Misplaced Pages

#571428

144-628: San Francisco Bay is a large tidal estuary in the U.S. state of California , and gives its name to the San Francisco Bay Area . It is dominated by the cities of San Francisco , San Jose , and Oakland . San Francisco Bay drains water from approximately 40 percent of California. Water from the Sacramento and San Joaquin rivers, and from the Sierra Nevada mountains, flow into Suisun Bay , which then travels through

288-503: A bridge had a widespread public and political appeal. Yet the task was too much of an engineering and economic challenge, since the bay was too wide and too deep there. In 1921, more than forty years after Norton's death, an underground tube was considered, but it became clear that one would be inadequate for vehicular traffic. Support for a trans-bay crossing increased in the 1920s based on the popularity and availability of automobiles. The California State Legislature and governor enacted

432-462: A center anchorage. Rincon Hill is the western anchorage and touch-down for the San Francisco landing of the bridge connected by three shorter truss spans. The eastern crossing, between Yerba Buena Island and Oakland, was a cantilever bridge with a double-tower span, five medium truss spans, and a 14-section truss causeway . Due to earthquake concerns, the eastern crossing was replaced by

576-531: A day on its two decks. It includes one of the longest bridge spans in the United States . The toll bridge was conceived as early as the California gold rush days, with "Emperor" Joshua Norton famously advocating for it, but construction did not begin until 1933. Designed by Charles H. Purcell , and built by American Bridge Company , it opened on Thursday, November 12, 1936, six months before

720-505: A dynamite blast on the eastern side of the island at 12:58 p.m. local time. Former President Herbert Hoover and Governor James Rolph were onsite; the two men were the first to turn over the earth with ceremonial golden spades. Other ceremonies took place simultaneously in San Francisco (on Rincon Hill ) and Oakland Harbor. The Yerba Buena Tunnel opened, along with the rest of the Bay Bridge, on November 12, 1936. As of 2019,

864-604: A former U.S. Congressman from California, traveled to Washington to help persuade President Herbert Hoover and the Reconstruction Finance Corporation to advance $ 62 million to build the bridge. Before work began, 12 massive underwater telephone cables were moved 1,000 feet (300 m) of the proposed bridge route by crews of the Pacific Telephone and Telegraph Co. during the summer of 1931. Construction began on July 9, 1933 after

1008-418: A groundbreaking ceremony attended by former president Herbert Hoover , dignitaries, and local beauty queens. The western section of the bridge between San Francisco and Yerba Buena Island presented an enormous engineering challenge. The bay was up to 100 feet (30 m) deep in places and the soil required new foundation-laying techniques. A single main suspension span some 4,100 feet (1.2 km) in length

1152-573: A harsh environment for organisms. Sediment often settles in intertidal mudflats which are extremely difficult to colonize. No points of attachment exist for algae , so vegetation based habitat is not established. Sediment can also clog feeding and respiratory structures of species, and special adaptations exist within mudflat species to cope with this problem. Lastly, dissolved oxygen variation can cause problems for life forms. Nutrient-rich sediment from human-made sources can promote primary production life cycles, perhaps leading to eventual decay removing

1296-1020: A hotspot for polybrominated diphenyl ether ( PBDE ) flame retardants used to make upholstered furniture and infant care items less flammable. PBDEs have been largely phased out and replaced with alternative phosphate flame retardants. A 2019 San Francisco Estuary Institute (SFEI) study assayed a wide range of these newer flame retardant chemicals in Bay waters, bivalve California mussels ( Mytilus californianus ), and harbor seals ( Phoca vitulina ) which haul out in Corkscrew Slough on Bair Island in San Mateo County , with phosphate flame retardant contaminants such as tris(1,3-dichloro-2-propyl)phosphate (TDCPP) and triphenyl phosphate (TPhP) found at levels comparable to thresholds for aquatic toxicity. Thousands of man-made chemicals are found in Bay water, sediment, and organisms. For many of these, there

1440-702: A law, effective in 1929, to establish the California Toll Bridge Authority (Stats. 1929, Chap 763) and to authorize it and the State Department of Public Works to build a bridge connecting San Francisco and Alameda County (Stats. 1929, Chap 762). The state appointed a commission to evaluate the idea and various designs for a bridge across the Bay, the Hoover-Young Commission . Its conclusions were made public in 1930. In January 1931, Charles H. Purcell ,

1584-544: A major seaport . The Port of Oakland is one of the largest cargo ports in the United States, while the Port of Richmond and the Port of San Francisco provide smaller services. An additional crossing south of the Bay Bridge has long been proposed. San Francisco Bay is popular for sailors (boats, as well as windsurfing and kitesurfing ), due to consistent strong westerly/northwesterly thermally-generated winds – Beaufort force 6 (15–25 knots; 17–29 mph; 8–13 m/s)

SECTION 10

#1732776233572

1728-425: A new crossing that opened on Labor Day 2013. On Yerba Buena Island, the double-decked crossing is a 321-foot (98 m) concrete viaduct east of the west span's cable anchorage, the 540-foot (160 m) Yerba Buena Tunnel through the island's rocky central hill, another 790.8-foot (241.0 m) concrete viaduct, and a longer curved high-level steel truss viaduct that spans the final 1,169.7 feet (356.5 m) to

1872-529: A number of coastal water bodies such as coastal lagoons and brackish seas. A more comprehensive definition of an estuary is "a semi-enclosed body of water connected to the sea as far as the tidal limit or the salt intrusion limit and receiving freshwater runoff; however the freshwater inflow may not be perennial, the connection to the sea may be closed for part of the year and tidal influence may be negligible". This broad definition also includes fjords , lagoons , river mouths , and tidal creeks . An estuary

2016-559: A project which created the artificial Treasure Island . The contract to build the Yerba Buena Cable Anchorage, Tunnel & Viaduct segment was opened for bids on March 28, 1933, and awarded to the low bidder, Clinton Construction Company of California, for $ 1,821,129.50 (equivalent to $ 34 million in 2023 ). Yerba Buena Island was the main site of the official groundbreaking for the Bay Bridge on July 9, 1933, when President Franklin D. Roosevelt remotely set off

2160-562: A safe eating advisory for fish caught in the San Francisco Bay based on levels of mercury or PCBs found in local species. The San Francisco Bay Area Water Trail is a planned system of designated trailheads designed to improve non-motorized small boat access to the bay. The California Coastal Conservancy approved funding in March 2011 to begin implementation of the water trail. Estuary Most existing estuaries formed during

