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201-630: The Colorado River Delta is the region where the Colorado River once flowed into the Gulf of California (also known as the Sea of Cortez) in eastern Mexicali Municipality in the north of the state of Baja California , in northwestern Mexico . The delta is part of a larger geologic region called the Salton Trough . Historically, the interaction of the river's flow and the ocean's tide created
402-585: A Biosphere Nature reserve in June 1993. Within this 12,000 km (3,000,000 acres), over 4,000 km (990,000 acres) nearest the Colorado River Delta are designated as the Reserve "core area", with the remaining 8,000 km (2,000,000 acres) of open water and shoreline designated as a "buffer area". UNESCO considers areas for designation as Biosphere Reserves only after the nation in which
603-569: A $ 3,000-per-day fine to be assessed for any delay. To meet the deadline, Six Companies had to complete work by early 1933, since only in late fall and winter was the water level in the river low enough to safely divert. Tunneling began at the lower portals of the Nevada tunnels in May 1931. Shortly afterward, work began on two similar tunnels in the Arizona canyon wall. In March 1932, work began on lining
804-403: A Biosphere Reserve, 2,500 km (620,000 acres) within Colorado River Delta (Humedales del Delta del Río Colorado) are designated as a Ramsar Wetland under the U.N. Convention on Wetlands . Ramsar Wetlands are wetlands of international importance in terms of their ecology, botany, zoology, limnology or hydrology. The U.N. designation is considered following a nomination by the nation in which
1005-443: A dynamic environment, supporting freshwater, brackish , and saltwater species. Within the delta region, the river split into multiple braided channels and formed a complex estuary and terrestrial ecosystems . The use of water upstream and the accompanying reduction of freshwater flow has resulted in the loss of most of the wetlands of the area, as well as drastic changes to the aquatic ecosystems - an ecosystem collapse . Until
1206-464: A few decades before collapsing or being washed away. Failure of the lava dams caused by erosion, leaks and cavitation caused catastrophic floods, which may have been some of the largest ever to occur in North America, rivaling the late- Pleistocene Missoula Floods of the northwestern United States. Mapping of flood deposits indicate that crests as high as 700 feet (210 m) passed through
1407-580: A few notable exceptions, such as the Blackrocks reach where the river is nearly 100 feet (30 m) deep. In a few areas, such as the marshy Kawuneeche Valley near the headwaters and the Grand Valley, it exhibits braided characteristics. From Grand Junction, the Colorado turns northwest before cutting southwest across the eponymous Colorado Plateau , a vast area of high desert centered at
1608-491: A flash flood while looking for an ideal spot for the dam was the second person. The official list's final death occurred on December 20, 1935, when Patrick Tierney, electrician's helper and the son of J.G. Tierney, fell from one of the two Arizona-side intake towers. Included in the fatality list are three workers who took their own lives on site, one in 1932 and two in 1933. Of the 112 fatalities, 91 were Six Companies employees, three were Bureau of Reclamation employees, and one
1809-449: A form by only 1 inch (25 mm), and Six Companies engineers would not have permitted a flaw caused by the presence of a human body. A total of 3,250,000 cubic yards (2,480,000 cubic meters) of concrete was used in the dam before concrete pouring ceased on May 29, 1935. In addition, 1,110,000 cu yd (850,000 m ) were used in the power plant and other works. More than 582 miles (937 km) of cooling pipes were placed within
2010-847: A hundred green lagoons offered the most pleasant and least speedy path to the Gulf. Today, conditions in the delta have changed. Like other desert river deltas, such as the Nile Delta and the Indus River Delta , the Colorado River delta has been greatly altered by human activity. Decades of dam construction and water diversions in the United States and Mexico have reduced the delta to a remnant system of small wetlands and brackish mudflats. As reservoirs filled behind dams and captured floodwaters, freshwater could no longer reach
2211-403: A large concrete structure had never been built before, and some of the techniques used were unproven. The torrid summer weather and lack of facilities near the site also presented difficulties. Nevertheless, Six Companies turned the dam over to the federal government on March 1, 1936, more than two years ahead of schedule. Hoover Dam impounds Lake Mead and is located near Boulder City, Nevada ,
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#17327660209642412-577: A large system of irrigation canals making use of the Salt River . Both civilizations supported large populations at their height, with 6,000–15,000 in Chaco Canyon and as many as 30,000–200,000 Hohokam. Puebloan and Hohokam settlements were abruptly abandoned in the 1400s CE, due both to over-exploitation of natural resources such as timber, and severe drought that made it impossible to maintain irrigation systems. Many Puebloans migrated east to
2613-752: A military advantage over Goshutes and Southern Paiutes that were slower to adopt horses. The Navajo also adopted a culture of livestock herding as they acquired sheep and goats from the Spanish. Juan Bautista de Anza in 1774 was the first Spaniard to reach Yuma Crossing, where he established friendly relations with the Quechan people and opened the Anza trail between Arizona and the California coast. The Spanish soon founded Mission Puerto de Purisima Concepcion and Mission San Pedro y San Pablo de Bicuner along
2814-694: A mountain-building episode known as the Laramide orogeny . The Colorado River first formed as a west-flowing stream draining the southwestern portion of the range, and the uplift also diverted the Green River, once a tributary of the Mississippi River , west towards the Colorado. About 30 to 20 million years ago, volcanic activity related to the orogeny led to the Mid-Tertiary ignimbrite flare-up , which created smaller formations such as
3015-417: A municipality originally constructed for workers on the construction project, about 30 mi (48 km) southeast of Las Vegas , Nevada. The dam's generators provide power for public and private utilities in Nevada, Arizona, and California. Hoover Dam is a major tourist attraction, with 7 million tourists a year. The heavily traveled U.S. Route 93 (US 93) ran along the dam's crest until October 2010, when
3216-588: A new record low elevation of 1,071.61 feet (326.63 m) on July 1, 2016, before beginning to rebound slowly. Under its original design, the dam would no longer be able to generate power once the water level fell below 1,050 feet (320 m), which might have occurred in 2017 had water restrictions not been enforced. To lower the minimum power pool elevation from 1,050 to 950 feet (320 to 290 m), five wide-head turbines, designed to work efficiently with less flow, were installed. Water levels were maintained at over 1,075 feet (328 m) in 2018 and 2019, but fell to
3417-443: A new record low of 1,071.55 feet (326.61 m) on June 10, 2021 and were projected to fall below 1,066 feet (325 m) by the end of 2021. Control of water was the primary concern in the building of the dam. Power generation has allowed the dam project to be self-sustaining: proceeds from the sale of power repaid the 50-year construction loan, and those revenues also finance the multimillion-dollar yearly maintenance budget. Power
3618-413: A pumping station 20 miles (32 km) downriver. Electricity from the dam's powerhouse was originally sold pursuant to a fifty-year contract, authorized by Congress in 1934, which ran from 1937 to 1987. In 1984, Congress passed a new statute which set power allocations to southern California, Arizona, and Nevada from the dam from 1987 to 2017. The powerhouse was run under the original authorization by
3819-481: A route for a proposed railroad through the canyon, which was never built. We are now ready to start on our way down the Great Unknown. Our boats, tied to a common stake, are chafing each other, as they are tossed by the fretful river. They ride high and buoyant, for their loads are lighter than we could desire. We have but a month's rations remaining… The lighting of the boats has this advantage: they will ride
4020-493: A set of 1-inch (25 mm) steel pipes; cool river water would be poured through the pipes, followed by ice-cold water from a refrigeration plant. When an individual block had cured and had stopped contracting, the pipes were filled with grout . Grout was also used to fill the hairline spaces between columns, which were grooved to increase the strength of the joints. The concrete was delivered in huge steel buckets 7 feet high (2.1 m) and almost 7 feet in diameter; Crowe
4221-490: A short run south, the river turns west below Grand Lake , the largest natural lake in the state. For the first 250 miles (400 km) of its course, the Colorado carves its way through the mountainous Western Slope , a sparsely populated region defined by the portion of the state west of the Continental Divide . As it flows southwest, it gains strength from many small tributaries, as well as larger ones including
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#17327660209644422-474: A significant distance from the river. The Puebloan people built many multi-story pueblos or "great houses", and developed complex distribution systems to supply drinking and irrigation water in Chaco Canyon in northwestern New Mexico and Mesa Verde in southwest Colorado. The Hohokam , present in the modern Phoenix area since about 0 CE, experienced prolific growth around 600-700 CE as they constructed
4623-474: Is at Imperial Dam , where over 90 percent of the river's flow is moved into the Gila Gravity Canal and Yuma Area Project, and the much bigger All-American Canal to irrigate California's Imperial Valley , the most productive winter agricultural region in the United States. Below Imperial Dam, only a small portion of the Colorado River makes it beyond Yuma, Arizona , and the confluence with
4824-425: Is currently in place which aims to rejuvenate the wetlands by releasing a pulse of water down the river delta. The delta supports a variety of wildlife, including several threatened and endangered species. Mexico's Environmental Regulations on Endangered Species lists the following endangered species found in the terrestrial and aquatic regions of the delta (Diario Officiel, 1994): Although not extensively studied,
