From 1795 into the 1850s, the area was part of the Rancho de las Pulgas owned by the Arguello Family of Mexico. After California became part of the United States in 1848, the Pulgas Ranch was sold off in sections for 4 dollars per acre to a few individuals and commercial interests of the rapidly increasing Anglo population.

1848
In the second half of the 19th century, San Francisco Bay became a burgeoning port for tall ships, arriving to exploit the rich gold, silver, and timber resources of California. The shallow bay waters (average 8ft depth in many parts) kept the ships from venturing down to certain areas of the bay. But there was enough depth along the southwestern bay sufficient to take a ship at high tide. The mariners and local folk named some of the tidal water inlets "creeks", but noted that they often flowed backwards! That is because they were actually saltwater tidal sloughs. Names like Seal Creek, Angelo Creek, and O'Neill Creek later would become Seal Slough, Angelo Slough, and O'Neill Slough. It was difficult to navigate the sloughs due to their meandering, multiple branches, and shallowness, however, rowboats could be used to venture ashore.  In 1851, a deep-water channel that ran inland to what is now Redwood City was discovered, leading to larger ships arriving for the redwood lumber, and a wooden shipbuilding industry formed.

Origin and history of Angelo Slough
On December 18, 1850, an englishman named Charles Aubrey Angelo opened a roadhouse called Angelo House. His advertisements in the Daily Pacific News spoke of his boardinghouse as one which possessed "a splendid view of the Harbor and Mt. Diablo." The hilltop ranch house near Angelo's inn was called Bel Monte (beautiful mountain). This eventually led to the name Belmont for the town that developed there. It was located in what is now the intersection of Ralston Avenue and Old County Road in Belmont not far from the slough and creek where the original Ohlone settlement was. In the late 1870's, the Morgan Oyster Company began transplanting live Eastern oysters to the bay waters south of the mouth of Angelo Creek. The industry collapsed after the end of the 19th century, when oyster harvests dropped due to pollution from nearby towns. The raised mud of the oyster bed still exists in shallow water, becoming an island with thousands of birds alighting at low tide. 

Origin of the name Brewer Island
A small group of islands just north of the Port of Redwood City was famous for the huge number of migratory birds. One of these islands was called Guano Island. In the early 20th century, approximately 2,600 acres of islands, sloughs, and tidal marshlands along the western side of San Francisco Bay, between Angelo Creek (Belmont Slough) and  Seal Creek (Marina Lagoon/O'Neill Slough), were owned by Frank Brewer. San Mateo County Reclamation District allowed Brewer to establish dikes along the Bay, reportedly built by the Peabody Dredging Company, around 1901. Thus, the area became known locally as Brewer's Islands. Brewer eventually sold his "land" to the Leslie Salt Company and Schilling Estate Company.

The USGS Topo map San Mateo 7.5' printed in year 1915 (right) shows how the area looked about 100 years ago. Today, Brewer Island is on top of the marshes on the eastern portion of this map. Seal Creek, and portions of Angelo Creek are what are today known as Seal Slough/Marina Lagoon. Part of Angelo Creek is now what is known as O'Neill Slough and Belmont Slough. Part of the main branch of Angelo Creek is now part of Foster City lagoon. Guano Island ("Guano Id." on the map) is now part of Brewer Island. Below the 1915 map, is a graphic overlay tracing of the 1915 map in red over a present-day digital topo map.

Origin and history of Belmont Slough
In the early 1920s, as the little town of Belmont was incorporating, the wheelers and dealers of San Francisco Bay Terminals Company came to the town with a grand idea: they would turn Belmont into a major center for ships. They wanted Belmont to rename itself Port San Francisco, believing that Belmont was close enough to the real San Francisco that eventually, as shippers grew tired of big City politics, they would dock at the "new" Port San Francisco instead. The petition for re-naming failed but the port project moved forward. The San Francisco Terminals Company hired the San Francisco Bay Development Company to begin dredging the channels, basins and slips for the proposed port. The plan envisioned nine miles of deep water dock area, with a capacity of over one hundred vessels. Hence, the project got started in 1926 with the dredging of a straight line channel in the marsh leading from the mouth of Angelo Creek and O'Neill Creek at The Bay directly to Belmont. The work was done by one of the largest clamshell dredgers, the Hercules. By 1929 with the the stock market and public enthusiasm low, the Port San Francisco project was a dud. The channel remained open, according to the topo map of 1941 with the name "Port Of San Francisco" near the mouth of the channel. Now known as the Belmont Channel, this deep-water channel still exists. About the same time, the Angelo Creek and O'Neill Creek delta became known as Belmont Slough, since it was the entry point to the Belmont Channel and the town. A large portion of O'Neill Slough was renamed Belmont Slough on later maps. From 1968 to 1986 a 60-acre aquatic amusement park, Marine World operated at the Belmont Slough/Belmont Channel area, which eventually would become the site of the Oracle software company as Silicon Valley became the driving force. The Belmont Channel is now a reflection pond between hotels, office buildings, and alongside residential houses. Belmont Slough remains as a one of the few somewhat-natural wetlands in the midst of this area of development.