2304-408: A type of ecosystem in some estuaries that have been negatively impacted by eutrophication. Cordgrass vegetation dominates the salt marsh landscape. Excess nutrients allow the plants to grow at greater rates in above ground biomass, however less energy is allocated to the roots since nutrients is abundant. This leads to a lower biomass in the vegetation below ground which destabilizes the banks of

2448-563: A well-mixed water column and the disappearance of the vertical salinity gradient . The freshwater-seawater boundary is eliminated due to the intense turbulent mixing and eddy effects . The lower reaches of Delaware Bay and the Raritan River in New Jersey are examples of vertically homogeneous estuaries. Inverse estuaries occur in dry climates where evaporation greatly exceeds the inflow of freshwater. A salinity maximum zone

2592-436: A wholly marine embayment to any of the other estuary types. The most important variable characteristics of estuary water are the concentration of dissolved oxygen, salinity and sediment load. There is extreme spatial variability in salinity, with a range of near-zero at the tidal limit of tributary rivers to 3.4% at the estuary mouth. At any one point, the salinity will vary considerably over time and seasons, making it

2736-414: A wide effect on the surrounding water bodies.  In turn, this can decrease fishing industry sales in one area and across the country. Production in 2016 from recreational and commercial fishing contributes billions of dollars to the United States' gross domestic product (GDP). A decrease in production within this industry can affect any of the 1.7 million people the fishing industry employs yearly across

2880-559: A widespread distribution in the bay, with uptake in the bay's phytoplankton and contamination of its sportfish. In January 1971, two Standard Oil tankers collided in the bay, creating an 800,000-U.S.-gallon (3,000,000-liter) oil spill disaster , which spurred environmental protection of the bay. In November 2007, a ship named COSCO Busan collided with the San Francisco–Oakland Bay Bridge and spilled over 58,000 U.S. gallons (220,000 liters) of bunker fuel , creating

3024-421: Is 76 feet (23 m) wide and 58 feet (18 m) high overall, and the dimensions of the tunnel interior are 66 feet (20 m) wide and 53 feet (16 m) high. In 1936, it was hailed as the world's largest-bore tunnel. The cross-sectional area of the upper half is 1,500 square feet (140 m ), and the lower half is 1,000 square feet (93 m ). Reminders of the long-gone bridge railway survive along

SECTION 20

#1732776233572

3168-455: Is a dynamic ecosystem having a connection to the open sea through which the sea water enters with the rhythm of the tides . The effects of tides on estuaries can show nonlinear effects on the movement of water which can have important impacts on the ecosystem and waterflow. The seawater entering the estuary is diluted by the fresh water flowing from rivers and streams. The pattern of dilution varies between different estuaries and depends on

3312-525: Is an area of sand dunes now covered by the ocean. The indigenous inhabitants of the San Francisco Bay are Ohlone . The first European to see San Francisco Bay is likely N. de Morena who was left at New Albion at Drakes Bay in Marin County, California , by Sir Francis Drake in 1579 and then walked to Mexico. The first recorded European discovery of San Francisco Bay was on November 4, 1769, when Spanish explorer Gaspar de Portolá , unable to find

3456-489: 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. A shoreline bicycle and pedestrian trail known as the San Francisco Bay Trail encircles the edge of the bay. The San Francisco Bay Area Water Trail , a growing network of launching and landing sites around

3600-513: Is derived from the Latin word aestuarium meaning tidal inlet of the sea, which in itself is derived from the term aestus , meaning tide. There have been many definitions proposed to describe an estuary. The most widely accepted definition is: "a semi-enclosed coastal body of water, which has a free connection with the open sea, and within which seawater is measurably diluted with freshwater derived from land drainage". However, this definition excludes

3744-411: Is formed, and both riverine and oceanic water flow close to the surface towards this zone. This water is pushed downward and spreads along the bottom in both the seaward and landward direction. Examples of an inverse estuary are Spencer Gulf , South Australia, Saloum River and Casamance River , Senegal. Estuary type varies dramatically depending on freshwater input, and is capable of changing from

3888-532: Is in use as an access to the EBMUD treatment plant) and onto 40th St. Due to falling ridership, Sacramento Northern and IER service ended in 1941. On September 13, 1942, a stop was opened at Yerba Buena Island to serve expanded wartime needs on adjacent Treasure Island. Despite the vital role the railroad played, the last train went over the bridge in April 1958. The tracks were removed and replaced with pavement on

4032-566: Is less restricted, and there is a slow but steady exchange of water between the estuary and the ocean. Fjord-type estuaries can be found along the coasts of Alaska , the Puget Sound region of western Washington state , British Columbia , eastern Canada, Greenland , Iceland , New Zealand, and Norway. These estuaries are formed by subsidence or land cut off from the ocean by land movement associated with faulting , volcanoes , and landslides . Inundation from eustatic sea-level rise during

4176-431: Is little or no data on their impacts on the environment or human health, and they are not regulated by state or federal law. These are often referred to as "contaminants of emerging concern." The San Francisco Estuary Institute has studied these chemicals in the Bay since 2001. Scientists have identified the following most likely to have a negative impact on Bay wildlife: San Francisco Bay's profile changed dramatically in

4320-562: 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 Golden Gate International Exposition . From the Second World War until the 1990s, both islands served as military bases and are now being redeveloped. Isolated in the center of the bay is Alcatraz , the site of the famous federal penitentiary. The federal prison on Alcatraz Island no longer functions, but

4464-607: Is shipped throughout the Western United States to bakeries, canneries, fisheries, cheese makers and other food industries and used to de-ice winter highways, clean kidney dialysis machines, for animal nutrition, and in many industries. Many companies have produced salt in the bay, with the Leslie Salt Company the largest private land owner in the Bay Area in the 1940s. Low-salinity salt ponds mirror

San Francisco Bay - Misplaced Pages Continue

4608-632: Is the Colorado River Delta in Mexico, historically covered with marshlands and forests, but now essentially a salt flat. San Francisco%E2%80%93Oakland Bay Bridge The San Francisco–Oakland Bay Bridge , commonly referred to as the Bay Bridge , is a complex of bridges spanning San Francisco Bay in California . As part of Interstate 80 and the direct road between San Francisco and Oakland , it carries about 260,000 vehicles

4752-660: Is the second-largest estuary on the Pacific coast of the Americas, following the Salish Sea in Washington State and British Columbia, Canada. The bay was navigable as far south as San Jose until the 1850s, when hydraulic mining released massive amounts of sediment from the rivers that settled in those parts of the bay that had little or no current. Later, wetlands and inlets were deliberately filled in, reducing

