Colorado River
Major river of the southwestern U.S. and northern Mexico.
Agnieszka Kwiecień, Nova · CC BY-SA 4.0
The Colorado River, also called the Río Colorado in Spanish, is a major river in the Southwestern United States and northern Mexico, alongside the Rio Grande. Stretching 1,450 miles (2,330 km), it ranks as the fifth-longest river in the U.S. and drains a vast, dry watershed covering parts of seven U.S. states and two Mexican states. Its name comes from the Spanish word for "colored reddish," a reference to the heavy silt it once carried. The river begins in Colorado’s Rocky Mountains, then flows generally southwest across the Colorado Plateau and through the Grand Canyon. It reaches Lake Mead at the Arizona–Nevada border, where it turns south toward the international boundary. After crossing into Mexico, it ends at the mostly dry Colorado River Delta, located at the tip of the Gulf of California between Baja California and Sonora. The river is famous for its dramatic canyons, whitewater rapids, and eleven U.S. National Parks. Its waters and tributaries supply a vital source of water for 40 million people. A vast network of dams, reservoirs, and aqueducts diverts nearly all of its flow for farming and city water. The river’s large volume and steep drop generate hydroelectricity, helping meet peak power demands across much of the Intermountain West. Heavy water use has dried up the lower 100 miles (160 km) of the river, which has rarely reached the sea since the 1960s. People have lived in the Colorado River basin for at least 8,000 years. Around 1 CE, large farming societies emerged, but drought and poor land use led to their collapse by the 1300s. Their descendants include tribes like the Puebloans, while others, such as the Navajo, arrived in the basin after the 1000s. Spanish explorers began mapping and claiming the watershed in the 1500s, and it became part of Mexico after its independence from Spain in 1821. Even after most of the watershed became U.S. territory in 1846, much of the river’s course remained unknown. Several mid-19th-century expeditions charted the Colorado; one, led by John Wesley Powell, was the first to run the Grand Canyon’s rapids. Large-scale settlement of the lower basin began in the mid-to-late 1800s, with steamboats sailing from the Gulf of California to river landings linked to wagon roads inland. Gold and silver strikes starting in the 1860s drew prospectors to the upper basin. Large-scale river management started in the early 1900s, guided by a series of international and U.S. interstate treaties known as the "Law of the River." The U.S. federal government built most major dams and aqueducts between 1910 and 1970; the largest, Hoover Dam, was completed in 1935. State and local governments also took part in numerous water projects. With all their waters fully allocated, the Colorado and the neighboring Rio Grande are now among the most controlled and litigated river systems in the world. Since 2000, extended drought has clashed with growing demands for Colorado River water, and the level of human development and control continues to spark controversy. **Course**
The Colorado begins as many tributaries in Wyoming and Colorado, the largest being the Green River. The Colorado River itself starts in Rocky Mountain National Park, then runs briefly south before turning west below Grand Lake, Colorado’s largest natural lake. For its first 250 miles (400 km), it carves through the mountainous Western Slope, a sparsely populated area west of the Continental Divide. Flowing southwest, it gains strength from many small tributaries and larger ones like the Blue, Eagle, and Roaring Fork rivers. After passing through De Beque Canyon, the Colorado leaves the Rockies and enters the Grand Valley, a major farming and ranching region. There, at Grand Junction, it meets one of its largest tributaries, the Gunnison River. Most of the upper river is a swift whitewater stream, 200 to 500 feet (60 to 150 m) wide and 6 to 30 feet (2 to 9 m) deep, with a few exceptions like the Blackrocks reach, where it is nearly 100 feet (30 m) deep. In some areas, such as the marshy Kawuneeche Valley near the headwaters and the Grand Valley, the river shows braided characteristics. From Grand Junction, the Colorado turns northwest, then cuts southwest across the Colorado Plateau, a vast high desert centered at the Four Corners of the southwestern U.S. Here, the climate is much drier than in the Rockies, and the river becomes entrenched in progressively deeper gorges of bare rock, starting with Ruby Canyon and then Westwater Canyon as it enters Utah, now heading southwest again. Farther downstream, it receives the Dolores River and defines the southern border of Arches National Park, before passing Moab and flowing through "The Portal," where it exits the Moab Valley between two 1,000-foot (300 m) sandstone cliffs. In Utah, the Colorado flows mainly through "slickrock" country, known for its narrow canyons and unique folds created by tilted sedimentary rock layers along faults. This is one of the most inaccessible parts of the continental United States. Below its confluence with the Green River, its largest tributary, in Canyonlands National Park, the Colorado enters Cataract Canyon, named for its dangerous rapids, and then Glen Canyon, known for its arches and erosion-sculpted Navajo sandstone formations. Here, the San Juan River, carrying runoff from the southern slope of Colorado’s San Juan Mountains, joins from the east.