Levees
Levees and dikes were built around several of Brewer's Islands during the early 20th century, as part of salt evaporators and efforts to make cattle-grazing land. Later, some of these levees were built higher, and an even larger one was developed to form the present day Brewer Island, but there remained areas of marsh and tidal islands along the bay and adjacent to Belmont Slough that were not contained within the levees. The levees were strengthened between 1947 and 1960, and continued by Cal Trans as recently as 1983. Large chunks of volcanic rock were brought in to make the main Brewer Island levee bordering The Bay. Various types of landfill was brought to fill up some of the gaps between a few smaller islands within the levee and to raise the level of the main island inside the levee. The pumping operation lasted six years with 14 million cubic yards of sand pumped up from San Francisco Bay at San Bruno Shoal and deposited on Brewer’s Island.

The water of the O'Neill Slough and the Belmont Slough continued to separate Brewer Island from the San Francisco Peninsula, making it difficult to get to and from the island except by boat, the Highway 92 bridge, or the Old San Mateo Bridge [later to become the San Mateo Bridge Fishing Pier]. 

History of Seal Slough (aka Seal Creek), the original channel that is now part of Marina Lagoon, from the 1915 USGS Topo Map.

ca 1915: Between the towns of San Mateo and Belmont, a series of short, intermittent streams drained the east slope of the mountains and hills of The Peninsula. During all but the heaviest rains, their water soaked in to the ground before reaching the bay, probably reemerging at the edge of the salt marsh. In those days, the tidal sloughs of the salt marshes were named as "creeks" independent of any freshwater stream draining an upland that we would think of as a "creek" today. Laurel Creek and the streams to the south would have drained into the O'Neill Creek/Angelo Creek system. To the north of Laurel creek, the streams drained into Seal Creek.

Origin of Foster City
During the late 1950's, T. Jack Foster, in association with Bay Area developer Richard Grant, purchased an option to acquire some of the area inside the levee for the development of a community. This was to become the community of Foster City. This event started the change from what was previously an area devoted to dairy farming and evaporation ponds to become residential and commercial areas. In 1960, the California Legislature created the Estero Municipal Improvement District (EMID), the state's first such public agency. The district was granted most of the governing powers associated with an incorporated municipality, except the powers to zone and approve development and certain police powers. The district was governed by a board of three directors representing the two landowners. A water gate was placed on one of the main branches of Angelo Creek, where the levee crossed it, and the area inside the levee was shaped and tamed with a nautical flair to provide an interesting but very passive lagoon while preserving some of the islands. Angelo Creek became what is today called Foster City Lagoon.

Bay Fill and the Birth of Environmentalism in San Francisco Bay
With the growth of the new community and highway development during the 1960s through present day, several bridges were built to connect Brewer Island with the San Francisco Peninsula. Houses, buildings, and roads displaced wildlife. Soon after T.Jack Foster's development was hailed in the early 60s, the first modern grassroots environmental movement in the Bay Area forced the State of California to acknowledge that the Bay belonged to the public, rejecting the City of Berkeley's plan to develop a similar levee-fill project in the East Bay. An organization called Save The Bay won a legislative moratorium against placing fill in the Bay in 1965, the McAteer-Petris Act. The Bay Conservation and Development Commission (BCDC) was established by the State to plan protection of the Bay, regulate shoreline development, and ensure public access, which at the time was almost non-existent. But by the 1960s, much of the bay's margins had been developed in some way, either by fill or with salt evaporation processing.

Brewer Island and Foster City today
Residential housing developments now surround the 200-acre Foster City Lagoon (relic of Angelo Creek) that winds through the center of the island. It is possible to get around to most places on the island by way of boat, on the San Francisco bay, the sloughs, the internal Foster City Lagoons, or the Marina Lagoon (aka Seal Slough), which borders Brewer Island to the west. Some of the shopping centers and the Community Center have large docks so the residents can go shopping by boat. The lagoons are also used for water recreation and stormwater runoff control. Pumps and opening/closing of water gates at low/high tide controls the levels of the lagoons and herbicides are used to control vegetation in the Foster City Lagoons. Within the lagoons, there are various small islands with short causeways to them from the main Brewers Island which surrounds them. These small islands have residential homes with their own backyard docks. There are many bridges over the various lagoons, and it is difficult to go very far on the island without crossing a few of them. There are many cul-de-sacs due to the water dead ends, and it is like a maze for visitors who don't know their way around the island's roads to get lost. There are very few areas around this part of the bay which remain relatively untouched by development. The remaining natural areas are in the tidal marshlands which are only accessable by foot or small boat with shallow draft. Ducks still often return by instinct to the yards of homes and businesses to nest and waddle around with their ducklings in their ancestral home.