4896-646: Is the whitefish species from the European Alps . Eutrophication reduced the oxygen levels in their habitats so greatly that whitefish eggs could not survive, causing local extinctions. However, some animals, such as carnivorous fish, tend to do well in nutrient-enriched environments and can benefit from eutrophication. This can be seen in populations of bass or pikes. Eutrophication can affect many marine habitats which can lead to economic consequences. The commercial fishing industry relies upon estuaries for approximately 68 percent of their catch by value because of

5040-735: 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. It then connects to the Pacific Ocean via the Golden Gate strait. However, this entire group of interconnected bays is often called the San Francisco Bay . The bay was designated a Ramsar Wetland of International Importance on February 2, 2013, and the Port of Oakland on

5184-522: The Departments of War , Navy , and Commerce . The state applied for permits from the 3 federal departments as required. The permits were granted in January 1932, and formally presented in a ceremony on Yerba Buena Island on February 24, 1932. On May 25, 1931, Governor James Rolph Jr. signed into law two acts: one providing for the financing of state bridges by revenue bonds, and another creating

5328-865: The Dumbarton Rail Bridge , the first bridge crossing San Francisco Bay. The first automobile crossing was the Dumbarton Bridge , completed in January 1927. More crossings were later constructed – the Carquinez Bridge in May 1927, the San Francisco–Oakland Bay Bridge in 1936, the Golden Gate Bridge in 1937, the Richmond–San Rafael Bridge in 1956, and the San Mateo–Hayward Bridge in 1967. During

5472-570: The George Washington Bridge had a longer span between towers. As part of the celebration a United States commemorative coin was produced by the San Francisco Mint . A half dollar , the obverse portrays California's symbol, the grizzly bear , while the reverse presents a picture of the bridge spanning the bay. A total of 71,369 coins were sold, some from the bridge's tollbooths. The Yerba Buena passage utilizes

5616-460: The Golden Gate Bridge . It originally carried automobile traffic on its upper deck, with trucks, cars, buses and commuter trains on the lower, but after the Key System abandoned its rail service on April 20, 1958, the lower deck was converted to all-road traffic as well. On October 12, 1963, traffic was reconfigured to one way traffic on each deck, westbound on the upper deck, and eastbound on

5760-623: The Holocene Epoch has also contributed to the formation of these estuaries. There are only a small number of tectonically produced estuaries; one example is the San Francisco Bay , which was formed by the crustal movements of the San Andreas Fault system causing the inundation of the lower reaches of the Sacramento and San Joaquin rivers . In this type of estuary, river output greatly exceeds marine input and tidal effects have minor importance. Freshwater floats on top of

5904-473: The Holocene epoch with the flooding of river-eroded or glacially scoured valleys when the sea level began to rise about 10,000–12,000 years ago. Estuaries are typically classified according to their geomorphological features or to water-circulation patterns. They can have many different names, such as bays , harbors , lagoons , inlets , or sounds , although some of these water bodies do not strictly meet

San Francisco Bay - Misplaced Pages Continue

6048-632: The Kamchatka Peninsula and Japan. Recent genetic studies show that there is a local stock from San Francisco to the Russian River and that eastern Pacific coastal populations rarely migrate far, unlike western Atlantic Harbor porpoise. The common bottlenose dolphin ( Tursiops truncatus ) has been extending its current range northwards from the Southern California Bight . The first coastal bottlenose dolphin in

6192-408: The Key System . Freight trains never used the bridge. The tracks left the lower deck in San Francisco just southwest of the end of 1st St. They then went along an elevated viaduct above city streets, looping around and into the terminal on its east end. Departing trains exited on the loop back onto the bridge. The loop continued to be used by buses until the terminal's closure in 2010. The tracks left

6336-610: The Mandovi estuary in Goa during the monsoon period. As tidal forcing increases, river output becomes less than the marine input. Here, current induced turbulence causes mixing of the whole water column such that salinity varies more longitudinally rather than vertically, leading to a moderately stratified condition. Examples include the Chesapeake Bay and Narragansett Bay . Tidal mixing forces exceed river output, resulting in

6480-640: The Mid-Atlantic coast, and Galveston Bay and Tampa Bay along the Gulf Coast . Bar-built estuaries are found in a place where the deposition of sediment has kept pace with rising sea levels so that the estuaries are shallow and separated from the sea by sand spits or barrier islands. They are relatively common in tropical and subtropical locations. These estuaries are semi-isolated from ocean waters by barrier beaches ( barrier islands and barrier spits ). Formation of barrier beaches partially encloses

6624-473: The Port of Monterey , continued north close to what is now Pacifica and reached the summit of the 1,200-foot-high (370 m) Sweeney Ridge , now marked as the place where he first sighted San Francisco Bay. Portolá and his party did not realize what they had discovered, thinking they had arrived at a large arm of what is now called Drakes Bay . At the time, Drakes Bay went by the name Bahia de San Francisco and thus both bodies of water became associated with

6768-521: The Sacramento–San Joaquin River Delta remain perhaps California's most important ecological habitats . California's Dungeness crab , California 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

6912-734: The Severn Estuary in the United Kingdom and the Ems Dollard along the Dutch-German border. The width-to-depth ratio of these estuaries is typically large, appearing wedge-shaped (in cross-section) in the inner part and broadening and deepening seaward. Water depths rarely exceed 30 m (100 ft). Examples of this type of estuary in the U.S. are the Hudson River , Chesapeake Bay , and Delaware Bay along

7056-607: The Wisconsin Glaciation , between 15,000 and about 10,000 years ago, the basin which is now filled by the San Francisco Bay was a large river valley with small hills, channeling the Sacramento River through the Golden Gate Strait into the ocean. When the great ice sheets began to melt, around 11,000 years ago, the sea level started to rise rapidly, by about 1 inch per year. Melting glaciers in

7200-563: The Yerba Buena Tunnel , also known as the Yerba Buena Island Tunnel . The tunnel is 76 feet (23 m) wide, 58 feet (18 m) high, and 540 feet (160 m) long. It is the largest diameter transportation bore tunnel in the world. The large amount of material that was excavated in boring the tunnel was used for a portion of the landfill over the shoals lying adjacent to Yerba Buena Island to its north,

7344-478: The black-tailed godwit , rely on estuaries. Two of the main challenges of estuarine life are the variability in salinity and sedimentation . Many species of fish and invertebrates have various methods to control or conform to the shifts in salt concentrations and are termed osmoconformers and osmoregulators . Many animals also burrow to avoid predation and to live in a more stable sedimental environment. However, large numbers of bacteria are found within

