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130-406: During the late 19th century, the valley was renowned for its natural beauty – often compared to that of Yosemite Valley – but also targeted for the development of water supply for irrigation and municipal interests. The controversy over damming Hetch Hetchy became mired in the political issues of the day. The law authorizing the dam passed Congress on December 7, 1913. In 1923, the O'Shaughnessy Dam

260-477: A "recreational value" of up to $ 178 million per year, or possibly an overall economic value of up to $ 100 billion. Those in opposition of dam removal state that demolishing O'Shaughnessy Dam would take away a valuable source of clean, renewable hydroelectric power in the Kirkwood and Moccasin powerhouses; even if measures such as seasonal water diversion into the powerhouses were employed, it would only make up for

390-528: A "small but noisy" waterfall and natural pool existed on the Tuolumne River marked the upper entrance to Hetch Hetchy Valley, informally known as Tuolumne Fall (not to be confused with a similarly named waterfall several miles upriver near Tuolumne Meadows ). The waterfall on the Tuolumne is now submerged under Hetch Hetchy Reservoir. The Hetch Hetchy Valley began as a V-shaped river canyon cut out by

520-614: A Miwok word earlier anglicized as hatchhatchie , which means "edible grasses" or "magpie". It is likely that the edible grass was blue dicks . Chief Tenaya of the Yosemite Valley's Ahwaneechee tribe claimed that Hetch Hetchy was Miwok for "Valley of the Two Trees", referring to a pair of yellow pines that once stood at the head of Hetch Hetchy. Miwok names are still used for features, including Tueeulala Fall, Wapama Fall, and Kolana Rock. While its cousin Yosemite Valley to

650-745: A New Moccasin Powerhouse in 1969 when the Old Moccasin Powerhouse was taken out of service. Finally, in 1988, a third generator was added to the Kirkwood Powerhouse. Hetch Hetchy Valley serves as the primary water source for the City and County of San Francisco and several surrounding municipalities in the greater San Francisco Bay Area . The dam and reservoir, combined with a series of aqueducts, tunnels, and hydroelectric plants as well as eight other storage dams, comprise

780-518: A bill on June 30, 1864, granting Yosemite Valley and the Mariposa Grove of giant sequoias to the State of California "for public use, resort and recreation," the two tracts "shall be inalienable for all time". This was the first time in history that a federal government had set aside scenic lands simply to protect them and to allow for their enjoyment by all people. Simply designating an area

910-536: A couple of months, often as entire families with many possessions. Early hotels were therefore set up for extended stays and catered primarily to wealthy patrons who could spend extended periods away from home. One of these hotels—the Wawona Hotel , built in the 1880s—still operates. After the Valley became a park, the surrounding territory was still subject to logging, mining, and grazing. John Muir publicized

1040-609: A fraction of the original power production. The remaining deficit would likely have to be replaced by polluting fossil fuel generation. The removal of the dam would be extremely costly, at least $ 3–10 billion, and the transport of the demolished material away from the dam site along the narrow, winding Hetch Hetchy Road would be a logistical nightmare with possible environmental impacts. Most importantly, San Francisco would lose its source of high-quality mountain water, and would have to depend on lower-quality water from other reservoirs – which would require costly filtration and re-engineering of

1170-557: A major earthquake and subsequent fire that devastated San Francisco, the inadequacy of the city's water system was made tragically clear. San Francisco applied to the United States Department of the Interior to gain water rights to Hetch Hetchy, and in 1908 President Theodore Roosevelt's Secretary of the Interior, James R. Garfield , granted San Francisco the rights to development of the Tuolumne River. This provoked

1300-786: A man's blue shirt and turn it brown, and were voracious as mosquitoes would be." People have lived in Hetch Hetchy Valley for over 6,000 years. Native American cultures were prominent before the 1850s when the first settlers from the United States arrived in the Sierra Nevada. During summer, people of the Miwok and Paiute came to Hetch Hetchy from the Central Valley in the west and the Great Basin in

1430-434: A maximum depth of over 3,000 ft (910 m); the length of the valley was 3 mi (4.8 km) with a width ranging from 1 ⁄ 8 to 1 ⁄ 2 mile (660 to 2,640 ft; 200 to 800 m). The valley floor consisted of roughly 1,200 acres (490 ha) of meadows fringed by pine forest, through which meandered the Tuolumne River and numerous tributary streams. Kolana Rock , at 5,772 ft (1,759 m),

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1560-436: A new 300-car parking lot. The plan will allow the valley to accommodate a peak of 20,100 visitors per day. The plan has been criticized for prioritizing park visitors over the preservation of the river and the valley. Some believe there should be further limitations to the number of cars and parking lots in the valley, and more focus on public transportation. On busy summer days, there can be long delays and traffic gridlock at

1690-584: A paper in Journal of Natural History in 2012, reporting that: "This microhabitat, as well as interstitial spaces between scree blocks elsewhere on this slope, supports an important assemblage of boreal and arctic bryophytes , pteridophytes , and arthropods that are disjunct from their normal ranges far to the north. This freezing scree slope represents a classic example of a palaeo refugium that significantly contributes to [the] protection and maintenance of regional landscape biodiversity ." Ice Mountain ,

1820-494: A park isn't sufficient to protect it. California did not set up an administration for the park until 1866 when the state appointed Galen Clark as the park's guardian. An 11-year struggle followed to resolve homesteading claims in the valley. The challenge of increasing tourism, with the need to first build stagecoach roads, then the Yosemite Valley Railroad , along with hotels and other facilities in and around

1950-494: A private power company, Pacific Gas & Electric (PG&E). San Francisco was able to accomplish this in 1925 by claiming it had run out of funds to extend the Hetch Hetchy transmission line all the way to the city. The terminus of the incomplete line was "conveniently located next to a PG&E substation", which connected to PG&E's private line which in turn bridged the gap to San Francisco. The city justified this as

2080-400: A reservoir", with pristine water, lack of development or private property, a steep-sided and flat-floored profile that would maximize the amount of water stored, and a narrow outlet ideal for placement of a dam. They claimed the valley was not unique and would be even more beautiful with a lake. Muir predicted that this lake would create an unsightly "bathtub ring" around its perimeter, caused by

