Don Edwards SF Bay National Wildlife Refuge Exploration

This is how this part of Alviso Slough looks today, but it's also a glimpse back in time. Hundreds of years ago, much of the wetlands surrounding the bay may have looked like this. Salt marshes, like this one, are rich habitats that provide shelter and food for many species, some endangered or threatened.

An aerial panorama looking north from the Marina Park trailhead, from the ruins of the Bayside Canning Company (left) near the ribbon-like Alviso Slough, to the Southern Pacific railroad tracks on the right. The reeds now fill in what was once a boat marina.

Image source: Cris Benton

The endangered California Clapper Rail once inhabited coastal marshes throughout central and northern California, but now are found only around the bay. Clapper rails like to hide in tall, dense high-marsh vegetation. Maybe you'll hear the harsh call that gives the bird its name: kek-kek-kek-kek-kek!

Image source: Wikipedia

This is a remnant of waterway from before the levees were breached to restore the wetlands. Until the mid-19th century, tidal waves washed over the mud flats at the marshy edges of the bay. The bay water that ebbed and flowed here supported a web of life ranging from microorganisms to mammals.


From above, these ghostly vestigial channels have been frozen in place since the wetlands were diked. Their shapes are memories of the tidal ebb and flow, evident in the water they retain or the salt left behind when they dry out for the season.

Image source: Cris Benton

To the right of the trail and elsewhere on this hike you'll see collections of upright sticks. Someone has painted faces on a few of them. What purpose did the sticks once serve? Who put them here? Maybe you have some ideas!

Here's an overhead view of another collection of sticks. The sticks seem to be associated with former marsh channels.

Image source: Cris Benton

"Pyramid Rock" is one of the sampling sites that produced many of the microscopic images and samples seen in this Exploration.

From above, you can see a series of small, lateral streamlets running from the railroad embankment just beyond the top of the picture frame.
Image source: Cris Benton

Codium is a genus of Siphonous Alga, although it looks like moss when it is growing in large clumps. The velvet is deceptive, it is actually composed of many long cellular "tubes" growing together.

Image source: Wayne Lanier

See the dark lines in the mud? They could be strands of vegetation. But look closer...

Image source: Cris Benton

Perhaps they're veins in a rock...

They're the tracks left by sandpipers as they look for food in the mud. Look for other clues to the animals that live and feed here. Perhaps you'll see the paw prints of a fox, or some bones or feathers, or some raccoon scat. All of this evidence tells you who's been visiting the wetlands.

Image source: Chuq Von Rospach

This is referred to informally as the 'Alviso Weep.' It the time of this photo, it was awash with reds, purples, oranges, yellows and blacks.

An aerial view of the same pond in August shows a very different scene. There is more water and the reddish color of December is here replaced mostly with green. An algal bloom along the pond's edge is just past prime. See the bird tracks?

Image source: Cris Benton

This photomicrograph shows two common salt marsh pond mat organisms: The communal diatom Melosirs (brown) ; and, Cyanobacteria (green).

Image source: Wayne Lanier

A casual observer might think rust or chemicals give the water its red, purple, yellow, and black colors. Actually, the colors come from the microorganisms that live in the water. They change by the season, month, and even week, depending on the salinity of the water and other conditions.

Biologist Wayne Lanier samples the water to see what's living here.

This large red diatom lives in the orange-red mud. Earlier in the year it dominated the surrounding waters, but by the fall it was reduced to a small orange-red mud area.

Image source: Wayne Lanier

Salt pond A15, across the trail from the Alviso Weep collecting site, taken from close to the surface of the water.

Image source: Cris Benton

Same salt pond, same day, but the photo was taken from 30 feet up. The salinity level is 16 percent.

Image source: Cris Benton

A chubby diatom and filament of Cyanobacteria among the Cylindrothecia diatoms, from the yellow mud of the main Weep stream, near Drawbridge, in the Don Edwards San Francisco Bay Wildlife Reserve. Magnification 400x.

Image source: Wayne Lanier

If you look out over the marsh you might be able to make out some pieces of wood nearly overgrown by vegetation. That's all that's left of the town of Drawbridge, on Station Island, once a settlement of about 100 homes, hotels, gun clubs, brothels, and bars.

From above it's easier to see the dozen or so buildings of the ghost town of Drawbridge. Created in 1876, the town was the home of the operator of the Southern Pacific Railroad drawbridges.

Image source: Cris Benton

You aren't likely to catch a glimpse of one current resident of Drawbridge: the endangered salt marsh harvest mouse (Reithrodontomys raviventris). This rodent lives in dense pickleweed of the middle and high zones of tidal salt marshes.

Image Source: EPA Paul Kelly