SECTION 50

#1732776233572

7488-462: The median of the road for bridge employees; the parking lot is about 1,900 feet (580 m) long, stretching from about 800 feet (240 m) east of the toll plaza to about 100 feet (30 m) west of the metering lights. During the morning commute hours, traffic congestion on the westbound approach from Oakland stretches back through the MacArthur Maze interchange at the east end of

7632-435: The " Bay fill and depth profile " section. ) There are five large islands in San Francisco Bay. Alameda , the largest island, was created when a shipping lane was cut to form the Port of Oakland in 1901. It is now a suburban community. Angel Island was known as " Ellis Island West" because it served as the entry point for immigrants from East Asia. It is now a state park accessible by ferry. Mountainous Yerba Buena Island

7776-565: The 1989 earthquake, was built on fill that had been placed there for the Panama-Pacific International Exposition , although liquefaction did not occur on a large scale. In the 1990s, San Francisco International Airport proposed filling in hundreds more acres 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

7920-551: The 20th century, the bay was subject to the 1940s Reber Plan , which would have filled in parts of the bay in order to increase industrial activity along the waterfront. In 1959, the United States Army Corps of Engineers released a report stating that if current infill trends continued, the bay would be as big as a shipping channel by 2020. This news created the Save the Bay movement in 1960, which mobilized to stop

8064-547: The Bay Area in recent times was spotted in 1983 off the San Mateo County coast in 1983. In 2001, bottlenose dolphins were first spotted east of the Golden Gate Bridge and confirmed by photographic evidence in 2007. Zooarcheological remains of bottlenose dolphins indicated that bottlenose dolphins inhabited San Francisco Bay in prehistoric times until at least 700 years before present, and dolphin skulls dredged from

8208-494: The Bay Bridge, including the construction of the Yerba Buena Tunnel. Before starting excavation, the ground through which the western half of the tunnel would be bored was stabilized by injecting cement grout under pressure through 25 1.5-inch (38 mm) holes bored into the loose rock over the crown of the tunnel. After excavating the western and eastern open portals, three drifts were bored from west to east along

8352-516: The Board of Supervisors, in which compromise with the Central Pacific was recommended; also the bridging of the bay at Ravenswood and the granting of railroad facilities at Mission Bay and on the water front. Wm. C. Ralston, ex-Mayor Selby and James Otis were on this committee. A daily newspaper attempts to account for the advice of these gentlemen to the city by hinting that they were afraid of

8496-471: The Port of Oakland. Some six million cubic yards (160 million cubic feet; 4.6 million cubic meters) of mud from the dredging was deposited at the western edge of Middle Harbor Shoreline Park to become a 188-acre (0.294 sq mi; 0.76 km) shallow-water wetlands habitat for marine and shore life. Further dredging followed in 2011, to maintain the navigation channel. This dredging enabled

8640-628: The Russian Timofei Nikitich Tarakanov , these hunting raids probably wiped out sea otters in the bay. Thousands of sea otter skins were taken to Sitka, then Guangzhou (Canton), China, where they commanded a high price. The United States seized the region from Mexico during the Mexican–American War (1846–1848). On February 2, 1848, the Mexican province of Alta California was annexed to the United States with

8784-487: The San Francisco entrance to the bridge, was jammed with a slowly moving auto caravan. Every available policeman in the department was called to duty to aid in regulating the city's greatest parade of autos. One of the greatest traffic congestions of the evening was at Fifth and Mission Streets, with downtown traffic and bridge-bound traffic snarled in an almost hopeless mass. To add to the confusion, traffic signals jammed and did not synchronize. Police reported that there

SECTION 60

#1732776233572

8928-524: The San Francisco–Oakland Bay Bridge Division of the State Department of Public Works. On September 15, 1931, this new division opened its offices at 500 Sansome Street in San Francisco. During 1931, numerous aerial photographs were taken of the chosen route for the bridge and its approaches. That year, engineers had not determined the final design concept for the western span between San Francisco and Yerba Buena Island, although

9072-526: The Sierra Nevada washed huge amounts of sediment down the Sacramento and San Joaquin rivers, which accumulated on the shores of the bay, forming huge mudflats and marshes that supported local wildlife. By 5000 BC the sea level rose 300 feet (90 m), filling the valley with water from the Pacific. The Farallon Islands are what used to be hills along the old coastline, and Potato Patch Shoal

9216-554: The State Highway Engineer of California, who had also served as the secretary of the Hoover-Young Commission, assumed the position of Chief Engineer for the Bay Bridge. Glenn B. Woodruff served as design engineer for the project. He explained in a 1936 article that several elements of the bridge required not only new designs, but also new theories of design. To make the bridge feasible, a route

9360-400: The United States. Estuaries are incredibly dynamic systems, where temperature, salinity, turbidity, depth and flow all change daily in response to the tides. This dynamism makes estuaries highly productive habitats, but also make it difficult for many species to survive year-round. As a result, estuaries large and small experience strong seasonal variation in their fish communities. In winter,

9504-513: The above definition of an estuary and could be fully saline. Many estuaries suffer degeneration from a variety of factors including soil erosion , deforestation , overgrazing , overfishing and the filling of wetlands. Eutrophication may lead to excessive nutrients from sewage and animal wastes; pollutants including heavy metals , polychlorinated biphenyls , radionuclides and hydrocarbons from sewage inputs; and diking or damming for flood control or water diversion. The word "estuary"

9648-431: The arrival of Europeans. Indigenous peoples used canoes to fish and clam along the shoreline. Sailing ships enabled transportation between the bay and other parts of the world—and served as ferries and freighters within the bay and between the bay and inland ports, such as Sacramento and Stockton. These were gradually replaced by steam-powered vessels starting in the late 19th century. Several shipyards were established around

9792-627: The arrival of the largest container ship ever to enter the San Francisco Bay, the MSC Fabiola . Bay pilots trained for the visit on a simulator at the California Maritime Academy for over a year. The ship arrived drawing less than its full draft of 50 feet 10 inches (15.5 m) because it held only three-quarters of a load after its stop in Long Beach. San Francisco Bay was traversed by watercraft before

9936-400: The average depth of the bay is only as deep as a swimming pool—approximately 12 to 15 ft (4–5 m). Between Hayward and San Mateo to San Jose it is 12 to 36 in (30–90 cm). The deepest part of the bay is under and out of the Golden Gate Bridge, at 372 ft (113 m). In the late 1990s, a 12-year harbor-deepening project for the Port of Oakland began; it