2210-458: A result, the rivers feeding Hetch Hetchy Reservoir have extremely low loads of sediments and nutrients. The watershed is also strictly protected, so swimming and boating are prohibited at the reservoir (although fishing is permitted at the reservoir and in the rivers which feed it), a measure which is considered unusual for US lakes outside the region. In 2018, the Department of the Interior of

2340-452: A roughly east–west direction, with an average width of about 1 mile (1.6 km). Yosemite Valley represents only one percent of the park area, but it is where most visitors arrive and stay. More than half a dozen creeks tumble from hanging valleys at the top of granite cliffs that can rise 3,000–3,500 feet (910–1,070 m) above the valley floor, which itself is 4,000 ft (1,200 m) above sea level . These streams combine into

2470-404: A seven-year environmental struggle with the environmental group Sierra Club , led by John Muir . Muir observed: Dam Hetch Hetchy! As well dam for water-tanks the people's cathedrals and churches, for no holier temple has ever been consecrated by the heart of man. Proponents of the dam replied that out of multiple sites considered by San Francisco, Hetch Hetchy had the "perfect architecture for

2600-494: A shift to using smaller rock points, indicating development and use of the bow and arrow ; and the "Mariposa" phase, from 1200 until European contact in the mid-19th century. In the 19th century, it was inhabited by a Miwok band who called the Valley "Ah-wah-nee" and themselves the Ahwahnechee . This group had trading and family ties to Mono Lake Paiutes from the eastern side of the Sierra Nevada. They annually burned

2730-412: A significant part of this natural community include: Yosemite National Park had a record number of 5 million visitors in 2016. In 2020 visitation dropped to 2,268,313 visitors. A reservation system was implemented in 2020, which required a reservation in order to enter the park. The reservation system has been periodically lifted and reimplemented since 2021. On July 24, 2018, several areas of

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2860-730: A system known as the Hetch Hetchy Project , which provides 80% of the water supply for 2.6 million people. The project is operated by the San Francisco Public Utilities Commission . The city must pay a lease of $ 30,000 per year for the use of Hetch Hetchy, which sits on federal land. The aqueduct delivers an average of 265,000 acre⋅ft (327,000,000 m) of water each year, or 31,900,000 cu ft (900,000 m) per day, to residents of San Francisco and San Mateo , Santa Clara and Alameda Counties. As completed, O'Shaughnessy Dam

2990-481: A temporary measure, but no attempt to follow through with completing the municipal grid was ever made. Peter Byrne of SF Weekly has stated that "the plain language of the Raker Act itself and experts who are familiar with the act (and have no stake in city politics) all agree: The city of San Francisco is not in violation of the Raker Act." Harold L. Ickes , Secretary of the Interior in the late 1930s, said there

3120-777: Is 910 feet (280 m) long, spanning the valley at its narrow outlet. The dam contains 675,000 cu yd (516,000 m) of concrete. The Hetch Hetchy Reservoir created by the dam has a capacity of 360,400 acre⋅ft (0.4445 km), with a maximum area of 1,972 acres (798 ha) and a maximum depth of 306 feet (93 m). From Hetch Hetchy Reservoir, the water flows through the Canyon and Mountain Tunnels to Kirkwood and Moccasin Powerhouses , which have capacities of 124 and 110 megawatts , respectively. An additional hydroelectric system comprising Cherry Lake , Lake Eleanor and

3250-665: Is a glacial valley in Yosemite National Park in the western Sierra Nevada mountains of Central California , United States. The valley is about 7.5 mi (12.1 km) long and 3,000–3,500 ft (910–1,070 m) deep, surrounded by high granite summits such as Half Dome and El Capitan , and densely forested with pines . The valley is drained by the Merced River , and a multitude of streams and waterfalls flow into it, including Tenaya , Illilouette, Yosemite and Bridalveil Creeks . Yosemite Falls

3380-443: Is a massive rock spire on the south side of the Hetch Hetchy Valley. Hetch Hetchy Dome , at 6,197 ft (1,889 m), lies directly north of it. The locations of these two formations roughly correspond with those of Cathedral Rocks and El Capitan seen from Tunnel View in Yosemite Valley. A broad, low rocky outcrop situated between Kolana Rock and Hetch Hetchy Dome divided the former meadow in two distinct sections. The valley

3510-501: Is fed by the Tuolumne River , Falls Creek , Tiltill Creek , Rancheria Creek , and numerous smaller streams which collectively drain a watershed of 459 sq mi (1,190 km). In its natural state, the valley floor was marshy and often flooded in the spring when snow melt in the high Sierra cascaded down the Tuolumne River and backed up behind the narrow gorge which is now spanned by O'Shaughnessy Dam. The entire valley

3640-419: Is formed by rockfall, which distinguishes it from colluvium . Colluvium is rock fragments or soil deposited by rainwash , sheetwash , or slow downhill creep , usually at the base of gentle slopes or hillsides. However, the terms scree , talus , and sometimes colluvium tend to be used interchangeably. The term talus deposit is sometimes used to distinguish the landform from the material of which it

3770-455: Is generally good sorting of sediment by size: larger particles accumulate more rapidly at the bottom of the slope. Cementation occurs as fine-grained material fills in gaps between debris. The speed of consolidation depends on the composition of the slope; clayey components will bind debris together faster than sandy ones. Should weathering outpace the supply of sediment, plants may take root. Plant roots diminish cohesive forces between

3900-403: Is left to take hold in the valley, eventually a forest would grow, rather than the meadow being restored. However, the same NPS study also finds that with intensive management, an outcome in which "the entire valley would appear much as it did before construction of the reservoir" is feasible. The dam would not have to be completely removed; rather, it would only be necessary to cut a hole through

4030-544: Is listed as a National Historic District and as a California Historical Landmark . After the creation of the Park Service, many separate hotel owners held separate concession contracts. The Yosemite Park Company had built the Yosemite Lodge and Yosemite Village had its own group of merchants. Fire had destroyed a number of the original valley hotels and concession owners came and went until Park Service forced