5025-476: Is estimated at 14.7 million acre-feet (18.1 km ), or an annualized discharge of 20,300 cu ft/s (570 m /s), for the 1906–2023 period. River flows at the Lees Ferry stream gauge, about halfway along the length of the Colorado and 16 miles (26 km) below Glen Canyon Dam, are used to determine water allocations in the Colorado River basin. Flows originating above Lees Ferry represent
5226-526: Is generated in step with and only with the release of water in response to downstream water demands. Lake Mead and downstream releases from the dam also provide water for both municipal and irrigation uses. Water released from the Hoover Dam eventually reaches several canals. The Colorado River Aqueduct and Central Arizona Project branch off Lake Havasu while the All-American Canal
5427-448: Is not subject to alkali–silica reaction (ASR), as the Hoover Dam builders happened to use nonreactive aggregate, unlike that at downstream Parker Dam , where ASR has caused measurable deterioration. With most work finished on the dam itself (the powerhouse remained uncompleted), a formal dedication ceremony was arranged for September 30, 1935, to coincide with a western tour being made by President Franklin D. Roosevelt . The morning of
5628-796: Is now known as the Long Walk and while enduring appalling conditions at Fort Sumner. After the failure of the Army to maintain the reservation there, the Treaty of Bosque Redondo established the Navajo Nation in the Four Corners, where the Navajo were allowed to return in 1868. Gold and silver were also discovered in the Upper Basin, beginning with the 1859 Blue River strike that led to
5829-758: Is only 2–3 percent of the entire basin. Urban areas cover less than 1 percent. Climate in the Colorado River Basin ranges from subtropical hot desert at southern, lower elevations to alpine in the Rocky Mountains. Mean monthly high temperatures are 25.3 °C (77.5 °F) in the Upper Basin and 33.4 °C (92.1 °F) in the Lower Basin, and lows average −3.6 and 8.9 °C (25.5 and 48.0 °F), respectively. Annual precipitation averages 6.5 inches (164 mm), ranging from over 60 inches (1,500 mm) in some areas of
6030-589: Is owned by Union Pacific . As late as 1921, the Colorado River upstream from the confluence with the Green River in Utah was still known as the Grand River. For over a decade, U.S. Representative Edward T. Taylor of Colorado had petitioned the Congressional Committee on Interstate and Foreign Commerce to rename the Grand River as the Colorado River. Representatives from Wyoming, Utah, and
6231-571: Is significantly more pronounced in the Lower Basin, where it has a strong impact on monsoonal rainfall. Runoff patterns across the Colorado River Basin reflect this; most of the perennial tributaries originate in the Upper Basin, while tributaries in the Lower Basin are either ephemeral (such as the Little Colorado River) or highly seasonal (such as the Gila and Salt rivers). As of 2010, approximately 13 million people lived within
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6432-575: Is supplied by the Imperial Dam . In total, water from Lake Mead serves 18 million people in Arizona, Nevada, and California and supplies the irrigation of over 1,000,000 acres (400,000 ha) of land. In 2018, the Los Angeles Department of Water and Power (LADWP) proposed a $ 3 billion pumped-storage hydroelectricity project—a "battery" of sorts—that would use wind and solar power to recirculate water back up to Lake Mead from
6633-544: Is the second longest and drains a greater area than the Green, but has a significantly lower flow because of a more arid climate and larger diversions for irrigation and cities. Both the Gunnison and San Juan rivers, which derive most of their water from Rocky Mountains snowmelt, contribute more water than the Gila contributed naturally. The Colorado River Basin consists of 246,000 square miles (640,000 km ), making it
6834-735: Is unknown. The Grand River above the confluence with the Gunnison River was also called the Bunkara River, the Blue River, or the North Fork of the Grand River until the 1870s. By the early 1900s the name "Grand River" had been attached to the entire stream as far as Grand Lake, which was then considered its official source. Although the Grand River was renamed the Colorado in 1921, its name survives in numerous places such as Grand County and Grand Junction, Colorado. In 1848
7035-534: The Baja California – Sonora border. Since 1960, the stretch of the Colorado between here and the Gulf of California has been dry or a trickle formed by irrigation return flows. The Hardy River provides most of the flow into the Colorado River Delta , a vast alluvial floodplain covering about 3,000 square miles (7,800 km ) of northwestern Mexico. A large estuary is formed here before
7236-606: The Blue , Eagle and Roaring Fork rivers. After passing through De Beque Canyon , the Colorado emerges from the Rockies into the Grand Valley , a major farming and ranching region where it meets one of its largest tributaries, the Gunnison River , at Grand Junction . Most of the upper river is a swift whitewater stream ranging from 200 to 500 feet (60 to 150 m) wide, the depth ranging from 6 to 30 feet (2 to 9 m), with
7437-556: The Chiricahua Mountains in Arizona and deposited massive amounts of volcanic ash and debris over the watershed. The Colorado Plateau first began to rise during the Eocene , between about 55 and 34 million years ago, but did not attain its present height until about 5 million years ago, about when the Colorado River established its present course into the Gulf of California. The time scale and sequence over which
7638-659: The Colorado River Indian Tribes . As the American frontier expanded into the Colorado Plateau, an effort to expel the Navajo from the Four Corners region was begun by General James Henry Carleton , who in 1864 enlisted mountain man Kit Carson to lead a campaign against the Navajo. Carson, with the help of the Navajo's Ute enemies, captured more than 8,000 Navajo and forcibly marched them to Fort Sumner , New Mexico. Hundreds died during what
7839-627: The Four Corners of the southwestern United States. Here, the climate becomes significantly drier than that in the Rocky Mountains, and the river becomes entrenched in progressively deeper gorges of bare rock, beginning with Ruby Canyon and then Westwater Canyon as it enters Utah , now once again heading southwest. 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
8040-556: The Fremont culture period (0–1300 CE). The Ancient Puebloan culture, also known as Anasazi or Hisatsinom, were descended from the Desert Archaic culture and became established in the Four Corners region around 1000 CE. While there is much evidence of ancient habitation along the Colorado River, including stone dwellings, petroglyphs and pottery in places such as Glen Canyon, the first major agriculture-based societies arose
8241-799: The Grand Mesa ; the Weenuchiu lived along the San Juan River, and the Parianuche and Yamparika lived in the Yampa, White and Duchesne River valleys. The Ute ranged as far as the river’s headwaters; one Ute story recounts a battle with the Arapaho at Grand Lake, which they believe still hosts the spirits of the deceased. Starting in the 1500s, the Spanish began to explore and colonize western North America. Francisco de Ulloa may have been
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8442-528: The Great Depression , it 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 100 lives. In bills passed by Congress during its construction, it was referred to as the Hoover Dam, after President Herbert Hoover , but was named Boulder Dam by the Roosevelt administration. In 1947,
8643-627: The Great Salt Lake and Sevier Lake watersheds. To the south, the Colorado River Basin borders several watersheds in Mexico draining into the Gulf of California, including the Sonoyta , Concepción , and Yaqui rivers. Much of the basin is at high elevation; the mean elevation is 5,500 feet (1,700 m). Lees Ferry, more than halfway along the Colorado River from its source, is 3,150 feet (960 m) above sea level. The highest point in
8844-652: The Hoover Dam Bypass opened. As the United States developed the Southwest, the Colorado River was seen as a potential source of irrigation water. An initial attempt at diverting the river for irrigation purposes occurred in the late 1890s, when land speculator William Beatty built the Alamo Canal just north of the Mexican border; the canal dipped into Mexico before running to a desolate area Beatty named
9045-684: The Imperial Valley . Though water from the Alamo Canal allowed for the widespread settlement of the valley, the canal proved expensive to operate. After a catastrophic breach that caused the Colorado River to fill the Salton Sea , the Southern Pacific Railroad spent $ 3 million in 1906–07 to stabilize the waterway, an amount it hoped in vain that it would be reimbursed for by the federal government. Even after
9246-478: 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. 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
9447-627: The Mogollon Rim in central Arizona. These high plateaus and escarpments, often exceeding 9,000 feet (2,700 m) in elevation, form the northern and southern edges of the Colorado Plateau geological province. Developed land use in the basin is mostly irrigated agriculture, chiefly in the Grand Valley , the Lower Colorado River Valley , and the Salt River Valley , but the total area of crop and pasture land
9648-531: The Monterey submarine canyon . Crustal extension in the Basin and Range Province began about 20 million years ago and the modern Sierra Nevada began forming about 10 million years ago, eventually diverting the Colorado southwards towards the Gulf. As the Colorado Plateau continued to rise between 5 and 2.5 million years ago, the river maintained its ancestral course (as an antecedent stream ) and began to cut
9849-537: The Parker , Shasta and Grand Coulee dams and power plants. True's work on the Hoover Dam was humorously referred to in a poem published in The New Yorker , part of which read, "lose the spark, and justify the dream; but also worthy of remark will be the color scheme". Complementing Kaufmann and True's work, sculptor Oskar J. W. Hansen designed many of the sculptures on and around the dam. His works include
10050-427: The Southern Paiute ) and the Kumeyaay inhabited the desert to the river’s west. Those living along the lower Colorado River depended more on fishing and floodplain agriculture than on irrigation, and mostly did not live in permanent settlements. The site of modern-day Yuma has been an important river crossing since ancient times, as the channel here is much narrower compared to the expansive, swampy river bottoms to