10080-533: The bay for non-motorized small boat users (such as kayakers) is being developed. Parks and protected areas around the bay include Eden Landing Ecological Reserve , Hayward Regional Shoreline , Don Edwards San Francisco Bay National Wildlife Refuge , Hayward Shoreline Interpretive Center , Crown Memorial State Beach , Eastshore State Park , Point Isabel Regional Shoreline , Brooks Island Regional Preserve , and César Chávez Park . The California Office of Environmental Health Hazard Assessment (OEHHA) has developed

10224-464: The bay is one of the busiest cargo ports on the west coast. The bay covers somewhere between 400 and 1,600 square miles (1,000–4,000 km), 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 three to twelve miles (5–19 km) wide east-to-west and somewhere between 48 miles (77 km) and 60 miles (97 km) north-to-south. San Francisco Bay

10368-521: 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 Don Edwards San Francisco Bay National Wildlife Refuge (SFBNWR) in 1972. The bay is also plagued by non-native species. Salt produced from San Francisco Bay is produced in salt evaporation ponds and

10512-415: The bay suggest occasional visitors in historic times. San Francisco Bay faces many of the same water quality issues as other urban waterways in industrialized countries, or downstream of intensive agriculture. According to state water quality regulators, San Francisco Bay waters do not meet water quality standards for the following pollutants: Industrial, mining, and other uses of mercury have resulted in

10656-411: The bay to Oakland was spanned by a 10,176-foot (3.102 km) combination of double cantilever, five long-span through-trusses, and a truss causeway, forming the longest bridge of its kind at the time. The cantilever section was longest in the nation and third-longest anywhere. Much of the original eastern section was founded upon treated wood pilings. Because of the very deep mud on the bay bottom, it

10800-404: The bay's size since the mid-19th century by as much as one third. 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 , many thousands of acres of marshy wetlands at the edges of the bay were, for many years, considered wasted space. As a result, soil excavated for building projects or dredged from channels

10944-478: The bay, augmented during wartime (e.g., the Kaiser Shipyards , Richmond Shipyards ) near Richmond in 1940 for World War II for construction of mass-produced, assembly line Liberty and Victory cargo ships . San Francisco Bay is spanned by nine bridges, eight of which carry cars . The Transbay Tube , an underwater rail tunnel, carries BART services between Oakland and San Francisco. Prior to

11088-452: The bottom where they are harmless. Historically the oysters filtered the estuary's entire water volume of excess nutrients every three or four days. Today that process takes almost a year, and sediment, nutrients, and algae can cause problems in local waters. Some major rivers that run through deserts historically had vast, expansive estuaries that have been reduced to a fraction of their former size, because of dams and diversions. One example

11232-404: The bridge onto the three feeder highways, Interstate 580 , Interstate 880 , and I-80 toward Richmond . Since the number of lanes on the eastbound approach from San Francisco is structurally restricted, eastbound backups are also frequent during evening commute hours. The eastbound bottleneck is not the bridge itself, but the approach, which has just three lanes in each direction, in contrast to

11376-455: The bridge's five. The western section of the Bay Bridge is currently restricted to motorized freeway traffic. Pedestrians, bicycles, and other non-freeway vehicles are not allowed to cross this section. A project to add bicycle/pedestrian lanes to the western section has been proposed but is not finalized. A Caltrans bicycle shuttle operates between Oakland and San Francisco during peak commute hours for $ 1.00 each way. Freeway ramps next to

11520-423: The bridge, the new eastern section is a single deck carrying all eastbound and westbound lanes. Demolition of the old east span was completed on September 8, 2018. The bridge consists of two crossings, east and west of Yerba Buena Island , a natural mid-bay outcropping inside San Francisco city limits. The western crossing between Yerba Buena and downtown San Francisco has two complete suspension spans connected at

11664-614: The bridges and, later, the Transbay Tube, transbay transportation was dominated by fleets of ferryboats operated by the Southern Pacific Railroad and the Key System transit company. However, in recent decades, ferries have returned, primarily serving commuters from Marin County, relieving the traffic bottleneck of the Golden Gate Bridge (see Ferries of San Francisco Bay ). The bay also continues to serve as

11808-608: The cantilever bridge. The toll plaza on the Oakland side (westbound traffic only since 1969) has eighteen toll lanes, with all charges now made either through the FasTrak electronic toll collection system or through invoices mailed through the USPS , based on the license plate of the car per Department of Motor Vehicle records. Metering signals are about 1,000 feet (300 m) west of the toll plaza. Two full-time bus-only lanes bypass

11952-540: The center of the bay, following the ancient drowned river valley. In the 1860s and continuing into the early 20th 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

12096-635: The city would lose its position as the regional center of trade. Businessmen had considered the concept of a bridge spanning the San Francisco Bay since the Gold Rush days. During the 1870s, several newspaper articles explored the idea. In early 1872, a "Bay Bridge Committee" was hard at work on plans to construct a railroad bridge. The April 1872 issue of the San Francisco Real Estate Circular reported on this committee: The Bay Bridge Committee lately submitted its report to

12240-521: The complex is a popular tourist site. Despite its name, Mare Island in the northern part of the bay is a peninsula rather than an island. San Francisco Bay is thought to represent a down-warping of the Earth's crust between the San Andreas Fault to the west and the Hayward Fault to the east, though the precise nature of this remains under study. About 560,000 years ago, a tectonic shift caused

12384-422: The construction of the Bay Bridge was part of the upper deck lining in late summer 1936. This included the emplacement of regularly spaced refuge bays ("deadman holes") along the south wall of the lower deck tunnel, escape alcoves common in all railway tunnels into which track maintenance workers could duck if a train came along. These remain and are visible to eastbound motorists today. The completed tunnel bore

12528-400: The decades surrounding 1900, at the behest of local political officials and following Congressional orders, the U.S. 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. Some of the dredge spoils were initially dumped in the bay shallows (including helping to create Treasure Island on

12672-409: The dissolved oxygen from the water; thus hypoxic or anoxic zones can develop. Nitrogen is often the lead cause of eutrophication in estuaries in temperate zones. During a eutrophication event, biogeochemical feedback decreases the amount of available silica . These feedbacks also increase the supply of nitrogen and phosphorus, creating conditions where harmful algal blooms can persist. Given

