San Francisco Bay

From Wikipedia, the free encyclopedia

This article is about the physical feature known as the San Francisco Bay. For the geographical region surrounding the San Francisco Bay, see San Francisco Bay Area.

San Francisco Bay, San Pablo Bay, and the Golden Gate

San Francisco Bay is a shallow, productive estuary through which water draining approximately forty percent of California, flowing in the Sacramento and San Joaquin rivers from the Sierra Nevada mountains, enters the Pacific Ocean. Technically, both rivers flow into Suisun Bay, which help flows through the Carquinez Strait to meet with the Napa River at the entrance to San Pablo Bay, which connects at its south end to San Francisco Bay, although the entire group of interconnected bays are often referred to as "the San Francisco Bay."

San Francisco Bay is located in the US state of California, surrounded by a contiguous region known as the San Francisco Bay Area, dominated by the big cities San Francisco, Oakland, and San Jose.

1 Size
2 Role in California settlement
3 Ecology
4 Bay Fill and Depth Profile
5 Miscellaneous
6 Photography
7 See also
8 References
9 External links

[edit] Size

The Bay covers somewhere between 400[1] and 1600[2] square miles (1040 to 4160 square kilometres), depending on which sub-bays (such as San Pablo Bay), estuaries, wetlands, and so on are included in the measurement. The main part of the Bay measures 3 to 12 miles (5 to 20 km) wide east-to-west and somewhere between 48 miles (77 km)¹ and 60 miles (97 km)² north-to-south. One difficulty in obtaining accurate measurements is that the wetlands and inlets of the bay have been gradually and deliberately filled in, changing the Bay's size since the mid-1800s by as much as one third or even more. Recently, large areas of wetlands have been restored, further confusing the issue of the Bay's size.

Despite its value as a waterway and harbor, the many thousands of acres (several km²) of marshy wetlands forming the edges of the bay were considered for many years to be wasted space. As a result, soil excavated for building projects or dredged from channels was often dumped onto the wetlands and into other parts of the bay as landfill. From the mid-1800s through the late 1900s, more than a third of the original bay was filled and often built on. The deep, damp soil in these areas is subject to liquefaction during earthquakes, and most of the major damage close to the Bay in the Loma Prieta earthquake of 1989 occurred to structures on these areas. In the 1990s, the San Francisco International Airport proposed filling in hundreds more acres (km²) to extend its overcrowded international runways in exchange for purchasing other parts of the bay and converting them back to wetlands. The idea was, and remains, controversial. (For further details, see the "Bay Fill and Depth Profile" section.)

[edit] Role in California settlement

The first recorded European discovery of the San Francisco Bay was on November 4, 1769 when Spanish explorer Gaspar de Portolà, unable to find the port of Monterey, California, moored his ship close to what is now Pacifica. Short on water and food, Portolà and an expeditionary crew of 63 men and 200 horses began an overland journey that took them to the summit of the 1200 foot high Sweeney Ridge, where he sighted the San Francisco Bay. Sweeney Ridge is located in northern San Mateo County, California and is now a part of the Golden Gate National Recreation Area where a monument marks the discovery site. The site is listed on the National Register of Historic Places (NPS-68000022) as No. 394: Site of the Discovery of San Francisco Bay.

The first European to enter the bay is believed to have been the Spanish explorer Juan de Ayala, who passed through the Golden Gate on August 5, 1775 in his ship the San Carlos, and moored in a bay of Angel Island now known as Ayala Cove.

This famous bay was the center of American settlement in the Far West during the 19th century. From the 1820s onward, American presidents and expansionists coveted the bay as a great natural harbor in the Pacific. After many failed efforts to buy the bay and varying areas around it, the US Navy and Army seized the region from Mexico during the Mexican-American War (1845-1848). On February 2, 1848 California seceded from Mexico with the signing of the Guadalupe-Hidalgo treaty. A year and a half after gaining independence, California requested to join the United States on December 3, 1849 and was accepted as the 31st State of the union on September 9, 1850. During the California gold rush of 1848-1850s, San Francisco Bay instantly became one of the world's greatest seaports, dominating shipping and transportation in the American West until the last years of the nineteenth century. The bay's regional importance became paramount when in 1869 the transcontinental railroad located its western terminus in Oakland. San Francisco Bay continues to support some of the densest industrial production and urban settlement in the United States. The San Francisco Bay Area is the American West's second-largest urban area with approximately 8 million residents.