- length
- 1,450 miles (2,330 km)
- source
- Rocky Mountains of Colorado
- mouth
- Colorado River Delta at the tip of the Gulf of California
- major_tributaries
- Green River, Gunnison River, Dolores River, San Juan River, Little Colorado Rive
- major_dam
- Hoover Dam (completed 1935)
- largest_reservoir
- Lake Mead
- name_origin
- Spanish for 'colored reddish' due to heavy silt load
Verified Timeline
Lore & Background
Native Americans have inhabited the Colorado River basin for at least 8,000 years. Starting around 1 CE, large agriculture-based societies were established, but a combination of drought and poor land use practices led to their collapse in the 1300s. Their descendants include tribes such as the Puebloans, while others including the Navajo settled in the Colorado Basin after the 1000s. In the 1500s, Spanish explorers began mapping and claiming the watershed, which became part of Mexico upon winning its independence from Spain in 1821. Even after most of the watershed became US territory in 1846, much of the river's course remained unknown. Several expeditions charted the Colorado in the mid-19th century—one of which, led by John Wesley Powell, was the first to run the rapids of the Grand Canyon. Large-scale settlement of the lower basin began in the mid- to late-1800s, with steamboats sailing from the Gulf of California to landings along the river that linked to wagon roads to the interior. Starting in the 1860s, gold and silver strikes drew prospectors to the upper Colorado River basin.
Reader's Guide
The Colorado River and its tributaries are a vital source of water for 40 million people. An extensive system of dams, reservoirs, and aqueducts divert almost its entire flow for agricultural irrigation and urban water supply. Its large flow and steep gradient are used to generate hydroelectricity, meeting peaking power demands in much of the Intermountain West. Intensive water consumption has dried up the lower 100 miles (160 km) of the river, which has rarely reached the sea since the 1960s. Large-scale river management began in the early 1900s, with major guidelines established in a series of international and US interstate treaties known as the "Law of the River". The US federal government constructed most of the major dams and aqueducts between 1910 and 1970; the largest, Hoover Dam, was completed in 1935. With all of their waters fully allocated, both the Colorado and the neighboring Rio Grande are now considered among the most controlled and litigated river systems in the world. Since 2000, extended drought has conflicted with increasing demands for Colorado River water, and the level of human development and control of the river continues to generate controversy.
Did You Know?
- The Colorado River is the 5th longest in the United States, at 1,450 miles (2,330 km).
- Its name comes from the Spanish for "colored reddish" because of its heavy silt load.
- The river has rarely reached the sea since the 1960s due to intensive water consumption.
- Hoover Dam, completed in 1935, is the largest of the major dams built by the US federal government between 1910 and 1970.
- John Wesley Powell led the first expedition to run the rapids of the Grand Canyon in the mid-19th century.
A 1,450-Mile Journey Through the Southwest
The Colorado River traces a 1,450-mile journey from the Rocky Mountains of Colorado to the tip of the Gulf of California, making it the fifth-longest river in the United States. Its name, drawn from the Spanish word for "colored reddish," reflects the heavy silt that gives the water its distinctive hue. The river's path is anything but straightforward: it begins in Rocky Mountain National Park, carves through the mountainous Western Slope of Colorado, then swings across the arid Colorado Plateau, threading through Utah's slickrock country and Arizona's deepest gorges before reaching the Arizona–Nevada border. Along the way it passes through eleven U.S. National Parks, including the Grand Canyon, and drains a watershed spanning seven American states and two Mexican states. The river's character shifts dramatically—from swift whitewater stretches 200 to 500 feet wide in the upper reaches, to the towering sandstone cliffs of "The Portal" near Moab, to the flooded Glen Canyon reach now submerged beneath Lake Powell.