12816-419: The ecosystem of the bay, with fish and fish-eating birds in abundance. Mid-salinity ponds support dense populations of brine shrimp , which provide a rich food source for millions of shorebirds. Only salt-tolerant micro-algae survive in the high salinity ponds, and impart a deep red color to these ponds from the pigment within the algae protoplasm. The salt marsh harvest mouse is an endangered species endemic to

12960-401: The effects of modifying the estuarine circulation. Fjord -type estuaries are formed in deeply eroded valleys formed by glaciers . These U-shaped estuaries typically have steep sides, rock bottoms, and underwater sills contoured by glacial movement. The estuary is shallowest at its mouth, where terminal glacial moraines or rock bars form sills that restrict water flow. In the upper reaches of

13104-470: The entrance to the bay, San Francisco was well placed to prosper during the California Gold Rush . Almost all goods not produced locally arrived by ship, as did numerous travelers and erstwhile miners. But after the first transcontinental railroad was completed in May 1869, San Francisco was on the wrong side of the Bay, and separated from the new rail link. Many San Franciscans feared that

13248-601: The estuary impacted by human activities, and over time may shift the basic composition of the ecosystem, and the reversible or irreversible changes in the abiotic and biotic parts of the systems from the bottom up. For example, Chinese and Russian industrial pollution, such as phenols and heavy metals, has devastated fish stocks in the Amur River and damaged its estuary soil. Estuaries tend to be naturally eutrophic because land runoff discharges nutrients into estuaries. With human activities, land run-off also now includes

13392-424: The estuary, the depth can exceed 300 m (1,000 ft). The width-to-depth ratio is generally small. In estuaries with very shallow sills, tidal oscillations only affect the water down to the depth of the sill, and the waters deeper than that may remain stagnant for a very long time, so there is only an occasional exchange of the deep water of the estuary with the ocean. If the sill depth is deep, water circulation

13536-776: The estuary, with only narrow inlets allowing contact with the ocean waters. Bar-built estuaries typically develop on gently sloping plains located along tectonically stable edges of continents and marginal sea coasts. They are extensive along the Atlantic and Gulf coasts of the U.S. in areas with active coastal deposition of sediments and where tidal ranges are less than 4 m (13 ft). The barrier beaches that enclose bar-built estuaries have been developed in several ways: Fjords were formed where Pleistocene glaciers deepened and widened existing river valleys so that they become U-shaped in cross-sections. At their mouths there are typically rocks, bars or sills of glacial deposits , which have

13680-513: The expedition's cartographer, José de Cañizares, gathered the information necessary to produce the first map of the area. A number of place names survive (anglicized) from that first map, including Point Reyes , Angel Island , Farallon Islands , and Alcatraz Island . Alaskan Native sea otter hunters using Aleutian kayaks and working for the Russian–American Company entered San Francisco Bay in 1807 and again over 1810–1811. Led by

13824-477: The first time in 65 years, Pacific Harbor Porpoise ( Phocoena phocoena ) returned to the bay in 2009. Golden Gate Cetacean Research, a non-profit organization focused on research on cetaceans , has developed a photo-identification database enabling the scientists to identify specific porpoise individuals and is trying to ascertain whether a healthier bay has brought their return. Pacific harbor porpoise range from Point Conception , California, to Alaska and across to

13968-609: The fish community is dominated by hardy marine residents, and in summer a variety of marine and anadromous fishes move into and out of estuaries, capitalizing on their high productivity. Estuaries provide a critical habitat to a variety of species that rely on estuaries for life-cycle completion. Pacific Herring ( Clupea pallasii ) are known to lay their eggs in estuaries and bays, surfperch give birth in estuaries, juvenile flatfish and rockfish migrate to estuaries to rear, and anadromous salmonids and lampreys use estuaries as migration corridors. Also, migratory bird populations, such as

14112-555: The former US president Herbert Hoover , Senator William G. McAdoo , and the Governor of California , Frank Merriam . Governor Merriam opened the bridge by cutting gold chains across it with an acetylene cutting torch . The San Francisco Chronicle report of November 13, 1936, read: the greatest traffic jam in the history of S.F., a dozen old-fashioned New Year's eves thrown into one – the biggest and most good-natured crowd of tens of thousands ever to try and walk

14256-561: The former shoals to the north of Yerba Buena Island ) and used to raise islands 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 . Large ships transiting the bay must follow deep underwater channels that are maintained by frequent dredging as

14400-400: The great biodiversity of this ecosystem. During an algal bloom , fishermen have noticed a significant increase in the quantity of fish. A sudden increase in primary productivity causes spikes in fish populations which leads to more oxygen being utilized. It is the continued deoxygenation of the water that then causes a decline in fish populations. These effects can begin in estuaries and have

14544-434: The idea of a double-span suspension bridge was already favored. In April 1932, the preliminary final plan and design of the bridge was presented by Chief Engineer Charles Purcell to Col. Walter E. Garrison, Director of the State Department of Public Works, and to Ralph Modjeski , head of the Board of Engineering Consultants. Both agencies approved and preparation of the final design proceeded. In 1932, Joseph R. Knowland ,

14688-420: The impacts do not end there. Plant death alters the entire food web structure which can result in the death of animals within the afflicted biome . Estuaries are hotspots for biodiversity , containing a majority of commercial fish catch, making the impacts of eutrophication that much greater within estuaries. Some specific estuarine animals feel the effects of eutrophication more strongly than others. One example

14832-501: The infill of wetlands and the bay in general, which had shrunk to two-thirds of its size in the century before 1961. The 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 seven million residents. Despite its urban and industrial character, San Francisco Bay and

14976-467: The large inland Lake Corcoran to spill out the central valley and through the Carquinez Strait , carving out sediment and forming canyons in what is now the northern part of the San Francisco Bay and Golden Gate strait . San Francisco Bay has been filled and emptied of sea water many times during the Pleistocene in accordance with sea level changes caused by glacial advances and retreats. During

15120-480: The largest oil spill in the region since 1996. The bay also has some of the highest levels of dissolved inorganic nitrogen known from any coastal water body, mostly originating from treated wastewater from Publicly owned treatment works . In other bays, such nutrient levels would likely lead to eutrophication , but historically, the bay has had less harmful algal blooms than other water bodies with similar nutrient concentrations. Potential explanations have included

15264-561: The late 19th century and again with the initiation of dredging by the US Army Corps of Engineers in the 20th century. Before about 1860, most bay shores (with the exception of 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