10251-418: The United States Geological Survey objected, noting that the Green River was longer and drained a larger area. Taylor argued that the Grand River should be considered the main stream, as it carried the larger volume of water. Taylor felt “slighted” that the Colorado River, as named, did not begin in the state of Colorado, and “he wasn’t going to let Utah or Wyoming lay claim to the river’s headwaters, despite
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#173276602096410452-543: The southwestern willow flycatcher , the fulvous whistling duck , and the sandhill crane . The Gulf of California lies within the jurisdictional boundaries of Mexico and its states of Baja California and Sonora . In 1974, the Mexican government designated portions of the upper Gulf and lower Colorado River Delta as a reserve zone. The United Nations Educational, Scientific and Cultural Organization (UNESCO) designated over 12,000 km (3,000,000 acres) of Gulf of California and Colorado River Delta Biosphere Reserve as
10653-407: The "Wobblies", they formed a committee to represent them with the company. The committee drew up a list of demands that evening and presented them to Crowe the following morning. He was noncommittal. The workers hoped that Crowe, the general superintendent of the job, would be sympathetic; instead, he gave a scathing interview to a newspaper, describing the workers as "malcontents". On the morning of
10854-442: 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
11055-466: The 1500s. Navajo Mountain and Rainbow Bridge in the Glen Canyon area came to hold particular religious significance for the Navajo, and the nearby confluence of the Colorado and San Juan River is regarded as the birthplace of clouds and rain. The Ute also became established in the Colorado Plateau around 1500 CE, although they had inhabited more northerly parts of the Colorado basin (modern Wyoming and northern Colorado) since at least 0 CE. They are
11256-418: The 9th, Crowe met with the committee and told them that management refused their demands, was stopping all work, and was laying off the entire work force, except for a few office workers and carpenters. The workers were given until 5 p.m. to vacate the premises. Concerned that a violent confrontation was imminent, most workers took their paychecks and left for Las Vegas to await developments. Two days later,
11457-562: The Arizona–Nevada and Arizona– California borders. After leaving the confines of the Black Canyon , the river emerges from the Colorado Plateau into the Lower Colorado River Valley (LCRV), a desert region dependent on irrigation agriculture and tourism and also home to several major Indian reservations . The river widens here to a broad, moderately deep waterway averaging 500 to 1,000 feet (150 to 300 m) wide and reaching up to 0.25 miles (400 m) across, with depths ranging from 8 to 60 feet (2 to 20 m). Before channelization of
11658-410: The Army had driven out the remaining pockets of Ute resistance on the Western Slope, officially opening the Grand River country to settlement, and the town of Grand Junction was incorporated a year later. The Denver and Rio Grande Western Railroad (D&RGW) quickly expanded into this area to serve mining boomtowns, crossing the Rockies to the south via the Black Canyon of the Gunnison River . By 1883
11859-435: The Colorado River Basin is 14,321-foot (4,365 m) Uncompahgre Peak in Colorado's San Juan Mountains , while some water from the river drains via irrigation run-off into California's Salton Sea , 236 feet (72 m) below sea level. About 72 percent of the Colorado River Basin is classified as arid, with the Sonoran and Mojave deserts covering the southern portion and the Colorado Plateau encompassing much of
12060-401: The Colorado River Basin. Other significant cities include Tucson, Arizona , St. George, Utah and Flagstaff, Arizona . Due to the rugged and inhospitable topography through which the river flows, there are only a few major towns along the Colorado River itself, including Grand Junction, Colorado and Yuma, Arizona . The unimpaired annual runoff of the Colorado River at Lees Ferry, Arizona
12261-408: The Colorado River Delta almost entirely dry except for small amounts of agricultural wastewater. As recently as the Cretaceous period about 100 million years ago, much of western North America was still part of the Pacific Ocean . Tectonic forces from the collision of the Farallon Plate with the North American Plate pushed up the Rocky Mountains between 50 and 75 million years ago in
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#173276602096412462-549: The Colorado River Delta prior to the early 20th century. Up to 90 percent of the river's flow originates as snowmelt from the Rocky Mountains and other smaller mountain ranges of the Colorado Plateau. Natural seasonal flows at its mouth varied widely, often exceeding 100,000 cu ft/s (2,800 m /s) in the spring melt and falling as low as 2,500 cu ft/s (71 m /s) in winter. Snowmelt typically begins in April, peaks in May or June, and can extend into August in wet years. Monsoon rainstorms often occur in
12663-405: The Colorado River Delta, the basin extends into Sonora at a few locations further east, including the headwaters of the Santa Cruz River and San Pedro River (both tributaries of the Gila River). For hydrological management purposes, the Colorado River Basin is divided into the Upper Basin (the drainage area above Lees Ferry), and the Lower Basin . The Upper Basin covers only 45 percent of
12864-431: The Colorado River as a federal concern because the river's basin covered several states, and the river eventually entered Mexico. Though the Fall-Davis report called for a dam "at or near Boulder Canyon", the Reclamation Service (which was renamed the Bureau of Reclamation the following year) found that canyon unsuitable. One potential site at Boulder Canyon was bisected by a geologic fault ; two others were so narrow there
13065-424: The Colorado River basin, while about 40 million people live in areas supplied by Colorado River water. Colorado River basin states are among the fastest-growing in the US; the population of Nevada alone increased by about 66 percent between 1990 and 2000 as Arizona grew by some 40 percent. Phoenix, Arizona , Las Vegas, Nevada and Mexicali, Baja California are the largest cities by population within
13266-425: The Colorado River near the junction with the Dolores River , naming the larger river “Rio San Rafael”. They later forded the Colorado in southeastern Utah at Crossing of the Fathers , now submerged in Lake Powell. In the 1820s, American fur trappers along the upper Green River in Wyoming (known to them as the "Seedskeedee" or variants thereof), seeking a route to export furs to the coast, surmised that this and what
13467-433: The Colorado River usually passes through the turbines. The spillways and outlet works (jet-flow gates) are rarely used. The jet-flow gates, located in concrete structures 180 feet (55 m) above the river and also at the outlets of the inner diversion tunnels at river level, may be used to divert water around the dam in emergency or flood conditions, but have never done so, and in practice are used only to drain water from
13668-482: 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. The Colorado begins at La Poudre Pass in the Never Summer Mountains in Rocky Mountain National Park , 10,184 ft (3,104 m) above sea level. After
13869-485: The Colorado empties into the Gulf about 75 miles (120 km) south of Yuma. Occasionally the International Boundary and Water Commission allows a springtime pulse flow to recharge the delta. Before 20th-century development dewatered the lower Colorado, a major tidal bore was present in the delta and estuary; the first historical record was made by the Croatian missionary in Spanish service Father Ferdinand Konščak on July 18, 1746. During spring tide conditions,
14070-416: 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 the Colorado from the east. The Colorado then enters northern Arizona , where since the 1960s Glen Canyon Dam near Page has flooded
14271-434: The Colorado in the 20th century, the lower river was subject to frequent course changes caused by seasonal flow variations. Joseph C. Ives , who surveyed the lower river in 1861, wrote that "the shifting of the channel, the banks, the islands, the bars is so continual and rapid that a detailed description, derived from the experiences of one trip, would be found incorrect, not only during the subsequent year, but perhaps in
14472-466: 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
14673-521: The Continental Divide, but ran out of money before even reaching Utah. In 1931 the D&;RGW completed the "Dotsero Cutoff" linking Glenwood Springs to the D&SL route at Bond, Colorado , finally completing the direct Denver–Salt Lake link with its acquisition of the bankrupt D&SL. The Gunnison River route was eventually abandoned in favor of the shorter Colorado River route, which today
14874-473: The Glen Canyon reach of the river, forming Lake Powell for hydroelectricity generation. In Arizona, the river passes Lee's Ferry , an important crossing for early explorers and settlers and since the early 20th century the principal point where Colorado River flows are measured for apportionment to the seven U.S. and two Mexican states in the basin. Downstream, the river enters Marble Canyon ,
15075-506: The Grand Canyon, reaching peak discharges as great as 17 million cubic feet per second (480,000 m /s). Small numbers of Paleo-Indians of the Clovis and Folsom cultures inhabited the Colorado Plateau as early as 10,000 BCE, with populations beginning to increase in the Desert Archaic period (6000 BCE–0 CE). While most early inhabitants were hunter-gatherers, evidence of agriculture, masonry dwellings and petroglyphs begins with
15276-540: The Grand Canyon. Antecedence played a major part in shaping other peculiar geographic features in the watershed, including the Dolores River's bisection of Paradox Valley in Colorado and the Green River's cut through the Uinta Mountains in Utah. Sediments carried from the plateau by the Colorado River created a vast delta made of more than 10,000 cubic miles (42,000 km ) of material that walled off
15477-412: The Grand Canyon. At least 13 lava dams were formed, the largest of which was more than 2,300 feet (700 m) high, backing the river up for nearly 500 miles (800 km) to present-day Moab, Utah. The lack of associated sediment deposits along this stretch of the Colorado River, which would have accumulated in the impounded lakes over time, suggests that most of these dams did not survive for more than