Eight Millennia of Human Presence
Long before European contact, Native Americans had called the Colorado River basin home for at least eight millennia. Around the turn of the first millennium CE, large agricultural societies took root in the basin, but a convergence of prolonged drought and unsustainable land practices brought those communities down by the 1300s. Descendant groups, including the Puebloans, persisted in the region, while the Navajo arrived in the basin after the 1000s. Spanish explorers entered the picture in the 1500s, mapping and claiming the watershed, which passed to Mexico upon its 1821 independence. Even after the United States acquired most of the basin in 1846, much of the river's course remained uncharted. Mid-nineteenth-century expeditions finally brought the waterway into the public imagination—most famously John Wesley Powell's party, the first to navigate the Grand Canyon's rapids. The 1860s gold and silver strikes pulled prospectors into the upper basin, and by the late 1800s steamboats were running from the Gulf of California upriver to landings connected by wagon roads.
The Law of the River and a Web of Dams
The Colorado River is arguably the most heavily engineered waterway in the Western Hemisphere. Beginning in the early 1900s, a framework of international and interstate treaties—collectively called the "Law of the River"—set the rules for allocating its waters among seven U.S. states and two Mexican states. The U.S. federal government then built the vast majority of the major dams and aqueducts between 1910 and 1970, with Hoover Dam, completed in 1935, standing as the largest of these structures. Glen Canyon Dam, finished in the 1960s, flooded the Glen Canyon reach to create Lake Powell. Together, this network diverts nearly the entire flow of the river to serve agricultural irrigation and urban water supply for roughly 40 million people, while the river's steep gradient and volume generate hydroelectricity that meets peaking power demands across the Intermountain West. Because every drop is formally allocated, the Colorado and its neighbor the Rio Grande are now regarded as among the most controlled—and most litigated—river systems on Earth.
When the River Stops Before the Sea
The very success of the Colorado River's management system has come at a profound ecological cost. Intensive upstream consumption has dried up the lower 100 miles of the river, and since the 1960s the water has rarely made it to the sea at the Colorado River Delta, a mostly dry expanse at the tip of the Gulf of California between Baja California and Sonora. The river, once a living connection to the ocean, now often ends in dust. Compounding this, an extended drought that has persisted since 2000 has collided with steadily rising demand from the 40 million people who depend on the basin's water. The tension between human development and the river's natural state continues to generate fierce controversy. What was once a wild, silt-laden torrent carving through dramatic canyons and feeding a delta ecosystem is now a carefully metered resource, its flow dictated by treaties, dams, and courtrooms rather than by snowmelt and gravity.
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Frequently Asked Questions
Who is Colorado River?
Colorado River is a major waterway of the arid Southwest, stretching roughly 1,450 miles from its Rocky Mountain headwaters in Colorado all the way down to the Gulf of California in northern Mexico. It ranks as the fifth-longest river in the United States.
What are Colorado River's powers/role?
The river supplies drinking and agricultural water to around 40 million people across seven U.S. states and two Mexican states. Its course also carves dramatic canyons, hosts eleven U.S. National Parks, and supports a thriving whitewater-recreation scene.
How does Colorado River's story end?
After winding through the Grand Canyon and crossing vast desert stretches, the river finally pours into the Colorado River Delta at the very tip of the Gulf of California, where its freshwater meets the sea.
Why is Colorado River important?
In an otherwise water-starved region, it is the backbone of regional water security, feeding cities, farms, and ecosystems across its sprawling watershed. Landmark infrastructure like Hoover Dam (finished in 1935) and the resulting Lake Mead further cement its role in managing that scarce resource.
Who are Colorado River's closest allies?
Its principal tributaries—the Green, Gunnison, Dolores, San Juan, and Little Colorado rivers—feed into the main channel and dramatically expand the watershed it drains.
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