15408-430: The lower deck and the bridge was closed for a month. Reconstruction of the eastern section of the bridge as a causeway connected to a self-anchored suspension bridge began in 2002; the new eastern section opened September 2, 2013, at a reported cost of over $ 6.5 billion; the original estimate of $ 250 million was for a seismic retrofit of the existing span. Unlike the western section and the original eastern section of

15552-571: The lower deck in Oakland. The Interurban Electric Railway tracks ran along Engineer Road and over the Southern Pacific yard on trestles (some of it is still standing and visible from nearby roadways) onto the streets and dedicated right-of-ways in Berkeley, Albany, Oakland and Alameda. The Sacramento Northern and Key System tracks went under the SP tracks through a tunnel (which still exists and

15696-514: The lower deck, with trucks and buses also allowed on the upper deck. In 1986, the bridge was unofficially dedicated to former California governor James Rolph . The bridge has two sections of roughly equal length; the older western section, officially known as the Willie L. Brown Jr. Bridge (after former San Francisco Mayor and California State Assembly Speaker Willie L. Brown Jr. ), connects downtown San Francisco to Yerba Buena Island , and

15840-525: The many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. Excess oxygen-depleting chemicals in the water can lead to hypoxia and the creation of dead zones . This can result in reductions in water quality, fish, and other animal populations. Overfishing also occurs. Chesapeake Bay once had a flourishing oyster population that has been almost wiped out by overfishing. Oysters filter these pollutants, and either eat them or shape them into small packets that are deposited on

15984-422: The marine environment, such as plastics , pesticides , furans , dioxins , phenols and heavy metals . Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation . They also accumulate in benthic environments, such as estuaries and bay muds : a geological record of human activities of the last century. The elemental composition of biofilm reflect areas of

16128-575: The marsh causing increased rates of erosion . A similar phenomenon occurs in mangrove swamps , which are another potential ecosystem in estuaries. An increase in nitrogen causes an increase in shoot growth and a decrease in root growth. Weaker root systems cause a mangrove tree to be less resilient in seasons of drought, which can lead to the death of the mangrove. This shift in above ground and below ground biomass caused by eutrophication could hindered plant success in these ecosystems. Across all biomes, eutrophication often results in plant death but

16272-533: The name. Eventually, the larger, more important body of water fully appropriated the name 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. Ayala continued to explore the San Francisco Bay Area and

16416-402: The newer east bay section connects the island to Oakland. The western section is a double suspension bridge with two decks, westbound traffic being carried on the upper deck while eastbound is carried on the lower one. The largest span of the original eastern section was a cantilever bridge . During the 1989 Loma Prieta earthquake , a portion of the eastern section's upper deck collapsed onto

16560-440: The now off-balance nitrogen cycle , estuaries can be driven to phosphorus limitation instead of nitrogen limitation. Estuaries can be severely impacted by an unbalanced phosphorus cycle, as phosphorus interacts with nitrogen and silica availability. With an abundance of nutrients in the ecosystem, plants and algae overgrow and eventually decompose, which produce a significant amount of carbon dioxide. While releasing CO 2 into

16704-451: The path of the tunnel: one at the crown and the other two at the lower corners. The first drift broke through in July 1934, approximately one year after the start of construction. A ceremonial party led by Governor Merriam celebrated the completion of the first 12-foot-square (3.7 m) drift on July 24 by walking through it, followed by a short speech. The space between the three drifts

16848-415: The presence of intensive "top-down control" from grazing clams like Potamocorbula , high sediment supply limiting light availability for the algae, and intensive tidal mixing. The occurrence of an unprecedented harmful algal bloom of Heterosigma akashiwo in 2022, resulting in mass fish deaths and anoxia, suggests that the mechanisms of control on algal growth may be eroding. The bay was once considered

16992-504: The railroad company, and therefore made their recommendations to suit its interests. The self-proclaimed Emperor Norton decreed three times in 1872 that a suspension bridge be constructed to connect Oakland with San Francisco. In the third of these decrees, in September 1872, Norton, frustrated that nothing had happened, proclaimed: WHEREAS, we issued our decree ordering the citizens of San Francisco and Oakland to appropriate funds for

17136-461: 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 19th 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

17280-837: The rivers. San Francisco Bay is recognized for protection by the California Bays and Estuaries Policy , with oversight provided by the San Francisco Estuary Partnership . 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 Ridgway's 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

17424-427: The seawater in a layer that gradually thins as it moves seaward. The denser seawater moves landward along the bottom of the estuary, forming a wedge-shaped layer that is thinner as it approaches land. As a velocity difference develops between the two layers, shear forces generate internal waves at the interface, mixing the seawater upward with the freshwater. An examples of a salt wedge estuary is Mississippi River and

17568-411: The sediment which has a very high oxygen demand. This reduces the levels of oxygen within the sediment often resulting in partially anoxic conditions, which can be further exacerbated by limited water flow. Phytoplankton are key primary producers in estuaries. They move with the water bodies and can be flushed in and out with the tides . Their productivity is largely dependent upon the turbidity of

17712-515: The signing of the Treaty of Guadalupe Hidalgo . A year and a half later, 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. In 1921, a tablet was dedicated by a group of men in downtown San Francisco, marking the site of the original shoreline. The tablet reads: "This tablet marks the shore line of San Francisco Bay at

17856-412: The south side of the lower Yerba Buena Tunnel. These are the regularly spaced refuge bays ("deadman holes"), escape alcoves common in all railway tunnels, along the wall, into which track maintenance workers could safely retreat if a train came along. (The north side, which always carried only motor traffic, lacks these holes.) The bridge opened on November 12, 1936, at 12:30 p.m. In attendance were

18000-426: The streets and guide their autos on them – This was the city last night, the night of the bridge opening with every auto owner in the bay region, seemingly, trying to crowd his machine onto the great bridge. And those who tried to view the brilliantly lighted structure from the hilltops and also view the fireworks display were numbered also in the thousands. Every intersection in the city, particularly those near

18144-633: The survey of a suspension bridge from Oakland Point via Goat Island; also for a tunnel; and to ascertain which is the best project; and whereas the said citizens have hitherto neglected to notice our said decree; and whereas we are determined our authority shall be fully respected; now, therefore, we do hereby command the arrest by the army of both the Boards of City Fathers if they persist in neglecting our decrees. Given under our royal hand and seal at San Francisco, this 17th day of September, 1872. Unlike most of Emperor Norton's eccentric ideas, his decree to build

18288-662: The time of the discovery of gold in California, January 24, 1848. Map reproduced above delineates old shore line. Placed by the Historic Landmarks committee, Native Sons of the Golden West , 1921." The bay became the center of American settlement and commerce in the Far West through most of the remainder of the 19th century. During the California Gold Rush (1848–1855), San Francisco Bay suddenly became one of

