7: Rio Grande: The Rio Grande ( or ; Spanish: Río Bravo del Norte , ] or simply Río Bravo) is one of the principal rivers in the southwest United States and northern Mexico (the other being the Colorado River). The Rio Grande begins in south-central Colorado in the United States and flows to the Gulf of Mexico. Along the way, it forms part of the Mexico–United States border. According to the International Boundary and Water Commission, its total length was 1896 mi in the late 1980s, though course shifts occasionally result in length changes. Depending on how it is measured, the Rio Grande is either the fourth- or fifth-longest river system in North America.
Document 8: Colorado drainage basins: The U.S State of Colorado includes the headwaters of several important rivers. The state is divided into two major hydrographic regions by the Continental Divide of the Americas. East of the Continental Divide, surface waters flow via the South Platte River, the North Platte River, the Republican River, the Arkansas River, the Cimarron River, the Canadian River, or the Rio Grande to the Gulf of Mexico. West of the Continental Divide, surface waters flow via the Green River, the upper Colorado River (formerly the Grand River), or the San Juan River into the Colorado River and on to the Gulf of California. Colorado also has three significant endorheic basins: the San Luis Closed Basin in the San Luis Valley, and the Bear Creek Basin and the White Woman Basin spanning the Colorado-Kansas border north and south of the Arkansas River.
Document 9: Kingman Wash, Lake Mead: Kingman Wash is on the Arizona side of Lake Mead near the Hoover Dam. Lake Mead, and all of its points of interest, is managed by the National Park Service and available to the public for recreational purposes.
Document 10: Colorado River: 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.
Document 11: South Platte River: The South Platte River is one of the two principal tributaries of the Platte River. Flowing through the U.S. states of Colorado and Nebraska, it is itself a major river of the American Midwest and the American Southwest/Mountain West. Its drainage basin includes much of the eastern flank of the Rocky Mountains in Colorado; much of the populated region known as the Colorado Front Range and Eastern Plains; and a portion of southeastern Wyoming in the vicinity of the city of Cheyenne. It joins the North Platte River in western Nebraska to form the Platte, which then flows across Nebraska to the Missouri. The river serves as the principal source of water for eastern Colorado. In its valley along the foothills in Colorado, it has permitted agriculture in an area of the Colorado Piedmont and Great Plains that is otherwise arid.
Document 12: San Juan River (Colorado River): The San Juan River is a major tributary of the Colorado River in the southwestern United States, providing the chief drainage for the Four Corners region of Colorado, New Mexico, Utah and Arizona. Originating as snowmelt in the San Juan Mountains (part of the Rocky Mountains) of Colorado, it flows 383 mi through the deserts of northern New Mexico and southeastern Utah to join the Colorado River at Glen Canyon. The river drains a high, arid region of the Colorado Plateau and along its length it is often the only significant source of fresh water for many miles. The San Juan is also one of the muddiest rivers in North America, carrying an average of 25 million US tons (22.6 million t) of silt and sediment each year.
Document 13: Colorado River Aqueduct: The Colorado River Aqueduct, or CRA, is a 242 mi water conveyance in Southern California in the United States, operated by the Metropolitan Water District of Southern California (MWD). The aqueduct impounds water from the Colorado River at Lake Havasu on the California-Arizona border west across the Mojave and Colorado deserts to the east side of the Santa Ana Mountains. It is one of the primary sources of drinking water for Southern California.
Document 14: Hoover Dam: Hoover Dam, originally known as Boulder Dam from 1933 to 1947, when it was officially renamed Hoover Dam by a joint resolution of Congress, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President Franklin D. Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives. The dam was named after President Herbert Hoover.
Document 15: Theodore Roosevelt Lake: Theodore Roosevelt Lake (usually called Roosevelt Lake, sometimes Lake Roosevelt) is a large reservoir formed by Theodore Roosevelt Dam on the Salt River in Arizona as part of the Salt River Project (SRP). Located roughly 80 miles (130 km) northeast of Phoenix in the Salt River Valley, Theodore Roosevelt is the largest lake or reservoir located entirely within the state of Arizona (Lake Mead and Lake Powell are larger but both are located partially within the neighboring states of Nevada and Utah respectively). Both the reservoir and the masonry dam that created it, Roosevelt Dam, were named for U.S. President Theodore Roosevelt who dedicated the dam himself in March 1911. Roosevelt Lake is a popular recreation destination within the Tonto National Forest, as such the facilities located at this lake are managed by that authority.
ground_truth: the central Rocky Mountains