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4160-415: Is loosely synonymous with talus , material that accumulates at the base of a projecting mass of rock, or talus slope , a landform composed of talus. The term scree is sometimes used more broadly for any sheet of loose rock fragments mantling a slope, while talus is used more narrowly for material that accumulates at the base of a cliff or other rocky slope from which it has obviously eroded. Scree

4290-455: Is made. The exact definition of scree in the primary literature is somewhat relaxed, and it often overlaps with both talus and colluvium . The term scree comes from the Old Norse term for landslide , skriða , while the term talus is a French word meaning a slope or embankment. Talus deposits typically have a concave upwards form, where the maximum inclination corresponds to

4420-469: Is near Yosemite's western boundary, but the long, narrow, fingerlike reservoir stretches eastward for about 8 miles (13 km). Wapama Falls , at 1,080 ft (330 m), and Tueeulala Falls , at 840 ft (260 m) – both among the tallest waterfalls in North America – are both located in Hetch Hetchy Valley. Rancheria Falls is located farther southeast, on Rancheria Creek. Formerly,

4550-541: Is now flooded under an average 300 ft (91 m) of water behind the dam, although it occasionally reemerges in droughts, as it did in 1955, 1977, and 1991. Upstream from the valley lies the Grand Canyon of the Tuolumne , while the smaller Poopenaut Valley is directly downstream from O'Shaughnessy Dam. The Hetch Hetchy Road drops into the valley at the dam, but all points east of there are roadless, and accessible only to hikers and equestrians. The O'Shaughnessy Dam

4680-508: Is still a possibility of the deposit slopes themselves failing. If the talus deposit pile shifts and the particles exceed the angle of repose, the scree itself may slide and fail. Phenomena such as acid rain may also contribute to the chemical degradation of rocks and produce more loose sediments. Biotic processes often intersect with both physical and chemical weathering regimes, as the organisms that interact with rocks can mechanically or chemically alter them. Lichen frequently grow on

4810-411: Is the thermal conductivity of the debris material, T s is the ambient temperature above the debris surface, T i is the temperature at the lower surface of the debris, and d is the thickness of the debris layer. Debris with a low thermal conductivity value, or a high thermal resistivity , will not efficiently transfer energy through to the glacier, meaning the amount of heat energy reaching

4940-417: Is the highest waterfall in North America and is a big attraction, especially in the spring, when the water flow is at its peak. The valley is renowned for its natural environment and is regarded as the centerpiece of Yosemite National Park . The valley is the main attraction in the park for the majority of visitors and a bustling hub of activity during tourist season in the summer months. Most visitors enter

5070-450: Is thought to be most common during the spring and fall, when the daily temperatures fluctuate around the freezing point of water, and snow melt produces ample free water. The efficiency of freeze-thaw processes in scree production is a subject of ongoing debate. Many researchers believe that ice formation in large open fracture systems cannot generate high enough pressures to force the fracturing apart of parent rocks, and instead suggest that

5200-661: The California Gold Rush . Miners did not stay in the area for long, however, as richer deposits occurred further south along the Merced River and in the Big Oak Flat area. After the valley's native inhabitants were driven out by the newcomers, it was used by ranchers, many of whom were former miners, to graze livestock. Animals were principally driven along Joseph Screech's trail from Big Oak Flat to Hetch Hetchy. Its meadows provided abundant feed for "thousands of head of sheep and cattle that entered lean and lank in

5330-758: The Hayward fault . Pipelines 1 and 2 cross the San Francisco Bay to the south of the Dumbarton Bridge , while pipelines 3 and 4 run to the south of the bay. In the Bay Area, Hetch Hetchy water is stored in local facilities including Calaveras Reservoir , Crystal Springs Reservoir , and San Antonio Reservoir . Pipelines 3 and 4 end at the Pulgas Water Temple , a small park that contains classical architectural elements which celebrate

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5460-467: The Merced River , which flows out from the western end of the valley, down the rest of its canyon to the San Joaquin Valley . The flat floor of Yosemite Valley holds both forest and large open meadows , which have views of the surrounding crests and waterfalls . Below is a description of these features, looking first at the walls above, moving west to east as a visitor does when entering

5590-740: The Pinchot-Ballinger Controversy caused both Richard A. Ballinger and Gifford Pinchot to resign and be fired respectively. The openings in the Taft administration led to the eventual success of the Raker Act. Work on the Hetch Hetchy Project began in 1914. The 68 mi (109 km) Hetch Hetchy Railroad was constructed to link the Sierra Railway with Hetch Hetchy Valley, allowing for direct rail shipment of construction materials from San Francisco to

5720-537: The Yosemite Firefall . This "fall" was large batches of red hot embers dropped from Glacier Point. The Park Service stopped this practice in 1969 as part of their long process of de-emphasizing artificial park attractions. On July 6, 1996, a massive rock slide , weighing an estimated 60,000–80,000 tons, crashed 1,800 feet (550 m) into the valley from the east side of Glacier Point, traveling at over 160 mph (260 km/h). Dust blanketed that part of

5850-406: The angle of repose of the mean debris particle size. Scree slopes are often assumed to be close to the angle of repose. This is the slope at which a pile of granular material becomes mechanically unstable. However, careful examination of scree slopes shows that only those that are either rapidly accumulating new material, or are experiencing rapid removal of material from their bases, are close to

5980-399: The mayor of San Francisco at the time, said in a Los Angeles Times story in 1987: "All this is for an expanded campground? ... It's dumb, dumb, dumb." Hodel, now retired, remains a strong proponent of restoring Hetch Hetchy Valley and Senator Feinstein remained strongly against restoration. The George W. Bush administration proposed allocating $ 7 million to studying the removal of

6110-529: The 1833 Joseph Walker Party, which was the first to cross the Sierra Nevada from east to west. The first descriptions of Yosemite, however, came nearly 20 years later. The 1849 California Gold Rush led to conflicts between miners and Native Americans, and the state formed the volunteer Mariposa Battalion as a punitive expedition against the Native Americans living in the Yosemite area. In 1851,

6240-413: The 1880s, San Francisco was looking to Hetch Hetchy water as a fix for its outdated and unreliable water system. The city would repeatedly try to acquire water rights to Hetch Hetchy, including in 1901, 1903 and 1905, but was continually rebuffed because of conflicts with irrigation districts that had senior water rights on the Tuolumne River, and because of the valley's national park status. In 1906, after