15678-554: The Los Angeles Department of Water and Power and Southern California Edison; in 1987, the Bureau of Reclamation assumed control. In 2011, Congress enacted legislation extending the current contracts until 2067, after setting aside 5% of Hoover Dam's power for sale to Native American tribes, electric cooperatives, and other entities. The new arrangement began on October 1, 2017. The Bureau of Reclamation reports that
15879-467: The Lower Basin from August through October, contributing much of the flow in tributaries below Lees Ferry and often causing flash flooding . Since the initial closure of Hoover Dam in 1934, lower Colorado River flows have been greatly moderated, with monthly means below the dam ranging from 16,400 cu ft/s (460 m /s) in May to 11,200 cu ft/s (320 m /s) in October. Upstream of
16080-657: The Moab Valley between a pair of 1,000-foot (300 m) sandstone cliffs. In Utah, the Colorado flows primarily through the " slickrock " country, which is characterized by its narrow canyons and unique "folds" created by the tilting of sedimentary rock layers along faults. This is one of the most inaccessible regions of the continental United States. Below the confluence with the Green River , its largest tributary, in Canyonlands National Park ,
16281-588: The President's speech, in which he avoided mentioning the name of former President Hoover, who was not invited to the ceremony. To mark the occasion, a three-cent stamp was issued by the United States Post Office Department —bearing the name "Boulder Dam", the official name of the dam between 1933 and 1947. After the ceremony, Roosevelt made the first visit by any American president to Las Vegas. Most work had been completed by
16482-591: The Republic , were both formed in a continuous pour. To put such large bronzes into place without marring the highly polished bronze surface, they were placed on ice and guided into position as the ice melted. Hansen's bas-relief on the Nevada elevator tower depicts the benefits of the dam: flood control, navigation, irrigation, water storage, and power. The bas-relief on the Arizona elevator depicts, in his words, "the visages of those Indian tribes who have inhabited mountains and plains from ages distant." Excavation for
16683-630: The Rio Grande Valley, while others persisted in smaller settlements on the Colorado Plateau. Puebloan descendants include the Hopi , Zuni , Laguna and Acoma peoples of modern Arizona and New Mexico. O'odham peoples, including the Akimel O'odham (Pima) and Maricopa who continue to live in southern Arizona, are believed to be descended from the Hohokam. The lower Colorado River valley
16884-644: The Rockies to less than 4 inches (100 mm) in dry desert valleys. The Upper Basin generally receives snow and rain during the winter and early spring, while precipitation in the Lower Basin falls mainly during intense but infrequent summer thunderstorms brought on by the North American Monsoon . Precipitation is influenced by the El Niño-Southern Oscillation (ENSO) with El Niño being associated with wetter conditions and La Niña with drier conditions. The effect of ENSO
17085-535: The Rockies. Water diversions have effectively removed some tributaries entirely, including the Gila River, once the Colorado's largest tributary below Lees Ferry. Most Colorado River water is diverted in the United States, with only about 2.8 million acre-feet (3.5 km ) per year reaching Mexico since 1950. At Morelos Dam, the remaining flow is diverted to irrigate the Mexicali Valley, leaving
17286-489: The Salton Sea. The Board cautioned: "To avoid such possibilities, the proposed dam should be constructed on conservative if not ultra-conservative lines." On December 21, 1928, President Coolidge signed the bill authorizing the dam. The Boulder Canyon Project Act appropriated $ 165 million for the project along with the downstream Imperial Dam and All-American Canal , a replacement for Beatty's canal entirely on
17487-535: The Spanish called the Colorado were in fact connected. William H. Ashley made an unsuccessful attempt to navigate from the Green River to the Colorado's mouth in 1825. In 1826, Jedediah Smith arrived at the lower Colorado River, referring to it as the Seedskeedee, and proceeded upstream, exploring as far as Black Canyon. During the 1830s, various fur trappers from Wyoming made it as far downstream as Cataract Canyon and Glen Canyon, but none were able to navigate
17688-605: The Spanish language for "colored reddish" due to its heavy silt load. Starting in the central Rocky Mountains of Colorado , it 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
17889-534: The Supreme Court handed down the Wyoming v. Colorado decision undermining the claims of the upstream states, they became anxious to reach an agreement. The resulting Colorado River Compact was signed on November 24, 1922. Legislation to authorize the dam was introduced repeatedly by two California Republicans, Representative Phil Swing and Senator Hiram Johnson , but representatives from other parts of
18090-495: The U.S. Army established Fort Yuma , creating the first permanent U.S. settlement along the river. This served as a military garrison and supply point for settlers headed to California along the Southern Emigrant Trail . Due to the arduous task of ferrying supplies overland, the schooner Invincible attempted to bring supplies up the river but was thwarted by the delta’s strong tides. Steamboats were brought to
18291-507: The U.S. side of the border. It also permitted the compact to go into effect when at least six of the seven states approved it. This occurred on March 6, 1929, with Utah's ratification; Arizona did not approve it until 1944. Even before Congress approved the Boulder Canyon Project, the Bureau of Reclamation was considering what kind of dam should be used. Officials eventually decided on a massive concrete arch-gravity dam ,
18492-625: The Virgin River, enabled shipping of their produce by wagon to gold mining districts further south. Although the Mormons abandoned St. Thomas in 1871, a salt-mining industry persisted here, and steamboats operated up to nearby Rioville into the 1880s. In 1879 a group of Mormon settlers made their way to southeastern Utah, blasting the precarious Hole in the Rock Trail to cross the Colorado River at Glen Canyon, subsequently establishing
18693-557: The World (IWW or "Wobblies"), though much-reduced from their heyday as militant labor organizers in the early years of the century, hoped to unionize the Six Companies workers by capitalizing on their discontent. They sent eleven organizers, several of whom were arrested by Las Vegas police. On August 7, 1931, the company cut wages for all tunnel workers. Although the workers sent the organizers away, not wanting to be associated with
18894-482: The arch-gravity as was proposed for the Black Canyon dam, opponents claimed that the Black Canyon dam's safety could not be guaranteed. Congress authorized a board of engineers to review plans for the proposed dam. The Colorado River Board found the project feasible, but warned that should the dam fail, every downstream Colorado River community would be destroyed, and that the river might change course and empty into
19095-562: The assistance of the National Laboratory of Anthropology, True researched authentic decorative motifs from Indian sand paintings, textiles, baskets and ceramics. The images and colors are based on Native American visions of rain, lightning, water, clouds, and local animals—lizards, serpents, birds—and on the Southwestern landscape of stepped mesas. In these works, which are integrated into the walkways and interior halls of
19296-582: The beginning of the Grand Canyon , passing under the Navajo Bridges on a now southward course. Below the confluence with the Little Colorado River , the river swings west into Granite Gorge, the most dramatic portion of the Grand Canyon, where the river cuts up to one mile (1.6 km) into the Colorado Plateau, exposing some of the oldest visible rocks on Earth, dating as long ago as 2 billion years. The 277 miles (446 km) of
19497-416: The bid documents in nearly as much detail as the dam itself. The upper cofferdam was 96 ft (29 m) high, and 750 feet (230 m) thick at its base, thicker than the dam itself. It contained 650,000 cubic yards (500,000 m ) of material. When the cofferdams were in place and the construction site was drained of water, excavation for the dam foundation began. For the dam to rest on solid rock, it
19698-461: The bottom, narrowing to 45 ft (14 m) at the top, leaving room for a highway connecting Nevada and Arizona. On January 10, 1931, the Bureau made the bid documents available to interested parties, at five dollars a copy. The government was to provide the materials, and the contractor was to prepare the site and build the dam. The dam was described in minute detail, covering 100 pages of text and 76 drawings. A $ 2 million bid bond
19899-461: The bypass tunnels, as the tunnel had to be used to take in irrigation water until the powerhouse went into operation. There were 112 deaths reported as associated with the construction of the dam. The first was Bureau of Reclamation employee Harold Connelly who died on May 15, 1921, after falling from a barge while surveying the Colorado River for an ideal spot for the dam. Surveyor John Gregory ("J.G.") Tierney, who drowned on December 20, 1922, in
20100-573: The canyon wall, to house 480 single men at what became known as River Camp. Workers with families were left to provide their own accommodations until Boulder City could be completed, and many lived in Ragtown. The site of Hoover Dam endures extremely hot weather, and the summer of 1931 was especially torrid, with the daytime high averaging 119.9 °F (48.8 °C). Sixteen workers and other riverbank residents died of heat prostration between June 25 and July 26, 1931. The Industrial Workers of
20301-468: The central portion. The Colorado Plateau is home to most of the major canyon systems formed by the Colorado River and its tributaries, particularly those of the Green and San Juan rivers. About 23 percent of the basin is forest, with the largest area in the Rocky Mountains; other significant forested areas include the Kaibab , Aquarius , and Markagunt plateaus in southern Utah and northern Arizona, and
20502-432: The channel, we know not; what walls rise over the river, we know not; Ah, well! we may conjecture many things. The men talk as cheerfully as ever; jests are bandied about freely this morning; but to me the cheer is somber and the jests are ghastly. In 1858, gold was discovered on the Gila River east of Yuma, then along the Colorado River at El Dorado Canyon, Nevada and La Paz, Arizona . As prospectors and settlers entered
20703-490: The clocks display the same time for more than half the year. At Kaufmann's request, Denver artist Allen Tupper True was hired to handle the design and decoration of the walls and floors of the new dam. True's design scheme incorporated motifs of the Navajo and Pueblo tribes of the region. Although some were initially opposed to these designs, True was given the go-ahead and was officially appointed consulting artist. With