What about an Earthquake?
Whenever there is a large earthquake, such as the Loma Prieta quake in 1989 (Richter scale 7.1), it is necessary to close the bridges until the highway engineers can inspect them. Whenever the bridges are closed, the residents of Brewer Island are basically trapped in various places on the island except for travel by boat. This is not as much of a disaster as it may seem, since many residents of the island have sailboats and motor boats birthed at their backyard docks or sitting on trailers in their backyards.

Is there Salt Evaporators?
There still exists a substantial area of baylands in San Francisco Bay devoted to salt evaporation, but salt harvesting is no longer active in the area around Brewer's Islands and the Belmont Slough islands.

Present situation around the islands
In contrast to the highly-controlled lagoons, to the southeast of Brewer Island is the mostly-natural Belmont Slough/O'Neill Slough system, which connects tidally with the Bay. The Bay tides dramatically affect the level and appearance of the sloughs. The waters of San Francisco Bay wash Brewer Island's eastern and northern shores. Hwy 92, built on concrete stilts over part of the island, cuts diagonally through and leads to the San Mateo Bridge. The outer edges of the island along Belmont Slough and San Francisco Bay are protected undeveloped marshland and bayfront, with public access along a good portion of it. The Bay Trail runs along this area, a popular paved bicycle and walking trail.

FAQ: Is Foster City an Island?
Foster City is built on islands... Brewer Island and several others... but the City of San Mateo, Redwood Shores, and other jurisdictions also share parts of the island. 
A local Foster City politician once ran a campaign with the catchy phrase "Foster City is Not an Island!". He wrote an op-ed piece with that title in a local newspaper, and the phrase was repeated over and over by locals like an urban legend. It even became the subject of arguments locally. However, the politician's campaign phrase was, geographically-speaking, just political retoric, a campaign lie! The campaign aim was actually just attempting to appeal to the people while trying to run for office on the islanders' need to establish better community and governmental relations with San Mateo County government and the neighboring San Francisco Peninsula's cities. It was an effort to change the local laws providing for better county services for Foster City's residents. Foster City is not an island in and of itself, it is just one of the communities on Brewer Island. Foster City covers about 85% of Brewer Island, with the other 15% of the island being shared with the City of San Mateo, town of Redwood Shores, City of Redwood City, City of Belmont, various other state, federal, county, and other jurisdictions. Foster City's city limits also extend halfway across San Francisco Bay, including the many tidal islands which pop up from time to time, and half of the San Mateo Bridge and the Old San Mateo Bridge Fishing Pier.

FAQ: Is Foster City on The Peninsula?
Foster City is known locally as "one of the towns on The Peninsula"... yet it is completely geographically separated from the San Francisco Peninsula by saltwater. What is the story behind this?
Many locals describe Foster City as being on the peninsula. But this is geographically false. Foster City is entirely on an island (actually several islands including the main one, Brewer Island) which is completely surrounded by salt water (San Francisco Bay, Belmont Slough, Marina Lagoon, O'neill Slough). The reason for the confusion about the words "the peninsula" is because the surrounding geographical area that the County of San Mateo is part of, is called the San Francisco Peninsula (in local parlance simply "The Peninsula"). The San Francisco Bay Area (aka "The Bay Area" or simply "The Bay") is described locally as having several different general areas, counterclockwise:
1. The North Bay (aka Marin County).
2. The City (aka City and County of San Francisco)
3. The Peninsula (from San Francisco southward along The Bay's western shore)
4. The South Bay (aka San Jose and Silicon Valley)
5. The East Bay (Oakland and other cities etc)
6. The Delta (Sacremento River Delta) 

FAQ: What's With the word The in California Lingo?
Many highways and geographic features in Californian lingo are preceded with the word "The". This is a carry-over from California's Spanish-language heritage. In Spanish geographic features and common words are often preceded by "El" or "La", which roughtly translates to "The".

FAQ: Where is the San Francisco Peninsula?
The San Francisco Peninsula extends from approximately a line drawn between San Jose and Santa Cruz, and northwest toward the City and County of San Francisco, ending at the Golden Gate Bridge. The San Francisco Peninsula is bordered roughly on the east by San Francisco Bay and on the west by the Pacific Ocean. Technically speaking, the San Francisco Peninsula is also bordered on the east by O'Neill Slough, Marina Lagoon, Belmont Slough, and a number of other sloughs. Sloughs carry saltwater of the bay, and are tidal, so they are tidally a part of the San Francisco Bay.