6370-399: The 19th century, the first white visitors to the valley did not realize that Hetch Hetchy's extensive meadows were the product of millennia of management by Native Americans; instead they believed "the valley was purely a product of ancient geological forces (or divine intervention) ... this was fundamental to its allure as a destination and subject." The valley's name may be derived from

6500-881: The Battalion was led by Major Jim Savage , whose trading post on the Merced River the Awaneechee had raided. This and other missions (the Mariposa Wars ) resulted in Chief Teneiya and the Awaneechee spending months on a reservation in the San Joaquin Valley. The band returned the next year to the Valley but took refuge among the Mono Paiutes after further conflicts with miners. Most of the Awaneechee (along with Teneiya) were chased back to

6630-501: The Bay Area, it passes through the Irvington tunnel near the city of Fremont , and the aqueduct splits into four pipelines at 37°32′53″N 121°55′55″W  /  37.548104°N 121.932041°W  / 37.548104; -121.932041 . These are called Bay Division Pipelines (BDPL) 1, 2, 3, and 4, with nominal pipeline diameters of 60, 66, 78, and 96 inches (1.5, 1.7, 2.0 and 2.4 m, respectively). All four pipelines cross

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6760-421: The Hetch Hetchy Valley. Bierstadt described the valley as "smaller than the more famous valley ... but it presents many of the same features in his scenery and is quite as beautiful." When Yosemite Valley became part of a state park in 1864, Hetch Hetchy received no such designation. As the grazing of livestock damaged native plants in the Hetch Hetchy Valley, mountaineer and naturalist John Muir pressed for

6890-472: The Hetch Hetchy area, including the largest North American bat, the western mastiff . Before damming, the valley floor contained abundant stands of black oaks, live oak , Ponderosa pine , Douglas fir , and silver fir bordering the meadows, with alder , willow , poplar and dogwood in the riparian zone along the Tuolumne River. The valley's abundant plants provided nourishment for mule deer , black bears and bighorn sheep . Due to large cataracts on

7020-557: The Holm Powerhouse is also part of the Hetch Hetchy Project, adding another 169 megawatts of generating capacity. The entire system produces about 1.7 billion kilowatt hours per year, enough to meet 20% of San Francisco's electricity needs. After passing through the powerhouses, Hetch Hetchy water flows into the 167 mi (269 km) Hetch Hetchy Aqueduct which travels across the Central Valley. Just before reaching

7150-411: The Kirkwood and Moccasin Powerhouses using lower-impact diversion dams , providing power generation on a seasonal basis, and the increased height, and thus hydraulic head , at Don Pedro would also increase power generation there. Furthermore, the removal of O'Shaughnessy Dam would not require costly sediment control measures, as would be typical on most dam removal projects, because of the high quality of

7280-539: The Merced River take drainage from the Sierra crest and combine at Merced Lake. The Merced then flows down to the end of its canyon ( Little Yosemite Valley ), where it begins what is often called the Giant Staircase . The first drop is Nevada Fall , which drops 594 feet (181 m), bouncing off the granite slope below it. Below is Vernal Fall , 317 feet (97 m) high, one of the most picturesque waterfalls in

7410-551: The Merced River. The following falls tumble from the Valley rim to join it at various points: The features in Yosemite Valley are made of granitic rock emplaced as plutons miles deep during the late Cretaceous . Over time the Sierra Nevada was uplifted, exposing this rock to erosion at the surface. The oldest of these granitic rocks, at 114 million years, occur along the Merced River Gorge west of

7540-617: The Trump administration began to consider a proposal to allow limited boating on the Hetch Hetchy Reservoir for the first time, supported by the advocacy group Restore Hetch Hetchy which argued that "San Francisco received [Hetch Hetchy's] benefits long ago, but the American people have not." The battle over Hetch Hetchy Valley continues today between those who wish to retain the dam and reservoir, and those who wish to drain

7670-433: The Tuolumne River upstream, Hetch Hetchy Valley may have been in the uppermost range for native rainbow trout in the river. Due to its abundant wetlands and stream pools, Hetch Hetchy was notorious among early travelers for becoming infested with mosquitoes in the summertime. Said San Francisco resident William Denman in 1918, "The first time I went into the Hetch Hetchy the mosquitoes were intolerable. They would light upon

7800-479: The Tuolumne River water – in the first 90 years since its construction, only around 2 in (5.1 cm) of sediment had been deposited in Hetch Hetchy Reservoir, much less than most other dams. A 2019 study commissioned by Restore Hetch Hetchy argued that draining the reservoir and equipping the valley with a tourism infrastructure comparable to that of Yosemite Valley (which receives around 100 times as many visitors annually as Hetch Hetchy's 44,000) could result in

7930-538: The Valley and killed by the Paiutes after violating hospitality by stealing horses. While the members of that first expedition of the Mariposa Battalion had heard rumors of what could be found up the Merced River, none were prepared for what they saw March 27, 1851, from what is now called Old Inspiration Point (close to the better-visited Tunnel View). Dr. Lafayette Bunnell later wrote: The grandeur of

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8060-477: The Valley has been curving gently to the left (north). Now a grand curve back to the right begins, with Yosemite Falls on the north, followed by the Royal Arches, topped by North Dome . Opposite, to the south, is Glacier Point , 3,200 feet (980 m) above the Valley floor. At this point the Valley splits in two, one section slanting northeast, with the other curving from south to southeast. Between them, at

8190-400: The Valley was met during the rest of the 19th century. But much environmental damage was caused to the valley itself at that time. The problems that Yosemite Park had under state control was one of the factors in establishing Yellowstone National Park as the first completely national park in 1872. Due to the difficulty of traveling there, early visitors to the valley came for several weeks to

8320-480: The Valley. Ayres' highly detailed angularly exaggerated artwork and his written accounts were distributed nationally and an art exhibition of his drawings was held in New York City. Two of Hutchings' first group of tourists, Milton and Houston Mann, built the first toll route into the valley, with the development of the first hotels in the area and other trails quickly following. Many of the early pioneers in