20904-589: The community of Bluff . Due to the dry climate, these settlements depended heavily on irrigation. In central Arizona, settlers uncovered and re-established canals previously used by the Hohokam. Following tensions between Mormon settlers and the U.S. government in the Utah War , a local militia including John D. Lee perpetrated the 1857 Mountain Meadows Massacre , in which 120 non-Mormon settlers were killed. Fearing retribution, Lee moved in 1870 to
21105-419: The concrete. Overall, there is enough concrete in the dam to pave a two-lane highway from San Francisco to New York. Concrete cores were removed from the dam for testing in 1995; they showed that "Hoover Dam's concrete has continued to slowly gain strength" and the dam is composed of a "durable concrete having a compressive strength exceeding the range typically found in normal mass concrete". Hoover Dam concrete
21306-420: The construction of major dams along its route, the Colorado River fed one of the largest desert estuaries in the world. Spread across the northernmost end of the Gulf of California, the Colorado River delta's vast riparian , freshwater, brackish, and tidal wetlands once covered 7,810 km (1,930,000 acres) and supported a large population of plant, bird, aquatic, and terrestrial life. Because most of
21507-481: The construction period. The initial plans for the facade of the dam, the power plant, the outlet tunnels and ornaments clashed with the modern look of an arch dam. The Bureau of Reclamation, more concerned with the dam's functionality, adorned it with a Gothic -inspired balustrade and eagle statues. This initial design was criticized by many as being too plain and unremarkable for a project of such immense scale, so Los Angeles-based architect Gordon B. Kaufmann , then
21708-485: The country considered the project as hugely expensive and one that would mostly benefit California. The 1927 Mississippi flood made Midwestern and Southern congressmen and senators more sympathetic toward the dam project. On March 12, 1928, the failure of the St. Francis Dam , constructed by the city of Los Angeles, caused a disastrous flood that killed up to 600 people. As that dam was a curved-gravity type, similar in design to
21909-454: The course of a week, or even a day." The LCRV is one of the most densely populated areas along the river, and there are numerous towns including Bullhead City, Arizona , Needles, California , and Lake Havasu City, Arizona . Here, several large diversions draw from the river, providing water for both local uses and distant regions including the Salt River Valley of Arizona and metropolitan Southern California . The last major U.S. diversion
22110-408: The dam (from pea-sized gravel to 9 inches [230 mm] stones), it was vital that the bucket be maneuvered to the proper column. When the bottom of the bucket opened up, disgorging 8 cu yd (6.1 m ) of concrete, a team of men worked it throughout the form. Although there are myths that men were caught in the pour and are entombed in the dam to this day, each bucket deepened the concrete in
22311-505: The dam could be built, the Colorado River needed to be diverted away from the construction site. To accomplish this, four diversion tunnels were driven through the canyon walls, two on the Nevada side and two on the Arizona side. These tunnels were 56 ft (17 m) in diameter. Their combined length was nearly 16,000 ft, or more than 3 miles (5 km). The contract required these tunnels to be completed by October 1, 1933, with
22512-628: The dam feared endless litigation. Delph Carpenter, a Colorado attorney, proposed that the seven states which fell within the river's basin (California, Nevada, Arizona, Utah, New Mexico, Colorado and Wyoming) form an interstate compact , with the approval of Congress. Such compacts were authorized by Article I of the United States Constitution but had never been concluded among more than two states. In 1922, representatives of seven states met with then- Secretary of Commerce Herbert Hoover . Initial talks produced no result, but when
22713-540: The dam is an integral component for management of the Colorado River, controlling floods and storing water for farms and cities in the lower Colorado River basin. Below the dam the river passes under the Mike O'Callaghan–Pat Tillman Memorial Bridge —which at nearly 900 feet (270 m) above the water is the highest concrete arch bridge in the Western Hemisphere —and then turns due south towards Mexico, defining
22914-399: The dam site was reinforced with grout , forming a grout curtain . Holes were driven into the walls and base of the canyon, as deep as 150 feet (46 m) into the rock, and any cavities encountered were to be filled with grout. This was done to stabilize the rock, to prevent water from seeping past the dam through the canyon rock, and to limit "uplift"—upward pressure from water seeping under
23115-400: The dam was authorized, increasing numbers of unemployed people converged on southern Nevada. Las Vegas, then a small city of some 5,000, saw between 10,000 and 20,000 unemployed descend on it. A government camp was established for surveyors and other personnel near the dam site; this soon became surrounded by a squatters' camp. Known as McKeeversville, the camp was home to men hoping for work on
23316-466: The dam wound down. When a Six Companies manager altered working times to force workers to take lunch on their own time, workers responded with a strike. Emboldened by Crowe's reversal of the lunch decree, workers raised their demands to include a $ 1-per-day raise. The company agreed to ask the Federal government to supplement the pay, but no money was forthcoming from Washington. The strike ended. Before
23517-444: The dam's total power output was placed on the grid and made arbitrarily distributable. Before water from Lake Mead reaches the turbines, it enters the intake towers and then four gradually narrowing penstocks which funnel the water down towards the powerhouse. The intakes provide a maximum hydraulic head (water pressure) of 590 ft (180 m) as the water reaches a speed of about 85 mph (140 km/h). The entire flow of
23718-405: The dam, True also reflected on the machinery of the operation, making the symbolic patterns appear both ancient and modern. With the agreement of Kaufmann and the engineers, True also devised for the pipes and machinery an innovative color-coding which was implemented throughout all BOR projects. True's consulting artist job lasted through 1942; it was extended so he could complete design work for
23919-409: The dam. The workers were under severe time constraints due to the beginning of the concrete pour. When they encountered hot springs or cavities too large to readily fill, they moved on without resolving the problem. A total of 58 of the 393 holes were incompletely filled. After the dam was completed and the lake began to fill, large numbers of significant leaks caused the Bureau of Reclamation to examine
24120-620: The dams are used to regulate flow so that water can be reliably apportioned among the users of the Colorado River Compact , and its use maximized. Most flood flows can be contained, regulated, and added to the river's capacity to sustain the Western United States ' urban centers and agriculture . Floodwaters are released only when the Bureau of Reclamation , the agency managing the dams, predicts flows that exceed
24321-568: The daring." Hansen's dedication plaza, on the Nevada abutment, contains a sculpture of two winged figures flanking a flagpole. Surrounding the base of the monument is a terrazzo floor embedded with a "star map". The map depicts the Northern Hemisphere sky at the moment of President Roosevelt's dedication of the dam. This is intended to help future astronomers, if necessary, calculate the exact date of dedication. The 30-foot-high (9.1 m) bronze figures, dubbed Winged Figures of
24522-475: The dedication, and Six Companies negotiated with the government through late 1935 and early 1936 to settle all claims and arrange for the formal transfer of the dam to the Federal Government. The parties came to an agreement and on March 1, 1936, Secretary Ickes formally accepted the dam on behalf of the government. Six Companies was not required to complete work on one item, a concrete plug for one of
24723-520: The dedication, it was moved forward three hours from 2 p.m. Pacific time to 11 a.m.; this was done because Secretary of the Interior Harold L. Ickes had reserved a radio slot for the President for 2 p.m. but officials did not realize until the day of the ceremony that the slot was for 2 p.m. Eastern Time. Despite the change in the ceremony time, and temperatures of 102 °F (39 °C), 10,000 people were present for
24924-437: The delta's significance for migratory birds is indisputable, as it is the principal freshwater marsh in the region. A total of 358 bird species have been documented in the Colorado River Delta and the upper Gulf of California region. From these, two are listed as endangered, six as threatened, and sixteen are under special protection in Mexico. Two wintering species and five breeding species have been locally extirpated, including
25125-596: The delta, in addition to the abundance of waterfowl , fish , and other marine and estuary organisms (Spamer, 1990; { Aldo Leopold , 1948}). Early explorers also encountered local people known as the Cucapá , or the people of the river. The Cucapá are descendants of the Yuman -speaking Native Indigenous peoples of the Americas and have inhabited the delta for nearly a thousand years. Spanish explorer Hernando de Alarcón made
25326-477: The delta. The construction of Hoover Dam in the 1930s marked the beginning of the modern era for the Colorado River Delta. For six years, as Lake Mead filled behind the dam, virtually no freshwater reached the delta. Even spring flooding was captured. This ecologically devastating event was repeated from 1963 to 1981 as Lake Powell filled behind the Glen Canyon Dam . With these reservoirs now filled,
25527-411: The design of which was overseen by the Bureau's chief design engineer John L. Savage . The monolithic dam would be thick at the bottom and thin near the top and would present a convex face towards the water above the dam. The curving arch of the dam would transmit the water's force into the abutments, in this case the rock walls of the canyon. The wedge-shaped dam would be 660 ft (200 m) thick at
