In 2006, a male and female California golden beaver arrived in Alhambra Creek in downtown Martinez.
The beavers built a dam 30 feet (9 m) wide and at one time 6 feet (2 m) high, and chewed through half the willows and other creekside landscaping the city planted as part of its US$9.7 million 1999 flood-improvement project.
The City Council wanted to remove the beavers because of fears of flooding, ironically, as the worst flood since the flood control project was in 2005, two years before the beavers came.
Local residents organized to protect them, forming an organization called Worth a Dam.
Resolution included installing a flow device pipe through the beaver dam so that the pond's water level could not become excessive.
Now protected, the beaver have transformed Alhambra Creek from a trickle into multiple dams and beaver ponds, which in turn, led to the return of numerous birds, steelhead trout (Oncorhynchus mykiss) and river otter (Lontra canadensis) in 2008, and mink (Neovison vison) in 2009.
Examples of the impact of the beaver as a keystone species in 2010, include a green heron (Butorides virescens) catching a tule perch (Hysterocarpus traskii traskii), the first recorded sighting of the perch in Alhambra Creek and the December arrival of a pair of hooded mergansers (Lophodytes cucullatus) (see photos).
The beaver parents have produced babies every year since their 2006 arrival.
However, in June, 2010, after birthing and successfully weaning triplets this year (and quadruplets the previous three years), "Mom Beaver" died of natural causes.

In November, 2009 the Martinez City Council approved the placement of an 81 tile wildlife mural on the Escobar Street bridge.
 The mural was created by schoolchildren and donated by Worth a Dam to memorialize the beavers and other fauna in Alhambra Creek.

The Martinez beavers probably originated from the Sacramento-San Joaquin River Delta.
Historically, before the California Fur Rush of the late 18th and early 19th centuries, the Delta probably held the largest concentration of beaver in North America.
It was California's early fur trade, more than any other single factor, that opened up the West, and the San Francisco Bay Area in particular, to world trade.
The Spanish, French, English, Russians and Americans engaged in the California fur trade before 1825, harvesting prodigious quantities of beaver, river otter, marten, fisher, mink, fox, weasel, harbor and fur seals and sea otter.
When the coastal and oceanic fur industry began to decline, the focus shifted to California's inland fur resources.
Between 1826 and 1845 the Hudson's Bay Company sent parties out annually from Fort Astoria and Fort Vancouver into the Sacramento and the San Joaquin valleys as far south as French Camp on the San Joaquin River.
These trapping expeditions must have been extremely profitable to justify the long overland trip each year.
It appears that the golden beaver (castor canadensis, subspecies: subauratus) was one of the most valued of the animals taken, and apparently was found in great abundance.
Thomas McKay reported that in one year the Hudson's Bay Company took 4,000 beaver skins on the shores of San Francisco Bay.
At the time, these pelts sold for US$2.50 a pound or about US$4.00 each.
The Delta area incidentally, is probably where McKay was so successful, rather than the Bay itself.
In 1840, explorer Captain Thomas Farnham wrote that beaver were very numerous near the mouths of the Sacramento and San Joaquin rivers and on the hundreds of small "rushcovered" islands.
Farnham, who had travelled extensively in North America, said: "There is probably no spot of equal extent in the whole continent of America which contains so many of these muchsought animals."
In 2006, a male and female California golden beaver arrived in Alhambra Creek in downtown Martinez. The beavers built a dam 30 feet (9 m) wide and at one time 6 feet (2 m) high, and chewed through half the willows and other creekside landscaping the city planted as part of its US$9.7 million 1999 flood-improvement project. The City Council wanted to remove the beavers because of fears of flooding, ironically, as the worst flood since the flood control project was in 2005, two years before the beavers came. Local residents organized to protect them, forming an organization called Worth a Dam. Resolution included installing a flow device pipe through the beaver dam so that the pond's water level could not become excessive. Now protected, the beaver have transformed Alhambra Creek from a trickle into multiple dams and beaver ponds, which in turn, led to the return of numerous birds, steelhead trout (Oncorhynchus mykiss) and river otter (Lontra canadensis) in 2008, and mink (Neovison vison) in 2009. Examples of the impact of the beaver as a keystone species in 2010, include a green heron (Butorides virescens) catching a tule perch (Hysterocarpus traskii traskii), the first recorded sighting of the perch in Alhambra Creek and the December arrival of a pair of hooded mergansers (Lophodytes cucullatus) (see photos). The beaver parents have produced babies every year since their 2006 arrival. However, in June, 2010, after birthing and successfully weaning triplets this year (and quadruplets the previous three years), "Mom Beaver" died of natural causes.
In November, 2009 the Martinez City Council approved the placement of an 81 tile wildlife mural on the Escobar Street bridge.  The mural was created by schoolchildren and donated by Worth a Dam to memorialize the beavers and other fauna in Alhambra Creek.
The Martinez beavers probably originated from the Sacramento-San Joaquin River Delta. Historically, before the California Fur Rush of the late 18th and early 19th centuries, the Delta probably held the largest concentration of beaver in North America. It was California's early fur trade, more than any other single factor, that opened up the West, and the San Francisco Bay Area in particular, to world trade. The Spanish, French, English, Russians and Americans engaged in the California fur trade before 1825, harvesting prodigious quantities of beaver, river otter, marten, fisher, mink, fox, weasel, harbor and fur seals and sea otter. When the coastal and oceanic fur industry began to decline, the focus shifted to California's inland fur resources. Between 1826 and 1845 the Hudson's Bay Company sent parties out annually from Fort Astoria and Fort Vancouver into the Sacramento and the San Joaquin valleys as far south as French Camp on the San Joaquin River. These trapping expeditions must have been extremely profitable to justify the long overland trip each year. It appears that the golden beaver (castor canadensis, subspecies: subauratus) was one of the most valued of the animals taken, and apparently was found in great abundance. Thomas McKay reported that in one year the Hudson's Bay Company took 4,000 beaver skins on the shores of San Francisco Bay. At the time, these pelts sold for US$2.50 a pound or about US$4.00 each. The Delta area incidentally, is probably where McKay was so successful, rather than the Bay itself. In 1840, explorer Captain Thomas Farnham wrote that beaver were very numerous near the mouths of the Sacramento and San Joaquin rivers and on the hundreds of small "rushcovered" islands. Farnham, who had travelled extensively in North America, said: "There is probably no spot of equal extent in the whole continent of America which contains so many of these muchsought animals."
Alhambra Creek