8450-497: The Valley. The Merced then descends rapids to meet Illilouette Creek, which drops from the valley rim to form Illilouette Fall . They combine at the base of the gorges that contain each stream, and then flow around the Happy Isles to meet Tenaya Creek at the eastern end of Yosemite Valley proper. Tenaya Creek flows southwest from Tenaya Lake and down Tenaya Canyon, finally flowing between Half Dome and North Dome before joining

8580-511: The ancestral Tuolumne River. About one million years ago, the extensive Sherwin glaciation widened, deepened and straightened river valleys along the western slope of the Sierra Nevada, including Hetch Hetchy, Yosemite Valley, and Kings Canyon farther to the south. During the last glacial period , the Tioga Glacier formed from extensive icefields in the upper Tuolumne River watershed; between 110,000 and 10,000 years ago Hetch Hetchy Valley

8710-447: The angle of repose. Most scree slopes are less steep, and they often show a concave shape, so that the foot of the slope is less steep than the top of the slope. Scree with large, boulder-sized rock fragments may form talus caves , or human-sized passages formed in-between boulders. The formation of scree and talus deposits is the result of physical and chemical weathering acting on a rock face, and erosive processes transporting

8840-496: The aqueduct system – to meet its needs. The economic wisdom of removing the dam has been frequently questioned. Some observers, such as Carl Pope (director of the Sierra Club ), stated that Hodel had political motives in proposing the study. The imputed motive was to divide the environmental movement: to see residents of the strongly Democratic city of San Francisco coming out against an environmental issue. Dianne Feinstein ,

8970-653: The arrival of the first Hetch Hetchy water in the city. The Early Intake (Lower Cherry) Powerhouse began commercial operation five years before the O'Shaughnessy Dam was completed. The first Moccasin Powerhouse in Moccasin, California began commercial operation in 1925 followed by the Holm Powerhouse in 1960 (the same month the Early Intake Powerhouse was taken out of service). In 1967 the Robert C. Kirkwood Powerhouse started commercial operation followed by

9100-509: The base in order to drain the water and restore natural flows of the Tuolumne River. Most of the dam would remain in place, both to avoid the enormous costs of demolition and removal, and to serve as a monument for the workers who built it. The water storage provided at Hetch Hetchy could be transferred into Lake Don Pedro lower on the Tuolumne River by raising the New Don Pedro Dam 30 ft (9.1 m). Water could be diverted into

9230-448: The bedrock valley floor, and much smaller Wisconsinian glaciers deposited glacial debris. The biological community on the floor of Yosemite Valley is a diverse one, with more than 400 species of grasses and wildflowers and thousands of species of insects having been identified there. At the most general level, the valley can be classified as a dry yellow pine forest with a number of large open meadows. Plant and animal species that make up

9360-405: The bottom of some scree slopes despite mean annual air temperatures of 6.8–7.5 °C. Scree microclimates maintained by circulating freezing air create micro habitats that support taiga plants and animals that could not otherwise survive regional conditions. A Czech Republic Academy of Sciences research team led by physical chemist Vlastimil Růžička, analyzing 66 scree slopes, published

9490-534: The catchment area of the Merced River above Yosemite, allowing a greater volume of ice to form. Hetch Hetchy is home to a diverse array of plants and animals. Gray pine , incense-cedar , and California black oak grow in abundance. Many examples of red-barked manzanita can be seen along the Hetch Hetchy Road. Spring and early summer bring wildflowers including lupine , wallflower , monkey flower , and buttercup . Seventeen species of bats inhabit

9620-411: The city to conduct an $ 8 million study on how the flooded valley could be drained and restored to its former state. The proposed study would also have been required to identify potential replacements for the water storage capacity and hydroelectric power production. Yosemite Valley Yosemite Valley ( / j oʊ ˈ s ɛ m ə t i / yoh- SEM -ə-tee ; Yosemite , Miwok for "killer")

9750-443: The coarse and fine components, degrading the slope. The predominant processes that degrade a rock slope depend largely on the regional climate (see below), but also on the thermal and topographic stresses governing the parent rock material. Example process domains include: Scree formation is commonly attributed to the formation of ice within mountain rock slopes. The presence of joints , fractures , and other heterogeneities in

9880-415: The cold winter atmosphere and subnivean spaces in screes. As a result, soil, bedrock, and also subterranean voids in screes do not freeze at high elevations. A scree has many small interstitial voids, while an ice cave has a few large hollows. Due to cold air seepage and air circulation, the bottom of scree slopes have a thermal regime similar to ice caves. Because subsurface ice is separated from

10010-414: The cover layer to the debris-ice interface. If the ice is covered by a relatively thin layer of debris (less than around 2 centimeters thick), the albedo effect is most important. As scree accumulates atop the glacier, the ice's albedo will begin to decrease. Instead, the glacier ice will absorb incoming solar radiation and transfer it to the upper surface of the ice. Then, the glacier ice begins to absorb

10140-444: The dam in the 2007 National Park Service budget. Dianne Feinstein opposed this allocation, saying, "I will do all I can to make sure it isn't included in the final bill. We're not going to remove this dam, and the funding is unnecessary." Opponents of dam removal have pointed out that the flooding of the Hetch Hetchy Valley has also deterred the crowds that overrun other areas of Yosemite National Park. Indeed, Hetch Hetchy today remains

10270-468: The dam site. Construction of O'Shaughnessy Dam began in 1919 and was finished in 1923, with the reservoir first filling in May of that year. The dam was then 227 feet (69 m) high; its present height of 312 feet (95 m) was achieved only later, in 1938. On October 28, 1934 – twenty years after the beginning of construction on the Hetch Hetchy project – a crowd of 20,000 San Franciscans gathered to celebrate

10400-462: The damage to the subalpine meadows that surround the Valley and in 1890, the government created a national park that included a much larger territory—enclosing Yosemite Valley and Mariposa Grove. As with Yellowstone, the new federal park was under U.S. Army jurisdiction until 1914. In 1906, the state ceded the Valley and Mariposa Grove to the federal government. The National Park Service , on its creation in 1916, took over Yosemite. Yosemite Valley