25728-541: The diversion tunnels), and a classification used by Six Companies to avoid paying compensation claims. The site's diversion tunnels frequently reached 140 °F (60 °C), enveloped in thick plumes of vehicle exhaust gases. A total of 42 workers were recorded as having died from pneumonia and were not included in the above total; none were listed as having died from carbon monoxide poisoning. No deaths of non-workers from pneumonia were recorded in Boulder City during
25929-544: The early 20th century, the Colorado River ran free from its headwaters in the Rocky Mountains of Colorado southwest into Mexico , where it flowed into the Gulf of California . Significant quantities of nourishing silt from throughout the Colorado River Basin were carried downstream, creating the vast Colorado River Delta and preventing intrusion of seawater into the Mexicali and Imperial Valleys . Prior to
26130-658: The east side of the divide drain into the Mississippi River and Rio Grande , while nearby areas north of the Wind River Range drain into the Columbia River . The western boundary of the Colorado River Basin is formed by various ranges and plateaus that border the Great Basin , including the Uinta Mountains and Wasatch Range . Major Great Basin watersheds bordering the Colorado River Basin are
26331-590: The energy generated under the contracts ending in 2017 was allocated as follows: The dam is protected against over-topping by two spillways . The spillway entrances are located behind each dam abutment , running roughly parallel to the canyon walls. The spillway entrance arrangement forms a classic side-flow weir with each spillway containing four 100-foot-long (30 m) and 16-foot-wide (4.9 m) steel-drum gates. Each gate weighs 5,000,000 pounds (2,300 metric tons) and can be operated manually or automatically. Gates are raised and lowered depending on water levels in
26532-519: The fact that the Green River is the larger drainage basin.” On July 25, 1921, President Warren G. Harding signed House Joint Resolution 32 - “To change the name of the Grand River in Colorado and Utah to the Colorado River.” Hoover Dam Hoover Dam 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 . Constructed between 1931 and 1936, during
26733-468: The ferry obsolete. The Denver and Salt Lake Railway (D&SL), incorporated in 1902, sought to provide a more direct connection between Denver and Salt Lake City than either the transcontinental railroad through Wyoming or the D&RGW’s route via Black Canyon and Durango. The D&SL completed a rail line into the upper headwaters of the Colorado River and blasted the Moffat Tunnel under
26934-468: The first European to see the river, when in 1536 he sailed to the head of the Gulf of California. In 1540 García López de Cárdenas became the first European to see the Grand Canyon, during Coronado 's expedition to find the Seven Cities of Gold ("Cibola"). Cárdenas was apparently unimpressed with the canyon, greatly underestimating its size, and left in disappointment with no gold to be found. In
27135-408: The first known inhabitants of this part of the Rocky Mountains, and made use of an extensive network of trails crisscrossing the mountains to move between summer and winter camps. The Ute were divided into numerous bands with separate territories but shared a common language and customs. The Uncompahgre or Tabeguache lived around the confluence of the upper Colorado and Gunnison Rivers, an area including
27336-452: The first part of non-natives to travel the length of the Grand Canyon, and the first to successfully travel by boat from the upper Green River to the lower Colorado. Powell led a second expedition in 1871, with financial backing from the U.S. government, and continued to conduct geographical and botanical surveys across the region until the 1890s. Another Grand Canyon river expedition was led in 1889-1890 by Robert Brewster Stanton to survey
27537-532: The first recorded contact with the Cucapá in 1540 and reported seeing many thousands. The Cucapá used the delta floodplain extensively for harvesting Palmer's saltgrass ( Distichlis palmeri ), a wild grain that grows in salty soil, and for cultivating maize (corn), beans , and squash . On the map the Delta was bisected by the river, but in fact the river was nowhere and everywhere, for he could not decide which of
27738-415: The first three Allis Chalmers built Francis turbine - generators , all on the Nevada side, began operating. In March 1937, one more Nevada generator went online and the first Arizona generator by August. By September 1939, four more generators were operating, and the dam's power plant became the largest hydroelectricity facility in the world. The final generator was not placed in service until 1961, bringing
27939-582: The founding of Breckenridge, Colorado . Up until the 1860s, southwestern Colorado had remained relatively untouched by U.S. westward expansion, as the Americans had recognized Ute sovereignty by treaty. Following the 1861 carving out of Colorado Territory and further mineral strikes including Ouray and Telluride , Ute leaders were coerced into signing the 1873 Brunot Agreement , in which they lost rights to most of their land. A flood of mineral prospecting and settlement ensued in western Colorado. By 1881,
28140-485: The full length of the river. In 1843 John C. Frémont explored the Great Basin and conclusively determined no Buenaventura River flowed west to California; thus, the direction of river flow must be southwest. By the early 19th century, the stretch of the Colorado above the confluence of the Green River at Cataract Canyon , Utah, became known to fur trappers as the "Grand River", though the exact origin of this name
28341-539: The headquarters for the dam construction, closing its many speakeasies when the decision maker, Secretary of the Interior Ray Wilbur , came to town. Instead, Wilbur announced in early 1930 that a model city was to be built in the desert near the dam site. This town became known as Boulder City, Nevada . Construction of a rail line joining Las Vegas and the dam site began in September 1930. Soon after
28542-536: The intermittent Gila River —which carries runoff from western New Mexico and most of Arizona–before defining 24 miles (39 km) of the Mexico–United States border . At Morelos Dam , the entire remaining flow of the Colorado is diverted to irrigate the Mexicali Valley , among Mexico's most fertile agricultural lands. Below San Luis Río Colorado , the Colorado passes entirely into Mexico, defining
28743-753: The land area of the Colorado River Basin, but contributes 92 percent of the runoff. The entire eastern boundary of the Colorado River Basin runs along the North American Continental Divide and is defined largely by the Rocky Mountains and the Rio Grande Basin . The Wind River Range in Wyoming marks the northern extent of the basin, and is separated from the Colorado Rockies by the endorheic Great Divide Basin in southwestern Wyoming. Streams that are nearby
28944-513: The lower Colorado River. However, Spanish attempts to control the crossing led to the 1781 Yuma revolt, in which over 100 soldiers and colonists were killed, and the settlements were abandoned. The Quechan blocked foreigners’ use of the crossing until the arrival of American mountain men and fur trappers in the 1820s. The name Rio Colorado first appears in 1701, on the map "Paso por Tierra a la California" published by missionary Eusebio Kino , who also determined during that time that Baja California
29145-565: The majority of Colorado River runoff. Tributaries between there and Imperial Dam near the US–Mexico border contribute a further 1.1 million acre-feet (1.4 km ), and the Gila– Salt River system historically accounted for another 1.7 million acre-feet (2.1 km ). While much of this water was lost to evaporation in the deserts of the Lower Basin, anywhere from 10 to 20 million acre-feet (12 to 25 km ) per year reached
29346-495: The massive Hoover and Glen Canyon Dams, inflows to Lake Powell still experience distinct spring highs and winter lows, though overall volumes have been reduced due to Upper Basin water diversions. Flow regimes in a few Upper Basin tributaries, such as the Yampa River , remain almost completely unaltered. By the 1950s, the Colorado delta was regularly drying up in fall and winter, though spring high flows often still made it to
29547-409: The maximum generating capacity to 1,345 megawatts at the time. Original plans called for 16 large generators, eight on each side of the river, but two smaller generators were installed instead of one large one on the Arizona side for a total of 17. The smaller generators were used to serve smaller communities at a time when the output of each generator was dedicated to a single municipality, before
29748-400: The monument of dedication plaza, a plaque to memorialize the workers killed and the bas-reliefs on the elevator towers. In his words, Hansen wanted his work to express "the immutable calm of intellectual resolution, and the enormous power of trained physical strength, equally enthroned in placid triumph of scientific accomplishment", because "[t]he building of Hoover Dam belongs to the sagas of
29949-473: The most common cause of death on the dam site; the high scalers' work thus helped ensure worker safety. One high scaler was able to save a life in a more direct manner: when a government inspector lost his grip on a safety line and began tumbling down a slope towards almost certain death, a high scaler was able to intercept him and pull him into the air. The construction site had become a magnet for tourists. The high scalers were prime attractions and showed off for
30150-438: The name Hoover Dam was restored by Congress . Since about 1900, the Black Canyon and nearby Boulder Canyon had been investigated for their potential to support a dam that would control floods, provide irrigation water, and produce hydroelectric power . In 1928, Congress authorized the project. The winning bid to build the dam was submitted by a consortium named Six Companies, Inc. , which began construction in early 1931. Such
30351-519: The name. The name was descriptive and was an inside joke among the San Franciscans in the bid, where "Six Companies" was also a Chinese benevolent association in the city . There were three valid bids, and Six Companies' bid of $ 48,890,955 was the lowest, within $ 24,000 of the confidential government estimate of what the dam would cost to build, and five million dollars less than the next-lowest bid. The city of Las Vegas had lobbied hard to be
30552-432: The nation's leading dam builder, Frank Crowe . They formed a joint venture to bid for the project with Pacific Bridge Company of Portland, Oregon ; Henry J. Kaiser & W. A. Bechtel Company of San Francisco; MacDonald & Kahn Ltd. of Los Angeles; and the J.F. Shea Company of Portland, Oregon. The joint venture was called Six Companies, Inc. as Bechtel and Kaiser were considered one company for purposes of Six in