18432-407: The toll booths and metering lights around the right (north) side of the toll plaza; other high occupancy vehicles can use these lanes during weekday morning and afternoon commute periods. The two far-left toll lanes are high-occupancy vehicle lanes during weekday commute periods. Radio and television traffic reports will often refer to congestion at the toll plaza, metering lights, or a parking lot in

18576-548: The tunnel lacks an official name. Construction of the Bridge Railway began on November 29, 1937, with the laying of the first ties. The first train was run across the Bay Bridge on September 23, 1938, a test run utilizing a Key System train consisting of two articulated units with California Governor Frank Merriam at the controls. On January 14, 1939, the San Francisco Transbay Terminal

18720-428: The tunnel provide access to Yerba Buena Island and Treasure Island . Because the toll plaza is on the Oakland side, the western span is a de facto non-tolled bridge; traffic between the island and the main part of San Francisco can freely cross back and forth. Those who only travel from Oakland to Yerba Buena Island, and not the entire length to the main part of San Francisco, still must pay the full toll. Developed at

18864-414: The tunnel roof and lower deck was excavated using a power shovel. By May 1935, work on removing the core was progressing and 40 steel ribs had been placed; concrete embedment was just starting. Removal of the core was completed on November 18, 1935. Once the excavation was complete, the upper deck was placed and the interior ceiling above the upper deck was lined with tiles. The last concrete poured during

19008-456: The volume of freshwater, the tidal range, and the extent of evaporation of the water in the estuary. Drowned river valleys are also known as coastal plain estuaries. In places where the sea level is rising relative to the land, sea water progressively penetrates into river valleys and the topography of the estuary remains similar to that of a river valley. This is the most common type of estuary in temperate climates. Well-studied estuaries include

19152-453: The water and atmosphere, these organisms are also intaking all or nearly all of the available oxygen creating a hypoxic environment and unbalanced oxygen cycle . The excess carbon in the form of CO 2 can lead to low pH levels and ocean acidification , which is more harmful for vulnerable coastal regions like estuaries. Eutrophication has been seen to negatively impact many plant communities in estuarine ecosystems . Salt marshes are

19296-835: The water. The main phytoplankton present are diatoms and dinoflagellates which are abundant in the sediment. A primary source of food for many organisms on estuaries, including bacteria , is detritus from the settlement of the sedimentation. Of the thirty-two largest cities in the world in the early 1990s, twenty-two were located on estuaries. As ecosystems, estuaries are under threat from human activities such as pollution and overfishing . They are also threatened by sewage, coastal settlement, land clearance and much more. Estuaries are affected by events far upstream, and concentrate materials such as pollutants and sediments. Land run-off and industrial, agricultural, and domestic waste enter rivers and are discharged into estuaries. Contaminants can be introduced which do not disintegrate rapidly in

19440-432: The wetlands of the San Francisco Bay with a high salt tolerance. It needs native pickleweed , which is often displaced by invasive cordgrass, for its habitat. The seasonal range of water temperature in the bay is from January's 53 °F (12 °C) to September's 60 °F (16 °C) when measured at Fort Point , which is near the southern end of the Golden Gate Bridge and at the entrance to San Francisco Bay. For

19584-491: The world's great seaports, dominating shipping in the American West until the last years of the 19th century. The bay's regional importance increased further when the first transcontinental railroad was connected to its western terminus at Alameda on September 6, 1869. The terminus was switched to the Oakland Long Wharf two months later on November 8, 1869. In 1910, the Southern Pacific railroad company built

19728-440: Was chosen via Yerba Buena Island , which would reduce both the material and the labor needed. Since Yerba Buena Island was a U.S. Navy base at the time, the state had to gain approval from Congress for this purpose as it regulates and controls all federal lands and the armed services . After a great deal of lobbying, California received Congressional approval to use the island on February 20, 1931, subject to final approvals by

19872-418: Was considered but rejected, as it would have required too much fill and reduced wharfage space at San Francisco, had less vertical clearance for shipping, and cost more than the design ultimately adopted. The solution was to construct a massive concrete anchorage halfway between San Francisco and the island, and to build a main suspension span on each side of this central anchorage. East of Yerba Buena Island,

20016-608: Was dedicated. The following morning, January 15, 1939, the electric interurban trains started in revenue service, running along the south side of the lower deck of the bridge. The terminal originally was supposed to open at the same time as the Bay Bridge, but had been delayed. Trains over the Bridge Railway were operated by the Sacramento Northern Railroad ( Western Pacific ), the Interurban Electric Railway ( Southern Pacific ) and

20160-646: Was largely completed by September 2009. Previously, the bay waters and harbor facilities only allowed for ships with a draft of 46 ft (14 m), but dredging activities undertaken by the United States Army Corps of Engineers in partnership with the Port of Oakland succeeded in providing access for vessels with a 50-foot (15 m) draft. Four dredging companies were employed in the US$ 432 ;million project, with $ 244 million paid for with federal funds and $ 188 million supplied by

20304-436: Was no lessening of the traffic over the bridge, all lanes being crowded with Oakland- or San-Francisco-bound machines far into the night. The total cost was US$ 77 million. Before opening the bridge was blessed by Cardinal Secretary of State Eugene Cardinal Pacelli , later Pope Pius XII . Because it was in effect two bridges strung together, the western spans were ranked the second and third largest suspension bridges . Only

20448-428: Was not practical to reach bedrock, although the lower levels of the mud are quite firm. Long wooden pilings were crafted from entire old-growth Douglas fir trees, which were driven through the soft mud to the firmer bottom layers. The construction project had casualties: twenty-four men would die while constructing the bridge. California Department of Transportation engineer C.H. Purcell served as chief engineer for

20592-529: Was often dumped onto the wetlands and other parts of the bay as landfill. From the mid-19th century through the late 20th century, more than a third of the original bay was filled and often built on. The deep, damp soil in these areas is subject to soil 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. The Marina District of San Francisco, hard hit by

20736-429: Was then excavated, resulting in a single arch-shaped bore (in cross-section), and the tunnel roof was constructed using 16-inch (410 mm) steel I-beam ribs spaced 3 feet (0.91 m) apart to support the rock, which were then embedded in concrete up to 3 feet (0.91 m) thick at the crown. No cave-ins occurred during the excavation of the tunnel. After the roof was completed, the remaining core of rock between

#571428