Editing Hetch Hetchy (section)

==Geography==
Before damming, the high granite formations produced a valley with an average depth of {{convert|1800|ft|m|abbr=on}} and a maximum depth of over {{convert|3000|ft|m|abbr=on}}; the length of the valley was {{convert|3|mi|km|abbr=on}} with a width ranging from {{convert|1/8|to|1/2|mi|ft m}}. The valley floor consisted of roughly {{convert|1200|acre|ha|abbr=on}} of meadows fringed by pine forest, through which meandered the Tuolumne River and numerous tributary streams.<ref name=muir>{{cite book|chapter-url=http://www.sierraclub.org/john_muir_exhibit/writings/the_yosemite/chapter_16.aspx|chapter=Hetch Hetchy Valley|title=The Yosemite|first=John|last=Muir|year=1912|location=New York|publisher=The Century Co.}}</ref> [[Kolana Rock]], at {{convert|5772|ft|m|abbr=on}}, is a massive rock spire on the south side of the Hetch Hetchy Valley. [[Hetch Hetchy Dome]], at {{convert|6197|ft|m|abbr=on}}, lies directly north of it. The locations of these two formations roughly correspond with those of [[Middle Cathedral Rock|Cathedral Rocks]] and [[El Capitan]] seen from [[Tunnel View]] in Yosemite Valley.<ref>
{{cite web 
|url=http://www.hetchhetchy.org/originalvalley/natures-garden 
|title=Nature's Garden 
|publisher=Restore Hetch Hetchy 
|access-date=2013-05-30 
|archive-url=https://web.archive.org/web/20130719195110/http://www.hetchhetchy.org/originalvalley/natures-garden 
|archive-date=2013-07-19 
|url-status=dead 
}}
</ref> A broad, low rocky outcrop situated between Kolana Rock and Hetch Hetchy Dome divided the former meadow in two distinct sections.<ref name=hoffmann/>

The valley is fed by the [[Tuolumne River]], [[Falls Creek (California)|Falls Creek]], [[Tiltill Creek]], [[Rancheria Creek (Tuolumne County, California)|Rancheria Creek]], and numerous smaller streams which collectively drain a [[drainage basin|watershed]] of {{convert|459|mi2|km2|abbr=on}}. 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 is now flooded under an average {{convert|300|ft|m|abbr=on}} of water behind the dam, although it occasionally reemerges in droughts, as it did in 1955, 1977, and 1991.<ref>{{cite web
|url=https://vault.sierraclub.org/ca/hetchhetchy/nps_hh_restoration.pdf
|title=Alternatives for Restoration of Hetch Hetchy Valley Following Removal of the Dam and Reservoir
|publisher=Sierra Club
|access-date=2013-05-26}}</ref><ref>{{cite web|url=http://www.pulitzer.org/archives/6889|work=The Pulitzer Prizes |title=Hetch Hetchy Reclaimed: Drain it, then what?}}</ref>

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 is near Yosemite's western boundary, but the long, narrow, fingerlike reservoir stretches eastward for about {{convert|8|mi|km}}.<ref name=sfwater/>
[[File:HetchHetchyWaterfall.jpg|thumb|[[Tueeulala Falls]], {{convert|840|ft|m|abbr=on}}, is located on the north side of the valley.]]

[[Wapama Falls]], at {{convert|1080|ft|m|abbr=on}}, and [[Tueeulala Falls]], at  {{convert|840|ft|m|abbr=on}} – both among the tallest waterfalls in [[North America]] – are both located in Hetch Hetchy Valley.<ref name=hetchhetchy/> [[Rancheria Falls]] is located farther southeast, on Rancheria Creek.<ref>{{cite web|url=http://www.world-of-waterfalls.com/yosemite-rancheria-falls.html|title=Rancheria Falls|work=Yosemite National Park / Hetch Hetchy, California, USA|publisher=World of Waterfalls}}</ref> Formerly, a "small but noisy"{{sfn|Righter|2005|p=15}} waterfall and natural pool existed on the Tuolumne River marked the upper entrance to Hetch Hetchy Valley,<ref>{{cite web |url=http://www.sierraclub.org/ca/hetchhetchy/fall_in_main_tuolumne.html|title=Fall in the Main Tuolumne River at the Head of Hetch Hetchy Valley|work=Requiem for Hetch Hetchy Valley|publisher=Sierra Club}}</ref> 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.{{citation needed|date=May 2022}}

===Geology===
The Hetch Hetchy Valley began as a V-shaped river canyon cut out by 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 National Park|Kings Canyon]] farther to the south.{{sfn|Huber|2007|p=80–83}} During the [[last glacial period]], the Tioga Glacier<ref name="USGS">{{cite book|url=http://geomaps.wr.usgs.gov/parks/yos/topobk.html|title=Geologic Story of Yosemite Valley|publisher=USGS|first=N. King|last=Huber|id=Bulletin 1595|access-date=2013-05-26|archive-url=https://web.archive.org/web/20100528095943/http://geomaps.wr.usgs.gov/parks/yos/topobk.html|archive-date=2010-05-28|url-status=dead}}</ref> formed from extensive icefields in the upper Tuolumne River watershed; between 110,000 and 10,000 years ago Hetch Hetchy Valley was sculpted into its present shape by repeated advance and retreat of the ice, which also removed extensive [[Scree|talus]] deposits that may have accumulated in the valley since the Sherwin period.{{sfn|Huber|2007|p=84}} At maximum extent, Tioga Glacier may have been {{convert|60|mi|km|abbr=on}} long and up to {{convert|4000|ft|m|abbr=on}} thick, filling Hetch Hetchy Valley to the brim and spilling over the sides, carving out the present rugged plateau country to the north and southwest.{{sfn|Matthes|1930|pp=87–90}} 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.{{sfn|Wohlforth|2004|p=419}}

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 the catchment area of the [[Merced River]] above Yosemite, allowing a greater volume of ice to form.<ref name="USGS"/>