30753-506: The nonnative tamarisk (also known as salt cedar), arrow-weed , and iodine bush , a transformation that has decreased the habitat value of the riparian forest. Full reservoir conditions coupled with a series of flood events throughout the 1980s and early 1990s resulted in flood releases that reached the delta. These flows reestablished an active floodplain and revegetated many areas of the floodplain within irrigation and flood control levels, and helped to reestablish riparian forests. A scheme
30954-688: The north and south, and enabled the expansion of trade to the Pima and Maricopa in the east and coastal California tribes in the west. The Navajo (Diné) began migrating into the Colorado River Basin around 1000-1500 CE, and eventually exercised influence over much of the Colorado Plateau. Originally hunter-gatherers, they acquired knowledge of farming from the Puebloans and adopted a more sedentary lifestyle over time, making extensive use of irrigation in their settlements. The Navajo gradually displaced Hopi settlements as they expanded into northern Arizona after
31155-524: The northernmost part of the gulf in approximately 1 million years. Cut off from the ocean, the portion of the gulf north of the delta eventually evaporated and formed the Salton Sink , which reached about 260 feet (79 m) below sea level. Since then the river has changed course into the Salton Sink at least three times, transforming it into Lake Cahuilla , which at maximum size flooded up
31356-542: The number of black people employed by Six Companies never exceeded thirty, mostly lowest-pay-scale laborers in a segregated crew, who were issued separate water buckets. As part of the contract, Six Companies, Inc. was to build Boulder City to house the workers. The original timetable called for Boulder City to be built before the dam project began, but President Hoover ordered work on the dam to begin in March 1931 rather than in October. The company built bunkhouses, attached to
31557-423: The ocean. After the initial closure of Glen Canyon Dam in 1963, these seasonal flows were almost completely eliminated, with the exception of a few very wet years, such as 1983–1987. In 1984, 16.5 million acre-feet (20.4 km ) of excess runoff reached the ocean. Flows have further declined due to evaporation from reservoirs and, particularly after 2000, reduced snowpack with warming winter temperatures in
31758-440: The penstocks for maintenance. Following an uprating project from 1986 to 1993, the total gross power rating for the plant, including two 2.4 megawatt Pelton turbine -generators that power Hoover Dam's own operations is a maximum capacity of 2080 megawatts. The annual generation of Hoover Dam varies. The maximum net generation was 10.348 TWh in 1984, and the minimum since 1940 was 2.648 TWh in 1956. The average power generated
31959-531: The potential for uneven cooling and contraction of the concrete posed a serious problem. Bureau of Reclamation engineers calculated that if the dam were to be built in a single continuous pour, the concrete would take 125 years to cool, and the resulting stresses would cause the dam to crack and crumble. Instead, the ground where the dam would rise was marked with rectangles, and concrete blocks in columns were poured, some as large as 50 ft square (15 m) and 5 feet (1.5 m) high. Each five-foot form contained
32160-476: The powerhouse was carried out simultaneously with the excavation for the dam foundation and abutments. The excavation of this U-shaped structure located at the downstream toe of the dam was completed in late 1933 with the first concrete placed in November 1933. Filling of Lake Mead began February 1, 1935, even before the last of the concrete was poured that May. The powerhouse was one of the projects uncompleted at
32361-479: The project, together with their families. Another camp, on the flats along the Colorado River, was officially called Williamsville, but was known to its inhabitants as "Ragtown". When construction began, Six Companies hired large numbers of workers, with more than 3,000 on the payroll by 1932 and with employment peaking at 5,251 in July 1934. "Mongolian" (Chinese) labor was prevented by the construction contract, while
32562-565: The proposal, citing doubts about the unproven technique and questions as to whether it would, in fact, save money. In 1922, the Reclamation Service presented a report calling for the development of a dam on the Colorado River for flood control and electric power generation. The report was principally authored by Davis and was called the Fall-Davis report after Interior Secretary Albert Fall . The Fall-Davis report cited use of
32763-462: The railroad had reached Grand Junction, and a spur up the Colorado to Glenwood Springs was completed in 1887. In Arizona and Utah Territories , many early settlers were Mormons fleeing religious persecution in the Midwest. Mormons founded agricultural colonies at Fort Santa Clara in 1855 and St. Thomas , now flooded under Lake Mead, in 1865. Stone's Ferry , crossing the Colorado at the mouth of
32964-402: The region, they became involved in skirmishes with the Mohave, spurring U.S. Army expeditions that culminated in the 1859 Battle of the Colorado River which concluded the Mohave War . In the 1870s the Mohave were moved to the Fort Mohave and Colorado River reservations. Chemehuevi and later some Hopi and Navajo peoples were also moved to the Colorado River reservation, where they today form
33165-445: The remainder were talked into leaving by law enforcement. On August 13, the company began hiring workers again, and two days later, the strike was called off. While the workers received none of their demands, the company guaranteed there would be no further reductions in wages. Living conditions began to improve as the first residents moved into Boulder City in late 1931. A second labor action took place in July 1935, as construction on
33366-404: The remote Pahreah Crossing in Arizona, where he took over a ferry first established in 1864 by Jacob Hamblin . This, the only river crossing for hundreds of miles not hemmed in by vertical canyon walls, became known as Lee's Ferry . While Lee was tried and subsequently executed in 1877, the ferry remained a major transportation link until the Navajo Bridge was completed nearby in 1928, rendering
33567-454: The river that flow through the Grand Canyon are largely encompassed by Grand Canyon National Park and are known for their difficult whitewater, separated by pools that reach up to 110 feet (34 m) in depth. At the lower end of Grand Canyon, the Colorado widens into Lake Mead , the largest reservoir in the continental United States, formed by Hoover Dam on the border of Arizona and Nevada . Situated southeast of metropolitan Las Vegas ,
33768-430: The river's flow reached the delta at that time, its freshwater, silt, and nutrients helped create and sustain a complex system of estuarial wetlands that provided feeding and nesting grounds for birds, and spawning habitat for fish and marine mammals. In contrast to the surrounding Sonoran Desert , the Colorado River delta's abundance was striking. Early explorers reported jaguars , beavers , deer , and coyotes in
33969-401: The river's present course and the Grand Canyon were formed is uncertain. Before the Gulf of California was formed around 12 to 5 million years ago by faulting processes along the boundary of the North American and Pacific plates, the Colorado flowed west to an outlet on the Pacific Ocean—possibly Monterey Bay on the Central California coast, and may have played a role in the formation of
34170-528: The river's suitability as a navigation route, Ives remarked: "Ours has been the first, and will doubtless be the last, party of whites to visit this profitless locality. It seems intended by nature that the Colorado River, along the greater portion of its lonely and majestic way, shall be forever unvisited and undisturbed." The last part of the Colorado River to be surveyed was the Grand Canyon itself. In 1869, John Wesley Powell with nine men set out on an expedition from Green River Station, Wyoming . They were
34371-512: The river, starting in 1852 with the sidewheeler Uncle Sam , whose first voyage from the Gulf to Yuma took fifteen days. Exploration by steamboat soon advanced upriver. In 1857, George A. Johnson in the General Jesup was able to reach Pyramid Canyon , over 300 miles (480 km) north of Fort Yuma. He was followed by Lt. Joseph Christmas Ives who used a specially built shallow-draft steamboat, Explorer , to reach Black Canyon , where Hoover Dam stands today. Having set out to determine
34572-413: The same year Melchior Díaz explored the Colorado River's delta and named it Rio del Tizon ("fire brand river"), after seeing a practice used by the local people for warming themselves. By the late 1500s or early 1600s, the Utes had acquired horses from the Spanish, and their use for hunting, trade and warfare soon became widespread among Utes and Navajo in the Colorado River basin. This conferred them
34773-454: The seventh largest drainage basin in North America. About 238,600 square miles (618,000 km ), or 97 percent of the basin, is in the United States. The basin extends into western Colorado and New Mexico, southwestern Wyoming , eastern and southern Utah, southeastern Nevada and California, and most of Arizona. The areas drained within Baja California and Sonora in Mexico are very small and do not contribute significant runoff. Aside from
34974-435: The side-walls were also excavated to reach virgin rock, as weathered rock might provide pathways for water seepage. Shovels for the excavation came from the Marion Power Shovel Company . The men who removed this rock were called "high scalers". While suspended from the top of the canyon with ropes, the high-scalers climbed down the canyon walls and removed the loose rock with jackhammers and dynamite . Falling objects were
35175-399: The site for a dam. Service chief Arthur Powell Davis proposed using dynamite to collapse the walls of Boulder Canyon, 20 miles (32 km) north of the eventual dam site, into the river. The river would carry off the smaller pieces of debris, and a dam would be built incorporating the remaining rubble. In 1922, after considering it for several years, the Reclamation Service finally rejected
35376-440: The site is located submits a nomination. Once designated, Biosphere Reserves remain under the sovereign jurisdiction of the countries where they are located. Federal Mexican governmental agencies with administrative authority over the Biosphere Reserve include the National Commission of Protected Natural Areas ( CONANP ) and the Secretary of the Environment, Natural Resources and Fisheries ( SEMARNAP ). In addition to designation as
