Editing Sacramento River (section)

==Geology==
[[Image:Carquinez Strait aerial view.jpg|thumb|right|alt=Rolling hills covered partially with buildings and roads frame the banks of a large channel of opaque water, which connects two larger bodies of water at the top left and bottom.|The [[Carquinez Strait]], which connects the Sacramento-San Joaquin Delta and Suisun Bay to San Pablo and San Francisco Bays, and then the Pacific. The channel formed from water flooding over the Coast Ranges from a gigantic lake that formed in the Central Valley a few hundred thousand years ago, when the rising mountains blocked the Sacramento's route to the Pacific Ocean.]]

By geologic standards, the Sacramento is a fairly young river; the borders of its watershed began to form only a few million years ago as magma welling up below the Earth's crust pushed up by the [[Pacific Plate]] colliding with the [[North American Plate]] caused the formation of the [[Sierra Nevada (U.S.)|Sierra Nevada]]. Although mountains had existed as early as 100&nbsp;million years ago in this region (before then the land was probably submerged under the Pacific), they were worn by [[erosion]], and the present-day range only formed about 4&nbsp;million years ago.<ref>{{cite web
 |last=Resendes 
 |first=Mary Ann 
 |url=http://www.sierrahistorical.org/archives/geology.html 
 |title=Geology of the Sierra Nevadas 
 |publisher=Central Sierra Historical Society 
 |access-date=August 29, 2010 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20100817124438/http://www.sierrahistorical.org/archives/geology.html 
 |archive-date=August 17, 2010 
}}</ref> The northern part of the Sacramento watershed is more ancient, and was formed by intense volcanic activity over 25&nbsp;million years ago, resulting in lava flows that covered and created the Modoc Plateau, through which the Pit River flows. Mount Shasta and Lassen Peak are among the numerous [[Cascade Volcanoes|Cascade Range volcanoes]] that still stand in the area.<ref>{{cite web
 |last        = Michaelsen
 |first       = Joel
 |url         = http://www.geog.ucsb.edu/~joel/g148_f09/readings/cascades/cascades.html
 |title       = The Cascades and Modoc Plateau Region
 |publisher   = University of Santa Barbara
 |work        = Department of Geography
 |access-date  = August 29, 2010
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20100626202157/http://geog.ucsb.edu/~joel/g148_f09/readings/cascades/cascades.html
 |archive-date = June 26, 2010
}}</ref>

As the Sierra rose, water erosion and glaciation carved deep canyons, depositing massive amounts of sediment to form a coastal plain between the mountains and the Pacific Ocean. About 3&nbsp;million years ago, multiple [[terrane]]s were formed and smashed into the North American Plate from the Pacific Plate, causing the uplift of the [[California Coast Ranges]], enclosing the Sacramento Valley and forcing the streams within to flow south instead of west, forming the ancestral Sacramento River. (The [[Klamath Mountains]], which enclose the northwest part of the Sacramento Basin, were formed in the same way but are much older, dating back 7.5&nbsp;million years.) It is possible that the river once had its outlet in [[Monterey Bay]], and may have played a part in the formation of the {{convert|300|mi|km|adj=on}} [[Monterey Submarine Canyon]] when sea levels were lower during the Ice Ages.<ref>{{cite web
 |url         = http://www.nature.nps.gov/geology/inventory/publications/s_summaries/WHIS_scoping_summary_20041025.pdf
 |title       = Whiskeytown National Recreation Area Geologic Resources Management Issues Scoping Summary
 |last        = Covington
 |first       = Sid
 |publisher   = National Park Service
 |work        = Geologic Resources Division
 |date        = April 20, 2004
 |access-date  = August 29, 2010
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20100528000929/http://www.nature.nps.gov/geology/inventory/publications/s_summaries/WHIS_scoping_summary_20041025.pdf
 |archive-date = May 28, 2010
}}</ref><ref>{{cite web
 |url         = http://sanctuarymonitoring.org/monterey/sections/submarineCanyons/overview.php?sec=sc
 |title       = Monterey Bay Sanctuary: Submarine Canyons
 |publisher   = Sanctuary Integrated Monitoring Network
 |access-date  = August 29, 2010
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20100106112149/http://www.sanctuarymonitoring.org/monterey/sections/submarineCanyons/overview.php?sec=sc
 |archive-date = January 6, 2010
}}</ref>

The Monterey Bay outlet of the Sacramento and San Joaquin rivers was blocked off by uplift about 2&nbsp;million years ago, and runoff from the Sierra began to transform the Central Valley into a gigantic lake, called [[Lake Corcoran|Lake Clyde]]. This lake stretched {{convert|500|mi|km}} north to south and was at least {{convert|1000|ft|m}} deep. About 650,000 years ago the lake catastrophically overflowed, draining into San Francisco Bay and creating the [[Carquinez Strait]], the only major break for hundreds of miles in the Coast Ranges.<ref>{{cite web
 |url         = http://www.nationalatlas.gov/articles/geology/features/centralvalley.html
 |title       = Central Valley
 |publisher   = National Atlas
 |work        = The North American Tapestry of Time and Terrain
 |date        = September 17, 2009
 |access-date  = August 29, 2010
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20101014153202/http://www.nationalatlas.gov/articles/geology/features/centralvalley.html
 |archive-date = October 14, 2010
}}</ref> The narrow outlet trapped some of the sediments of the rivers in the Central Valley, forming the inland [[Sacramento-San Joaquin River Delta]]. Since then, this inland sea has periodically reformed during times of intense flooding, the most recent being the [[Great Flood of 1862]]. Dams, levees and floodways constructed during the 20th century have thus far prevented this phenomenon from re-occurring.<ref>{{cite web
 |last         = Harder
 |first        = Leslie F.
 |url          = http://www.swhydro.arizona.edu/archive/V5_N2/feature3.pdf
 |title        = The Flood Crisis in California's Central Valley
 |publisher    = Southwest Hydrology
 |access-date  = August 29, 2010
 |url-status   = dead
 |archive-url  = https://web.archive.org/web/20100618204806/http://www.swhydro.arizona.edu/archive/V5_N2/feature3.pdf
 |archive-date = June 18, 2010
}}</ref><ref>Kelley and Kelly, pp.5–15</ref>