10530-400: The dominant tribe. About 1853, his brother, Joseph Screech (credited in some accounts for the original discovery of the valley) blazed the first trail from Big Oak Flat , a mining camp near present-day Lake Don Pedro , for 38 mi (61 km) northeast to Hetch Hetchy Valley. During this time, the upper Tuolumne River, including Hetch Hetchy Valley, was visited by prospectors attracted by

10660-429: The east. The valley provided an escape from the summer heat of the lowlands. They hunted, and gathered seeds and edible plants to furnish themselves winter food, trade items, and materials for art and ceremonial objects. Today, descendants of these people still use milkweed , deergrass , bracken fern , willow , and other plants for a variety of uses including baskets, medicines, and string. Meadow plants unavailable in

10790-433: The eastern end of the valley, is Half Dome , among the most prominent natural features in the Sierra Nevada. Above and to the northeast of Half Dome is Clouds Rest , at 9,926 feet (3,025 m); it is the highest point near Yosemite Valley. Snow melting in the Sierra forms creeks and lakes. In the surrounding region, these creeks flow to the edge of the Valley to form cataracts and waterfalls. A fan of creeks and forks of

10920-402: The energy and uses it in the process of melting. However, once the debris cover reaches 2 or more centimeters in thickness, the albedo effect begins to dissipate. Instead, the debris blanket will act to insulate the glacier, preventing incoming radiation from penetrating the scree and reaching the ice surface. In addition to rocky debris, thick snow cover can form an insulating blanket between

11050-452: The entrance to Yosemite. Scree Scree is a collection of broken rock fragments at the base of a cliff or other steep rocky mass that has accumulated through periodic rockfall . Landforms associated with these materials are often called talus deposits . The term scree is applied both to an unstable steep mountain slope composed of rock fragments and other debris , and to the mixture of rock fragments and debris itself. It

11180-498: The glacier ice begins melting more rapidly or more slowly is determined by the thickness of the layer of scree on its surface. The amount of energy reaching the surface of the ice below the debris can be estimated via the one-dimensional, homogeneous material assumption of Fourier's law : Q = − k ( T s − T i d ) {\displaystyle Q=-k\left({\frac {T_{s}-T_{i}}{d}}\right)} , where k

11310-427: The host rock can be incorporated into the biological structure and weaken the rock. Freeze-thaw action of the entire lichen body due to microclimatic changes in moisture content can alternately cause thermal contraction and expansion, which also stresses the host rock. Lichen also produce a number of organic acids as metabolic byproducts. These often react with the host rock, dissolving minerals, and breaking down

11440-437: The ice surface is substantially lessened. This can act to insulate the glacier from incoming radiation. The albedo , or the ability of a material to reflect incoming radiation energy, is also an important quality to consider. Generally, the debris will have a lower albedo than the glacier ice it covers, and will thus reflect less incoming solar radiation. Instead, the debris will absorb radiation energy and transfer it through

11570-591: The last 30 million years, glaciers have periodically filled much of the valley. The most current glaciation , the Wisconsinian was not, however, the most severe. Ice ages previous to the Wisconsinian were colder and lasted longer. Their glaciers were huge and covered nearly all the landmarks around Yosemite Valley except Half Dome, Eagle Peak , Sentinel Dome , and the top of El Capitan. Wisconsinian glaciers, however, only reached Bridalveil Fall in

11700-451: The least visited developed area of the park. Karin Klein has described Yosemite Valley as "so crammed ... that it looks more like a ripstop ghetto than the site of a nature experience." However, she does support breaching the dam once it has reached the end of its lifespan, and not replacing it. In November 2012, San Francisco voters soundly rejected Proposition F, which would have required

11830-619: The left, and Cathedral Rocks on the right with Bridalveil Fall . Just past this spot the Valley suddenly widens with the Cathedral Spires, then the pointed obelisk of Sentinel Rock to the south. Across the Valley on the northern side are the Three Brothers , rising one above the other like gables built on the same angle – the highest crest is Eagle Peak, with the two below known as the Middle and Lower Brothers. To this point

11960-400: The lowlands were particularly valuable resources to these tribes. For thousands of years, Native Americans subjected the valley to controlled bushfires, which prevented forest from taking over the valley meadows. Periodic clearing of the valley provided ample space for the growth of the grasses and shrubs they relied on, as well as additional room for large game animals such as deer to browse. In

12090-428: The material downslope. In high-altitude arctic and subarctic regions, scree slopes and talus deposits are typically adjacent to hills and river valleys. These steep slopes usually originate from late- Pleistocene periglacial processes. There are five main stages of scree slope evolution: Scree slopes form as a result of accumulated loose, coarse-grained material. Within the scree slope itself, however, there

12220-473: The modern name Hetch Hetchy to Screech's initial arrival in the valley, during which he observed the Native Americans "cooking a variety of grass covered with edible seeds", which they called "hatch hatchy" or "hatchhatchie". Screech reported that the valley was bitterly disputed between the "Pah Utah Indians" (Paiute) and "Big Creek Indians" (Miwok), and witnessed several fights in which the Paiute appeared to be

12350-608: The new park continued their use of Hetch Hetchy Valley – a "sheep-grazing free-for-all [that] threatened to denude the High Sierra meadows" – before disputes over state and private properties in respect to national park boundaries were finally settled in the early 1900s. Interest in using the valley as a water source or reservoir dates back as far as the 1850s, when the Tuolumne Valley Water Company proposed developing water storage there for irrigation. By

12480-416: The north and southwest. When the glacier retreated for the final time, sediment-laden meltwater deposited thick layers of silt , forming the flat alluvial floodplain of the valley floor. Compared with Yosemite Valley, the walls of Hetch Hetchy are smoother and rounder because it was glaciated to a greater extent. This is because the Tuolumne catchment basin above Hetch Hetchy is almost three times as large as

12610-403: The park, including the Valley, were closed due to wildfires in the area. Several trails lead out of the Valley, including Yosemite is now a world rock climbing attraction. The massive 'big walls' of granite have been climbed countless times since the 1950s and have pushed climbers' abilities to new heights. While climbers traditionally take several days to climb the monoliths , bivvying on

12740-494: The protection of both valleys under a single national park. Muir, who himself had briefly worked as a shepherd in Hetch Hetchy, was known for calling sheep "hoofed locusts" because of their environmental impact. Muir's friend Robert Underwood Johnson of the politically influential Century Magazine and several other prominent figures were inspired by Muir's work and helped to get Yosemite National Park established by October 1, 1890. However, ranchers who had previously owned land in