35577-443: The site is located. Colorado River The Colorado River ( Spanish : Río Colorado ) is one of the principal rivers (along with the Rio Grande ) in the Southwestern United States and in northern Mexico . The 1,450-mile-long (2,330 km) river, the 5th longest in the United States , drains an expansive, arid watershed that encompasses parts of seven U.S. states and two Mexican states. The name Colorado derives from
35778-477: The situation. It found that the work had been incompletely done, and was based on less than a full understanding of the canyon's geology. New holes were drilled from inspection galleries inside the dam into the surrounding bedrock. It took nine years (1938–47) under relative secrecy to complete the supplemental grout curtain. The first concrete was poured into the dam on June 6, 1933, 18 months ahead of schedule. Since concrete heats and contracts as it cures,
35979-442: The supervising architect to the Bureau of Reclamation, was brought in to redesign the exteriors. Kaufmann greatly streamlined the design and applied an elegant Art Deco style to the entire project. He designed sculpted turrets rising seamlessly from the dam face and clock faces on the intake towers set for the time in Nevada and Arizona—both states are in different time zones, but since Arizona does not observe daylight saving time ,
36180-481: The system's capacity for use and storage. The loss of freshwater flows to the delta over the twentieth century has reduced delta wetlands to about 5 percent of their original extent, and non-native species have compromised the ecological health of much of what remains. Stress on ecosystems has allowed invasive plants to out-compete native species along Colorado River riparian areas. Native forests of cottonwood and willow have yielded to sand and mudflats dominated by
36381-440: The tidal bore—locally called El Burro —formed in the estuary about Montague Island in Baja California and propagated upstream. The Colorado is joined by over 25 significant tributaries, of which the Green River is the largest by both length and discharge. The Green River takes drainage from the Wind River Range of west-central Wyoming, from Utah's Uinta Mountains , and from the Rockies of northwestern Colorado. The Gila River
36582-409: The time , the limit of transmission of electric power was 80 miles (130 km), and there were few customers (mostly mines) within that limit. Edison allowed land options it held on the river to lapse—including an option for what became the site of Hoover Dam. In the following years, the Bureau of Reclamation (BOR), known as the Reclamation Service at the time, also considered the Lower Colorado as
36783-418: The time of the formal dedication on September 30, 1935; a crew of 500 men remained to finish it and other structures. To make the powerhouse roof bombproof, it was constructed of layers of concrete, rock, and steel with a total thickness of about 3.5 feet (1.1 m), topped with layers of sand and tar. In the latter half of 1936, water levels in Lake Mead were high enough to permit power generation, and
36984-515: The tip of the Gulf of California between Baja California and Sonora . Known for its dramatic canyons, whitewater rapids, and eleven U.S. National Parks , 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
37185-447: The tunnels for maintenance. To protect the construction site from the Colorado River and to facilitate the river's diversion, two cofferdams were constructed. Work on the upper cofferdam began in September 1932, even though the river had not yet been diverted. The cofferdams were designed to protect against the possibility of the river's flooding a site at which two thousand men might be at work, and their specifications were covered in
37386-451: The tunnels with concrete. First the base, or invert, was poured. Gantry cranes , running on rails through the entire length of each tunnel were used to place the concrete. The sidewalls were poured next. Movable sections of steel forms were used for the sidewalls. Finally, using pneumatic guns, the overheads were filled in. The concrete lining is 3 feet (1 m) thick, reducing the finished tunnel diameter to 50 ft (15 m). The river
37587-422: The tunnels with large concrete plugs. The downstream halves of the tunnels following the inner plugs are now the main bodies of the spillway tunnels. The inner diversion tunnels were plugged at approximately one-third of their length, beyond which they now carry steel pipes connecting the intake towers to the power plant and outlet works. The inner tunnels' outlets are equipped with gates that can be closed to drain
37788-480: The upper Colorado River basin. 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. Numerous water projects have also involved state and local governments. With all of their waters fully allocated, both
37989-423: The valley to present-day Indio, California . The lake took about 50 years to evaporate after the Colorado resumed flowing to the Gulf. The present-day Salton Sea can be considered the most recent incarnation of Lake Cahuilla, though on a much smaller scale. Between 1.8 million and 10,000 years ago, massive flows of basalt from the Uinkaret volcanic field in northern Arizona dammed the Colorado River within
38190-615: The watchers. The high scalers received considerable media attention, with one worker dubbed the "Human Pendulum" for swinging co-workers (and, at other times, cases of dynamite) across the canyon. To protect themselves against falling objects, some high scalers dipped cloth hats in tar and allowed them to harden. When workers wearing such headgear were struck hard enough to inflict broken jaws, they sustained no skull damage. Six Companies ordered thousands of what initially were called "hard boiled hats" (later " hard hats ") and strongly encouraged their use. The cleared, underlying rock foundation of
38391-471: The waterway was stabilized, it proved unsatisfactory because of constant disputes with landowners on the Mexican side of the border. As the technology of electric power transmission improved, the Lower Colorado was considered for its hydroelectric -power potential. In 1902, the Edison Electric Company of Los Angeles surveyed the river in the hope of building a 40-foot (12 m) rock dam which could generate 10,000 horsepower (7,500 kW). However, at
38592-509: The waves better, and we shall have little to carry when we make a portage. We are three-quarters of a mile in the depths of the earth, and the great river shrinks into insignificance, as it dashes its angry waves against the walls and cliffs, that rise to the world above; they are but puny ripples, and we but pigmies, running up and down the sands, or lost among the boulders. We have an unknown distance yet to run; an unknown river yet to explore. What falls there are, we know not; what rocks beset
38793-432: Was 4.2 TWh/year for 1947–2008. In 2015, the dam generated 3.6 TWh. The amount of electricity generated by Hoover Dam has been decreasing along with the falling water level in Lake Mead due to the prolonged drought since year 2000 and high demand for the Colorado River's water. By 2014 its generating capacity was downrated by 23% to 1592 MW and was providing power only during periods of peak demand. Lake Mead fell to
38994-484: Was a peninsula, not an island as previously believed. In the 1700s and early 1800s many Spanish and American explorers believed in the existence of a Buenaventura River that ran from the Rocky Mountains to the Pacific coast. In 1776, Silvestre Vélez de Escalante attached this name to the upper Green River, and a number of later maps showed this connecting to Lake Timpanogos (now Utah Lake ) and flowing west to California. The Dominguez–Escalante expedition first reached
39195-418: Was a visitor to the site; the remainder were employees of various contractors not part of Six Companies. Ninety-six of the deaths occurred during construction at the site. Not included in the official number of fatalities were deaths that were recorded as pneumonia . Workers alleged that this diagnosis was a cover for death from carbon monoxide poisoning (brought on by the use of gasoline-fueled vehicles in
39396-446: Was awarded two patents for their design. These buckets, which weighed 20 short tons (18.1 t; 17.9 long tons) when full, were filled at two massive concrete plants on the Nevada side, and were delivered to the site in special railcars . The buckets were then suspended from aerial cableways which were used to deliver the bucket to a specific column. As the required grade of aggregate in the concrete differed depending on placement in
39597-428: Was diverted into the two Arizona tunnels on November 13, 1932; the Nevada tunnels were kept in reserve for high water. This was done by exploding a temporary cofferdam protecting the Arizona tunnels while at the same time dumping rubble into the river until its natural course was blocked. Following the completion of the dam, the entrances to the two outer diversion tunnels were sealed at the opening and halfway through
39798-434: Was inhabited for thousands of years by numerous tribes of the Patayan cultures, many of which belong to the Yuman-Cochimi language group . These include the Walapai , Havasupai and Yavapai in the Grand Canyon region; the Mohave , Halchidhoma , Quechan , and Halyikwamai along the Colorado River between Black Canyon and the Mexican border, and the Cocopah around the Colorado River Delta. The Chemehuevi (a branch of
39999-422: Was necessary to remove accumulated erosion soils and other loose materials in the riverbed until sound bedrock was reached. Work on the foundation excavations was completed in June 1933. During this excavation, approximately 1,500,000 cu yd (1,100,000 m ) of material was removed. Since the dam was an arch-gravity type, the side-walls of the canyon would bear the force of the impounded lake. Therefore,
40200-400: Was no space for a construction camp at the bottom of the canyon or for a spillway. The Service investigated Black Canyon and found it ideal; a railway could be laid from the railhead in Las Vegas to the top of the dam site. Despite the site change, the dam project was referred to as the "Boulder Canyon Project". With little guidance on water allocation from the Supreme Court , proponents of
40401-445: Was to accompany each bid; the winner would have to post a $ 5 million performance bond . The contractor had seven years to build the dam, or penalties would ensue. The Wattis Brothers , heads of the Utah Construction Company , were interested in bidding on the project, but lacked the money for the performance bond. They lacked sufficient resources even in combination with their longtime partners, Morrison-Knudsen , which employed
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