Below: The image is an aerial photo of the southern end of Brewer Island, where O'Neill Slough meets Belmont Slough at the southern tip of the island. It also shows the water gate bridge on the left side of the photo, where 50 million gallons of water flow each day from O'Neill Slough into Marina Lagoon (aka Seal Slough). Click on the image to load a high resolution aerial photo with more notes, highlighting, and a detailed topo of the island's southern tip area.

.
The image below is an aerial photo of the mouth of Seal Slough where is meets San Francisco Bay. Seal Slough forms the western border of Brewer Island. The level of water in Seal Slough (aka Marina Lagoon) is now controlled by water gates under the bridges at the north and south ends. This often produces different directions of water flow in Marina Lagoon and Laurel Creek which connects with O'Neill Slough at the radio station transmitter area adajacent to the "Belmont Marshland/High Tide Lagoon", along the southern border of Brewer Island next to the Highway 101 Freeway. This often floods Highway 101, with O'Neill Slough taking back its original path whenever there is a winter storm simultaneous with the maximum high tides in January.

Marina Lagoon, also known as Seal Slough
Marina Lagoon, a tidal slough once called Seal Creek before it was diked and dredged, serves as a flood control basin, recreation area, aesthetic amenity, and ecological resource, and is managed to optimize these benefits. The lagoon/sough meanders in a northerly direction from its inlet at O'Neill Slough at the Belmont city limits to its outlet into Seal Slough's mouth delta at San Francisco Bay, a distance of about 4 miles. The lagoon ranges from 300 to 400 feet wide, and averages a depth of 6 feet at mid-channel during the summer. Actually, the Marina Lagoon also includes part of what was once Angelo Creek and O'Neill Creek. A concrete slide gate bridge structure controls inflow from present-day O’Neill Slough, and at the north end another gate bridge separates the lagoon from Seal Slough Delta and San Francisco Bay.

Recreation and enjoyment on the Marina Lagoon
There is no lifeguard on duty. The Harbor Patrol provides enforcement of regulations, boat inspection assistance and first aid, from Memorial Weekend through Labor Day. Fish that frequent the lagoon include striped bass and sturgeon. A healthy lagoon habitat typically supports many of the same species of aquatic invertebrates, fish, and birds that frequent the tidal mudflats and saltmarsh channels. The abundance of waterbirds, shorebirds and the shells along the shore attest to the lagoon's ecological vitality. Birds common to the lagoon include avocets, snowy egrets, night herons, gulls, cormorants, coots, and many ducks, to name a few. The island at the north end of the lagoon, is a designated bird nesting and breeding site. 

Variations in Marina Lagoon's water
By definition, a lagoon is a water body that is subject to tidal action, which may or may not receive fresh water inflows, and can be natural or artificial. Marina Lagoon falls comfortably within this description. Prior to the dredging and development of Marina Lagoon, the area was much like the adjacent Belmont tidal wetlands (where the 1550 kHz AM radio station towers are) and O’Neill Slough to the south, which provide fine examples of tidal salt marsh and tidal flat habitats. Although Seal Slough has been greatly altered from the slough’s original character, Marina Lagoon remains an important component of baylands habitat. The water gate bridge and the radio tower road where O'neill Slough meets Marina Lagoon floods completely over in maximum high tide and storms. The Belmont Tidal Marsh also becomes a lagoon during various times of the year.

The Marina Lagoon’s primary water source is tidal flow from San Francisco Bay through O’Neill Slough, flowing under the water gate bridge at a rate of approximately 52 million gallons per day annualized. Bay water is augmented by perennial low volume fresh water inflow from Laurel Creek and lesser drainage sub-basins within a 10.3 square mile watershed, but comprises only about 0.3 percent of total annual inflow. During the wet season, stormwater runoff can comprise a larger proportion of inflow over the short-term, depending upon the size of the storm event.

The lagoon water level is regulated on a seasonal basis to optimize flood control, recreation, aesthetics, and ecological benefits. The water level is controlled using the O’Neill Slough intake gates and the North End discharge pumps. The pumping plant’s maximum pumping capability of 600 gallons per minute, in combination with the winter design level of el. 95ft is capable of handling a 100-year storm event. 

Aerial Photos of Foster City islands during the 1960s.
Photo source: Foster City

To view a topo map or aerial photo with zoom and pan on the Terraserver
click here: TOPO MAP of Brewer Island