12870-408: The reservoir and return Hetch Hetchy Valley to its former state. Those in favor of dam removal have pointed out that many actions by San Francisco since 1913 have been in violation of the Raker Act, which explicitly stated that power and water from Hetch Hetchy could not be sold to private interests. Hydroelectric power generated from the Hetch Hetchy project is largely sold to Bay Area customers through

13000-487: The river could only be used for public interests. Ultimately, San Francisco sold hydropower from the dam to the Pacific Gas and Electric Company (PG&E), which led to decades of legal wrangling and controversy over terms in the Raker Act. The controversy over Hetch Hetchy was in the context of other political scandals and controversies, especially prevalent in the Taft administration. The Great Alaskan Land Fraud and

13130-542: The rock faces, modern climbing techniques help climbers ascend the cliffs in mere hours. Many climbers stay at Camp 4 before beginning big wall climbs, which became notable after World War II as "a birthplace of rock climbing’s modern age" and was introduced into the National Register of Historic Places in 2003. Half Dome figures prominently on the reverse side of the California state quarter. Hiking to

13260-543: The rock wall can allow precipitation , groundwater , and surface runoff to flow through the rock. If the temperature drops below the freezing point of the fluid contained within the rock, during particularly cold evenings, for example, this water can freeze. Since water expands by 9% when it freezes, it can generate large forces that either create new cracks or wedge blocks into an unstable position. Special boundary conditions (rapid freezing and water confinement) may be required for this to happen. Freeze-thaw scree production

13390-415: The scene was but softened by the haze that hung over the valley – light as gossamer – and by the clouds which partially dimmed the higher cliffs and mountains. This obscurity of vision but increased the awe with which I beheld it, and as I looked, a peculiar exalted sensation seemed to fill my whole being, and I found my eyes in tears with emotion. Camping that night on the Valley floor, the group agreed with

13520-419: The south had permanent Miwok settlements, Hetch Hetchy was only seasonally inhabited. This was likely because of Hetch Hetchy's narrow outlet, which in years of heavy snowmelt created a bottleneck in the Tuolumne River and the subsequent flooding of the valley floor. In the early 1850s, a mountain man by the name of Nathan Screech became the first non-Native American to enter the valley. Local legend attributes

13650-526: The spring, but left rolling fat and hardly able to negotiate the precipitous and difficult defiles out of the mountains in the fall." In 1867, Charles F. Hoffman of the California Geological Survey conducted the first survey of the valley. Hoffman observed a meadow "well timbered and affording good grazing", and noted the valley had a milder climate than Yosemite Valley, hence the abundance of ponderosa pine and gray pine. The valley

13780-506: The substrate into unconsolidated sediments. Scree often collects at the base of glaciers , concealing them from their environment. For example, Lech dl Dragon , in the Sella group of the Dolomites , is derived from the melting waters of a glacier and is hidden under a thick layer of scree. Debris cover on a glacier affects the energy balance and, therefore, the melting process. Whether

13910-601: The suggestion of Dr. Bunnell to call it "Yo-sem-i-ty", mistakenly believing that was the native name. The term is from the Southern Sierra Miwok word Yohhe'meti, meaning "they are killers," which referred to Savage and the Mariposa Battalion. . James Hutchings—who organized the first tourist party to the Valley in 1855—and artist Thomas Ayers generated much of the earliest publicity about Yosemite, creating articles and entire magazine issues about

14040-475: The surface by thin, permeable sheets of sediment, screes experience cold air seepage from the bottom of the slope where sediment is thinnest. This freezing circulating air maintains internal scree temperatures 6.8-9.0 °C colder than external scree temperatures. These <0 °C thermal anomalies occur up to 1000m below sites with mean annual air temperatures of 0 °C. Patchy permafrost , which forms under conditions <0 °C, probably exists at

14170-421: The surface of, or within, rocks. Particularly during the initial colonization process, the lichen often inserts its hyphae into small fractures or mineral cleavage planes that exist in the host rock. As the lichen grows, the hyphae expand and force the fractures to widen. This increases the potential of fragmentation, possibly leading to rockfalls. During the growth of the lichen thallus , small fragments of

14300-399: The top of Half Dome is one of the most popular hikes from the valley, and very crowded. The park now requires permits to use the trail, and in 2011 the permits sold out very quickly after becoming available. The park now uses a lottery system for hikers to apply for permits. Habitation of the Yosemite Valley proper can be traced to about 3,000 years ago when vegetation and game in the region

14430-594: The two largest companies to merge in order that one single concession contract could be given. In 1925 the two family-run companies became the Yosemite Park and Curry Company and went on to build and run the Ahwahnee Hotel as the company headquarters for years, introducing a number of traditions, including the Bracebridge dinner . Curry Village was the site from where villagers and visitors watched

14560-405: The valley back up to recreation, a right that should be provided to the American people because the reservoir is within the legal boundaries of a national park. They acknowledge that a concerted effort would have to be made to control the introduction of wildlife and tourism back into the valley in order to prevent destabilization of the ecosystem, and that it might be decades or even centuries before

14690-665: The valley could be returned to natural conditions. In 1987, the idea of razing the O'Shaughnessy Dam gained an adherent in Don Hodel , Secretary of the Department of the Interior under President Ronald Reagan . Hodel called for a study of the effect of tearing down the dam. The National Park Service concluded that two years after draining the valley, grasses would cover most of its floor and within 10 years, clumps of cone-bearing trees and some oaks would take root. Within 50 years, vegetative cover would be complete except for exposed rocky areas. In this unmanaged scenario, where nature

14820-487: The valley for days, and the wind speed in front of the slide is estimated to have been 300 mph (480 km/h). One person was killed in the slide. In 1987, Congress designated 122 miles of the Merced as a Wild and Scenic River . Yosemite National Park contains 81 of these miles, and the valley contains eight of those miles. This designation will "... preserve the Merced River in free-flowing condition and to protect

