Editing Sacramento River (section)

===Physiography===
[[Image:CastleCrags.jpg|thumb|right|alt=A cliff of gray serrated rock, on the left, towers above a pine forest before the distant form of a snowcapped mountain.|The [[Castle Crags]], a series of granite peaks rising above the upper Sacramento River canyon just to the right. [[Mount Shasta]], the highest mountain in the Sacramento drainage, is seen in the distance.]]

The basin's diverse geography ranges from the glacier-carved, snowcapped peaks of the Sierra Nevada to the sea-level (and often lower) marshes and farmlands of the Sacramento-San Joaquin Delta. The highest point is {{convert|14104|ft|m}} at [[Mount Shasta]], a dormant [[stratovolcano]] near the headwaters of the Sacramento River.<ref>{{cite gnis
|id=266054
|name=Mount Shasta
|entrydate=1981-01-19
|access-date=August 31, 2010}}</ref> The Sierra Nevada peaks generally decrease in height from south to north&mdash;from over {{convert|10000|ft|m}} in the headwaters of the American River near [[Lake Tahoe]], to {{convert|5000|to|7000|ft|m}} in Lassen County where they adjoin the Cascade Range. On the west side, the Coast Ranges are the opposite, increasing in height to almost {{convert|10000|ft|m}} in the north. The arid volcanic plateaus in the northeast, which are characterized by alternating hills and large sedimentary basins, typically lie at elevations of {{convert|3000|to|5000|ft|m}}.

Most of the Sacramento Valley is below {{convert|300|ft|m}} in elevation; in its lower course, the Sacramento River drops only about {{convert|1|ft|m}} per mile.<ref name="ACMEmapper"/><ref>{{cite web
 |url          = http://www.ucmp.berkeley.edu/science/profiles/erwin_0609geology.php
 |title        = Geologic history of the northern Sierra Nevada
 |publisher    = University of California Berkeley
 |work         = University of California Museum of Paleontology
 |access-date  = August 31, 2010
 |url-status   = dead
 |archive-url  = https://web.archive.org/web/20100718104206/http://www.ucmp.berkeley.edu/science/profiles/erwin_0609geology.php
 |archive-date = July 18, 2010
}}</ref> Between the [[Bajada (geography)|bajadas]] or alluvial slopes extending from the foothills of the Sierra Nevada and Coast Ranges, are the low floodplains of the Sacramento River. The river flows at an elevation somewhat higher than the surrounding terrain due to deposits of sediment over millennia that created raised banks (essentially natural [[levee]]s). The banks separate the river from the lowlands to the east and west that once served as vast overflow basins during winter storms, creating large areas of seasonal [[wetland]]s. Since the 19th century, artificial levee systems have been constructed to enable farming in the fertile flood plain. Today there are {{convert|2000000|acre|km2}} of irrigated farmland in the Sacramento Valley. Due to the reduction of the floodplain area, the speed of flood flow in the Sacramento River has increased, creating a significant hazard for the farms and towns along its course. By the early 20th century engineers had realized not all the floodplains could be safely reclaimed, leading to the intentional creation of flood bypasses where development is limited to annual crops and recreational uses.

Further south, much of the delta region is actually below sea level: subsidence caused by [[wind erosion]] and [[intensive farming]] have caused the land in the delta to gradually sink since the late 19th century. Many of the delta islands would be underwater if not for the maintenance of the levees and pumps that keep them dry. Some of the "islands" are now up to {{convert|25|ft|m}} below the adjacent channels and sloughs.<ref>{{cite web
 |url         = http://ca.water.usgs.gov/archive/reports/fs00500/fs00500.pdf
 |title       = Delta Subsidence in California: The sinking heart of the State
 |publisher   = U.S. Geological Survey
 |access-date  = August 31, 2010
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20100910224619/http://ca.water.usgs.gov/archive/reports/fs00500/fs00500.pdf
 |archive-date = September 10, 2010
}}</ref>