San Francisco Bay from space, September 1994

[edit] Ecology

Despite its urban and industrial character, San Francisco Bay and the Sacramento-San Joaquin Delta remain perhaps California's most important ecological habitats. California's Dungeness crab, Pacific halibut, and Pacific salmon fisheries rely on the bay as a nursery. The few remaining salt marshes now represent most of California's remaining salt marsh, supporting a number of endangered species and providing key ecosystem services such as filtering pollutants and sediments from the rivers. Most famously, the bay is a key link in the Pacific Flyway. Millions of waterfowl annually use the bay shallows as a refuge. Two endangered species of birds are found here: the California least tern and the California clapper rail. Exposed bay muds provide important feeding areas for shorebirds, but underlying layers of bay mud pose geological hazards for structures near many parts of the bay perimeter. San Francisco Bay provided the nation's first wildlife refuge, Oakland's artificial Lake Merritt (constructed in the 1860s) and America's first urban National Wildlife Refuge, the San Francisco Bay National Wildlife Refuge (SFBNWR) (1972).

USGS Satellite photo of the San Francisco Bay Area.

Tellingly, much of the SFBNWR consists of salt evaporation ponds purchased or leased from Leslie Salt Company and its successor, Cargill Corporation. These salt ponds produce salt for a variety of industrial purposes, including chlorine bleach and plastics manufacture, as well as supporting dense populations of brine shrimp, and therefore serving as feeding areas for waterfowl. In 2003, California and Cargill entered one of the largest private land purchases in American history, with the state and federal governments paying about $200 million for 16,000 acres (65 km²) of salt ponds in the south bay. SFBNWR and state biologists hope to restore some of the recently purchased ponds as tidal wetlands.

The seasonal range of water temperature in the Bay is from about 8°C to about 23°C.

San Francisco Bay ca. 1770-1820

San Francisco Bay ca. 1985-1996

[edit] Bay Fill and Depth Profile

San Francisco Bay's profile changed dramatically in the late nineteenth century and again with the initiation of dredging by the US Army Corps of Engineers in the twentieth century. Before about 1860, most bay shores (exception: rocky shores such as those in Carquinez Strait, along Marin shoreline, Point Richmond, Golden Gate area) contained extensive wetlands that graded nearly invisibly from freshwater wetlands to salt marsh and then tidal mudflat. A deep channel ran through the center of the bay, following the ancient drowned river valley.

In the 1860s and continuing into the early twentieth century, miners dumped staggering quantities of mud and gravel from hydraulic mining operations into the upper Sacramento and San Joaquin Rivers. GK Gilbert's estimates of debris total more than eight times the amount of rock and dirt moved during construction of the Panama Canal. This material flowed down the rivers, progressively eroding into finer and finer sediment, until it reached the bay system. Here some of it settled, eventually filling in Suisun Bay, San Pablo Bay, and San Francisco Bay, in decreasing order of severity.

By the end of the nineteenth century, these "slickens" had filled in much of the shallow bay flats, raising the entire bay profile. New marshes were created in some areas.

In the last years of the nineteenth and first decades of the twentieth century, at the behest of local political officials and following Congressional orders, the US Army Corps began dredging the Sacramento and San Joaquin Rivers and the deep channels of San Francisco Bay. This work has continued without interruption ever since, an enormous federal subsidy of San Francisco Bay shipping. Some of the dredge spoils were initially dumped in the bay shallows (including helping to create "Treasure Island" on the former shoals to the north of Yerba Buena Island) and used to raise an island in the Sacramento-San Joaquin Delta. The net effect of dredging has been to maintain a narrow deep channel - deeper perhaps than the original bay channel - through a much shallower bay. At the same time, most of the marsh areas have been filled or blocked off from the bay by dikes.

[edit] Miscellaneous

San Francisco Bay is spanned by five bridges: the Golden Gate Bridge (which was the largest single span suspension bridge ever built at the time of its construction), the Richmond-San Rafael Bridge, the San Francisco-Oakland Bay Bridge, the Hayward-San Mateo Bridge and the Dumbarton Bridge.

There are four large islands in San Francisco Bay. Isolated in the center of the Bay is Alcatraz, the site of the famous and allegedly escape-proof federal penitentiary. Mountainous Yerba Buena Island is pierced by a tunnel linking the east and west spans of the San Francisco-Oakland Bay Bridge. Attached to the north is the artificial and flat Treasure Island, site of the 1939 World's Fair. Closest to shore, Angel Island was known as "Ellis Island West" because it served as the entry point for immigrants from East Asia. Raccoon Strait, between Tiburon and Angel Island, is the deepest part of the Bay.) The federal prison on Alcatraz Island no longer functions, and the complex is now a popular tourist site.

Alcatraz at dawn on San Francisco Bay

The southern part of the Bay, around the city of San Jose, is known as Silicon Valley for its high concentration of high-tech, semiconductor and computer-related industry.

The San Francisco Bay is a mecca for sailors, due to consistent strong winds (Beaufort force 6 is common on summer afternoons) and protection from large open ocean swells. Yachting and yacht racing are popular pastimes and the San Francisco Bay area is home to many of the world's top sailors.

Arguably the most famous individual whale in history, Humphrey the whale, entered San Francisco Bay twice on errant migrations, and was successfully rescued and redirected each time.