14950-470: The valley from roads to the west and pass through the Tunnel View entrance. Visitor facilities are in the center of the valley. There are both hiking trail loops that stay within the valley and trailheads that lead to higher elevations. Yosemite Valley is on the western slope of the Sierra Nevada mountains, 150 miles (240 km) east of San Francisco . It stretches for 7.5 miles (12.1 km) in

15080-532: The valley of European descent, and a few Native Americans, are buried in Yosemite Cemetery . The work of Ayres gave Easterners an appreciation for Yosemite Valley and started a movement to preserve it. Influential figures such as Galen Clark , clergyman Thomas Starr King and leading landscape architect Frederick Law Olmsted were among those who urged Senator John Conness of California to try to preserve Yosemite. President Abraham Lincoln signed

15210-488: The valley, then visiting the waterfalls and other water features, returning east to west with the flow of water. The first view of Yosemite Valley many visitors see is the Tunnel View . So many paintings were made from a viewpoint nearby that the National Park Service named that viewpoint Artist Point . The view from the lower (western) end of the Valley contains the great granite monolith El Capitan on

15340-463: The valley. The El Capitan pluton intruded the valley, forming most of the granitic rock that makes up much of the central part of the valley, including Cathedral Rocks , Three Brothers , and El Capitan. The youngest Yosemite Valley pluton is the 87-million-year-old Half Dome granodiorite, which makes up most of the rock at Glacier Point , the Royal Arches , and its namesake, Half Dome. For

15470-462: The valley. The glaciers widened the valley, but much of its width is in fact due to previous stream erosion and mass wasting along vertical joints in the valley's walls. After the retreat of many of these glaciers, a stand of Ancient Lake Yosemite developed. The valley floor owes its flatness to sediment deposited by these stands (the last glaciers in the valley were small and did not remove much old lake sediment). The last stand of Lake Yosemite

15600-494: The vegetation on the Valley floor, which promoted the black oak and kept the meadows and forests open. This protected the supply of their principal food, acorns , and reduced the chance of ambush. At the time of first European contact, this band was led by Chief Tenaya (Teneiya), who was raised by his mother among the Mono Lake Paiutes . The first non-Native Americans to see Yosemite Valley were probably members of

15730-452: The water and ice simply flow out of the fractures as pressure builds. Many argue that frost heaving , like that known to act in soil in permafrost areas, may play an important role in cliff degradation in cold places. Eventually, a rock slope may be completely covered by its own scree, so that production of new material ceases. The slope is then said to be "mantled" with debris. However, since these deposits are still unconsolidated, there

15860-418: The water delivery. Water from Hetch Hetchy is some of the cleanest municipal water in the United States; San Francisco is one of six U.S. cities not required by law to filter its tap water, although the water is disinfected by ozonation and, since 2011, exposure to UV . The water quality is high because of the unique geology of the upper Tuolumne River drainage basin, which consists mostly of bare granite; as

15990-642: The water quality and the outstandingly remarkable values (ORVs) that make the river worthy of designation." In March 2014, the park system released the Merced Wild and Scenic River Comprehensive Management Plan/EIS to address the preservation of the river, safety, and to improve the visitor experience in the park. The plan will restore meadows and river bank areas and remove non-essential roads. Camping capacity will increase by 37%, and recreational services will be expanded. The plan calls for an 8% increase in parking for day use visitors to Yosemite Valley, including

16120-473: The water's destruction of lichen growth on the canyon walls, which would inevitably be visible at low lake levels. Since the valley was within Yosemite National Park , an act of Congress was needed to authorize the project. The U.S. Congress passed and President Woodrow Wilson signed the Raker Act in 1913, which permitted the flooding of the valley under the conditions that power and water derived from

16250-607: Was a violation of the Raker Act, but he and the city reached an agreement in 1945. In 2015, Restore Hetch Hetchy filed a complaint arguing that the construction of the dam had violated a provision in the constitution of California about water use, but the lawsuit was rejected by an appeals court and later the California State Supreme Court. Preservation groups including the Sierra Club and Restore Hetch Hetchy state that draining Hetch Hetchy would open

16380-641: Was about 5.5 miles (8.9 km) long and was impounded by a terminal moraine near the base of El Capitan. It was later filled by sediment, becoming a swampy meadow. The parallel Tenaya Canyon and Little Yosemite Canyon glaciers were, at their largest, 2,000 feet (610 m) deep where they flowed into the Yosemite Valley near the base of Half Dome. They also formed Clouds Rest behind Half Dome as an arête . Near Glacier Point there are 2,000 feet (610 m) of mostly glacial sediment with at least six separate sequences of Lake Yosemite sediments. Here, huge and highly erosive pre-Wisconsinian glaciers excavated

16510-522: Was completed on the Tuolumne River, flooding the entire valley under the Hetch Hetchy Reservoir . The dam and reservoir are the centerpiece of the Hetch Hetchy Project , which in 1934 began to deliver water 167 miles (269 km) west to San Francisco and its client municipalities in the greater San Francisco Bay Area . Before damming, the high granite formations produced a valley with an average depth of 1,800 ft (550 m) and

16640-487: Was sculpted into its present shape by repeated advance and retreat of the ice, which also removed extensive talus deposits that may have accumulated in the valley since the Sherwin period. At maximum extent, Tioga Glacier may have been 60 mi (97 km) long and up to 4,000 ft (1,200 m) thick, filling Hetch Hetchy Valley to the brim and spilling over the sides, carving out the present rugged plateau country to

16770-432: Was similar to that present today; the western slopes of the Sierra Nevada had acorns, deer, and salmon, while the eastern Sierra had pinyon nuts and obsidian . The prehistory of the area is divided into three cultural phases on archaeological grounds: the "Crane Flat" phase, (1000 BCE to 500 CE) is marked by hunting with the atl atl and the use of grinding stones ; the "Tarmarack" phase (500 to 1200 CE), marked by

16900-492: Was slowly becoming known for its natural beauty, but it was never a popular tourist destination because of extremely poor access and the location of the famous Yosemite Valley just 20 miles (32 km) to the south. Those who did visit it were enchanted by its scenery, but encountered difficulties with the primitive conditions and, in summertime, swarms of mosquitoes. Albert Bierstadt , Charles Dorman Robinson and William Keith were known for their landscapes that drew tourists to

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