Bay Nature magazineJuly-September 2008

The Bay

Warm Springs Unit Expansion

July 1, 2008

With no April showers, the largest vernal pool in the Warm Springs Unit of the Don Edwards San Francisco Bay National Wildlife Refuge in Fremont was nothing more than a small mud puddle by the first week of May. Curly dock and European grasses surrounded the dried and cracked mud rendered white and furry from dried algal mats. Swaths of purple downingia and a few dried-up Contra Costa goldfields carpeted the dried-up portions of the pool, and the recently dried mud ring around the last puddle of water was stamped with the three-pronged footprints of shorebirds.

“The pools dried out before the California tiger salamander larvae finished growing. Most of them never even got their legs,” says Meg Marriott, a biologist with the U.S. Fish and Wildlife Service. “The shorebirds had a feast.”

Drought years are nothing new to the flora and fauna endemic to vernal pools; California tiger salamanders, vernal pool tadpole shrimp, and Contra Costa goldfields have adapted to annual fluctuations in rainfall. The storm that the species can’t weather, however, is a complete loss of habitat. Throughout California, 90 percent of vernal pools have been filled or developed, so an actively protected and managed refuge such as the 275-acre Warm Springs Unit is vital to the threatened and endangered species that depend on vernal pools.

Earlier this year, 440 acres of uplands, vernal pools, and wetlands were added to the Warm Springs refuge. Two parcels contiguous with the Warm Springs Unit together make up the Pacific Commons Preserve, a mitigation project carried out by Catellus Development Group. On vernal pool land that was once grazed, farmed, and later capped by a racetrack and an airport, Catellus and environmental consultants WRA created new vernal pools and wetland meadows on 97 acres, while leaving 59 acres of existing pool and meadow habitat intact. The preserve was given to the Don Edwards San Francisco Bay National Wildlife Refuge by Catellus as mitigation for the development of a nearby commercial site, Pacific Commons. The Oakland Athletics have proposed building a new ballpark on one undeveloped part of Pacific Commons. To receive notices on public meetings about the ballpark proposal, email

About the Author

Writer Aleta George trained as a Jepson Prairie docent in 2009. In addition to writing Bay Nature's Ear to the Ground column, she has written for Smithsonian, High Country News, and the Los Angeles Times.

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